People get (inherit) their chromosomes, which contain their genes, from their parents. Chromosomes come in pairs and humans have 46 chromosomes, in 23 pairs. Children randomly get one of each pair of chromosomes from their mother and one of each pair from their father. The chromosomes that form the 23rd pair are called the sex chromosomes. They decide if a person is born a male or female. A female has two X chromosomes, and a male has one X and one Y chromosome. Each daughter gets an X from her mother and an X from her father. Each son gets an X from his mother and a Y from his father.

Genetic disorders can happen for many reasons. Genetic disorders often are described in terms of the chromosome that contains the gene that is changed in people who have the disorder. If the gene is on one of the first 22 pairs of chromosomes, called the autosomes, the genetic disorder is called an autosomal condition. If the gene is on the X chromosome, the disorder is called X-linked.

Genetic disorders also are grouped by how they run in families. Disorders can be dominant or recessive, depending on how they cause conditions and how they run in families.

Dominant

Dominant diseases can be caused by only one copy of a gene having a DNA mutation. If one parent has the disease, each child has a 50% chance of inheriting the mutated gene.

Recessive

For recessive diseases, both copies of a gene must have a DNA mutation in order to get one of these diseases. If both parents have one copy of the mutated gene, each child has a 25% chance of having the disease, even though neither parent has it. In such cases, each parent is called a carrier of the disease. They can pass the disease on to their children, but do not have the disease themselves.

Single Gene Disorders

Some genetic diseases are caused by a DNA mutation in one of a person’s genes. For example, suppose part of a gene usually has the sequence TAC. A mutation can change the sequence to TTC in some people. This change in sequence can change the way that the gene works, for example by changing the protein that is made. Mutations can be passed down to a child from his or her parents. Or, they can happen for the first time in the sperm or egg, so that the child will have the mutation but the parents will not. Single gene disorders can be autosomal or X-linked.

For example, sickle cell disease is an autosomal single gene disorder. It is caused by a mutation in a gene found on chromosome 11. Sickle cell disease causes anemia and other complications. Fragile X syndrome, on the other hand, is an X-linked single gene disorder. It is caused by a change in a gene on the X chromosome. It is the most common known cause of intellectual disability and developmental disability that can be inherited (passed from one generation to the next).

Different Number of Chromosomes

People usually have 23 pairs of chromosomes. But, sometimes a person is born with a different number. Having an extra chromosome is called trisomy. Missing a chromosome is called monosomy.

For example, people with Down syndrome have an extra copy of chromosome 21. This extra copy changes the body’s and brain’s normal development and causes intellectual and physical problems for the person. Some disorders are caused by having a different number of sex chromosomes. For example, people with Turner syndrome usually have only one sex chromosome, an X. Women with Turner syndrome can have problems with growth and heart defects.

Changes in Chromosomes

Sometimes chromosomes are incomplete or shaped differently than usual. Missing a small part of a chromosome is called a deletion. A translocation is when part of one chromosome has moved to another chromosome. An inversion is when part of a chromosome has been flipped over.

For example, people with Williams syndrome are missing a small part of chromosome 7. This deletion can result in intellectual disability and a distinctive facial appearance and personality.

Complex Conditions

A complex disease is caused by both genetic changes and environmental factors. Complex diseases also are called multifactorial. Most chronic diseases, such as heart disease, cancer, and diabetes, are complex conditions. For example, while some cases of cancer are associated with inherited genetic changes, for example, Lynch syndrome and hereditary breast and ovarian cancer, the majority most likely are caused by changes in several genes acting together with environmental exposures.

What are genes?

Genes are segments of DNA that contain instructions for building the molecules that make the body work. Most of the molecules are proteins. Parents pass their genes to their offspring.

What is a genome?

A genome is all of the genetic material in an organism. It is made of DNA (or RNA in some viruses) and includes genes and other elements that control the activity of those genes.

Does everybody have the same genome?

The human genome is mostly the same in all people. But there are variations across the genome. This genetic variation accounts for about 0.001 percent of each person's DNA and contributes to differences in appearance and health. People who are closely related have more similar DNA.

Some of the variations between individuals result from epigenetic changes. These changes arise from chemical tags that attach to DNA and affect how cells read DNA’s instructions. Epigenetic changes can be inherited.

Is genetic variation related to health and disease?

Many differences in DNA have no effect on health or disease risk. But some do. Because parents pass their genes on to their offspring, some diseases tend to cluster in families, similar to other inherited traits.

Genetic variations can influence how people respond to certain medicines, as well.

What does it mean to have a genetic risk?

Having a genetic risk means that a person has inherited the tendency to develop a certain illness. It does not mean that he or she will definitely develop the illness. Rather, it means there is a higher chance of developing it than if he or she did not have the risk.

What can a genetic test reveal?

A genetic test can identify genetic variations that studies have linked to the risk of developing a specific disease or of passing a disease gene on to descendants. A genetic test can also indicate how a person might respond to certain medicines.

Why does genetic research sometimes involve specific population groups?

Population groups often include people with the same ancestry and therefore very similar genomes. Plus, populations may share diets, environments and other characteristics that influence health. These genetic and environmental similarities make it easier for scientists to spot rare differences in a population group that could be related to health or disease. Such studies also can help explain why some medical conditions are more common in certain population groups.

Can researchers study someone's genes without permission?

Scientists who conduct research with people follow strict rules. Among other things, they must obtain signed consent from participants. And before collecting blood, cheek swabs or other samples that contain DNA, researchers must tell participants the purpose of the study, how they will use the samples, and whether and for how long they will store the samples.

Why do scientists study the genes of other organisms?

All living things evolved from a common ancestor. Therefore, humans, animals and other organisms share many of the same genes, and the molecules made from them function in similar ways. For example, the human and mouse genomes are about 85 percent the same. Two-thirds of human genes known to be involved in cancer have counterparts in the fruit fly.

Researchers have found many genes that have been preserved in multiple organisms for millions of years. They can study these preserved genes and compare the genomes of different species to find similarities and differences that improve their understanding of how human genes function and are controlled. This helps researchers develop new strategies to treat and prevent human disease. Scientists also study the genes of bacteria, viruses and fungi to find ways to prevent or treat infection. Increasingly, these studies are helping them understand how microbes on and in the body affect human health, sometimes in beneficial ways.

Psychological researchers study genetics in order to better understand the biological basis that contributes to certain behaviors. While all humans share certain biological mechanisms, we are each unique. And while our bodies have many of the same parts—brains and hormones and cells with genetic codes—these are expressed in a wide variety of behaviors, thoughts, and reactions.

Why do two people infected by the same disease have different outcomes: one surviving and one succumbing to the ailment? How are genetic diseases passed through family lines? Are there genetic components to psychological disorders, such as depression or schizophrenia? To what extent might there be a psychological basis to health conditions such as childhood obesity?

To explore these questions, let’s start by focusing on a specific disease, sickle-cell anemia, and how it might affect two infected sisters. Sickle-cell anemia is a genetic condition in which red blood cells, which are normally round, take on a crescent-like shape (Figure). The changed shape of these cells affects how they function: sickle-shaped cells can clog blood vessels and block blood flow, leading to high fever, severe pain, swelling, and tissue damage.

Many people with sickle-cell anemia—and the particular genetic mutation that causes it—die at an early age. While the notion of “survival of the fittest” may suggest that people suffering from this disease have a low survival rate and therefore the disease will become less common, this is not the case. Despite the negative evolutionary effects associated with this genetic mutation, the sickle-cell gene remains relatively common among people of African descent. Why is this? The explanation is illustrated with the following scenario.

Imagine two young women—Luwi and Sena—sisters in rural Zambia, Africa. Luwi carries the gene for sickle-cell anemia; Sena does not carry the gene. Sickle-cell carriers have one copy of the sickle-cell gene but do not have full-blown sickle-cell anemia. They experience symptoms only if they are severely dehydrated or are deprived of oxygen (as in mountain climbing). Carriers are thought to be immune from malaria (an often deadly disease that is widespread in tropical climates) because changes in their blood chemistry and immune functioning prevent the malaria parasite from having its effects (Gong, Parikh, Rosenthal, & Greenhouse, 2013). However, full-blown sickle-cell anemia, with two copies of the sickle-cell gene, does not provide immunity to malaria.

While walking home from school, both sisters are bitten by mosquitos carrying the malaria parasite. Luwi does not get malaria because she carries the sickle-cell mutation. Sena, on the other hand, develops malaria and dies just two weeks later. Luwi survives and eventually has children, to whom she may pass on the sickle-cell mutation.

Malaria is rare in the United States, so the sickle-cell gene benefits nobody: the gene manifests primarily in health problems—minor in carriers, severe in the full-blown disease—with no health benefits for carriers. However, the situation is quite different in other parts of the world. In parts of Africa where malaria is prevalent, having the sickle-cell mutation does provide health benefits for carriers (protection from malaria).

This is precisely the situation that Charles Darwin describes in the theory of evolution by natural selection (Figure). In simple terms, the theory states that organisms that are better suited for their environment will survive and reproduce, while those that are poorly suited for their environment will die off. In our example, we can see that as a carrier, Luwi’s mutation is highly adaptive in her African homeland; however, if she resided in the United States (where malaria is much less common), her mutation could prove costly—with a high probability of the disease in her descendants and minor health problems of her own.

Genetic Variation

Genetic variation, the genetic difference between individuals, is what contributes to a species’ adaptation to its environment. In humans, genetic variation begins with an egg, about 100 million sperm, and fertilization. Fertile women ovulate roughly once per month, releasing an egg from follicles in the ovary. During the egg's journey from the ovary through the fallopian tubes, to the uterus, a sperm may fertilize an egg.

The egg and the sperm each contain 23 chromosomes. Chromosomes are long strings of genetic material known as deoxyribonucleic acid (DNA). DNA is a helix-shaped molecule made up of nucleotide base pairs. In each chromosome, sequences of DNA make up genes that control or partially control a number of visible characteristics, known as traits, such as eye color, hair color, and so on. A single gene may have multiple possible variations, or alleles. An allele is a specific version of a gene. So, a given gene may code for the trait of hair color, and the different alleles of that gene affect which hair color an individual has.

When a sperm and egg fuse, their 23 chromosomes pair up and create a zygote with 23 pairs of chromosomes. Therefore, each parent contributes half the genetic information carried by the offspring; the resulting physical characteristics of the offspring (called the phenotype) are determined by the interaction of genetic material supplied by the parents (called the genotype). A person’s genotype is the genetic makeup of that individual. Phenotype, on the other hand, refers to the individual’s inherited physical characteristics, which are a combination of genetic and environmental influences (Figure).

Most traits are controlled by multiple genes, but some traits are controlled by one gene. A characteristic like cleft chin, for example, is influenced by a single gene from each parent. In this example, we will call the gene for cleft chin “B,” and the gene for smooth chin “b.” Cleft chin is a dominant trait, which means that having the dominant allele either from one parent (Bb) or both parents (BB) will always result in the phenotype associated with the dominant allele. When someone has two copies of the same allele, they are said to be homozygous for that allele. When someone has a combination of alleles for a given gene, they are said to be heterozygous. For example, smooth chin is a recessive trait, which means that an individual will only display the smooth chin phenotype if they are homozygous for that recessive allele (bb).

Imagine that a woman with a cleft chin mates with a man with a smooth chin. What type of chin will their child have? The answer to that depends on which alleles each parent carries. If the woman is homozygous for cleft chin (BB), her offspring will always have cleft chin. It gets a little more complicated, however, if the mother is heterozygous for this gene (Bb). Since the father has a smooth chin—therefore homozygous for the recessive allele (bb)—we can expect the offspring to have a 50% chance of having a cleft chin and a 50% chance of having a smooth chin (Figure).

Sickle-cell anemia is just one of many genetic disorders caused by the pairing of two recessive genes. For example, phenylketonuria (PKU) is a condition in which individuals lack an enzyme that normally converts harmful amino acids into harmless byproducts. If someone with this condition goes untreated, he or she will experience significant deficits in cognitive function, seizures, and increased risk of various psychiatric disorders. Because PKU is a recessive trait, each parent must have at least one copy of the recessive allele in order to produce a child with the condition (Figure).

So far, we have discussed traits that involve just one gene, but few human characteristics are controlled by a single gene. Most traits are polygenic: controlled by more than one gene. Height is one example of a polygenic trait, as are skin color and weight.

Where do harmful genes that contribute to diseases like PKU come from? Gene mutations provide one source of harmful genes. A mutation is a sudden, permanent change in a gene. While many mutations can be harmful or lethal, once in a while, a mutation benefits an individual by giving that person an advantage over those who do not have the mutation. Recall that the theory of evolution asserts that individuals best adapted to their particular environments are more likely to reproduce and pass on their genes to future generations. In order for this process to occur, there must be competition—more technically, there must be variability in genes (and resultant traits) that allow for variation in adaptability to the environment. If a population consisted of identical individuals, then any dramatic changes in the environment would affect everyone in the same way, and there would be no variation in selection. In contrast, diversity in genes and associated traits allows some individuals to perform slightly better than others when faced with environmental change. This creates a distinct advantage for individuals best suited for their environments in terms of successful reproduction and genetic transmission.

Gene-Environment Interactions

Genes do not exist in a vacuum. Although we are all biological organisms, we also exist in an environment that is incredibly important in determining not only when and how our genes express themselves, but also in what combination. Each of us represents a unique interaction between our genetic makeup and our environment; range of reaction is one way to describe this interaction. Range of reaction asserts that our genes set the boundaries within which we can operate, and our environment interacts with the genes to determine where in that range we will fall. For example, if an individual’s genetic makeup predisposes her to high levels of intellectual potential and she is reared in a rich, stimulating environment, then she will be more likely to achieve her full potential than if she were raised under conditions of significant deprivation. According to the concept of range of reaction, genes set definite limits on potential, and environment determines how much of that potential is achieved. Some disagree with this theory and argue that genes do not set a limit on a person’s potential.

Another perspective on the interaction between genes and the environment is the concept of genetic environmental correlation. Stated simply, our genes influence our environment, and our environment influences the expression of our genes (Figure). Not only do our genes and environment interact, as in range of reaction, but they also influence one another bidirectionally. For example, the child of an NBA player would probably be exposed to basketball from an early age. Such exposure might allow the child to realize his or her full genetic, athletic potential. Thus, the parents’ genes, which the child shares, influence the child’s environment, and that environment, in turn, is well suited to support the child’s genetic potential.

In another approach to gene-environment interactions, the field of epigenetics looks beyond the genotype itself and studies how the same genotype can be expressed in different ways. In other words, researchers study how the same genotype can lead to very different phenotypes. As mentioned earlier, gene expression is often influenced by environmental context in ways that are not entirely obvious. For instance, identical twins share the same genetic information (identical twins develop from a single fertilized egg that split, so the genetic material is exactly the same in each; in contrast, fraternal twins develop from two different eggs fertilized by different sperm, so the genetic material varies as with non-twin siblings). But even with identical genes, there remains an incredible amount of variability in how gene expression can unfold over the course of each twin’s life. Sometimes, one twin will develop a disease and the other will not. In one example, Tiffany, an identical twin, died from cancer at age 7, but her twin, now 19 years old, has never had cancer. Although these individuals share an identical genotype, their phenotypes differ as a result of how that genetic information is expressed over time. The epigenetic perspective is very different from range of reaction, because here the genotype is not fixed and limited.

Genes affect more than our physical characteristics. Indeed, scientists have found genetic linkages to a number of behavioral characteristics, ranging from basic personality traits to sexual orientation to spirituality (for examples, see Mustanski et al., 2005; Comings, Gonzales, Saucier, Johnson, & MacMurray, 2000). Genes are also associated with temperament and a number of psychological disorders, such as depression and schizophrenia. So while it is true that genes provide the biological blueprints for our cells, tissues, organs, and body, they also have significant impact on our experiences and our behaviors.

Let’s look at the following findings regarding schizophrenia in light of our three views of gene-environment interactions. Which view do you think best explains this evidence?

In a study of people who were given up for adoption, adoptees whose biological mothers had schizophrenia and who had been raised in a disturbed family environment were much more likely to develop schizophrenia or another psychotic disorder than were any of the other groups in the study:

• Of adoptees whose biological mothers had schizophrenia (high genetic risk) and who were raised in disturbed family environments, 36.8% were likely to develop schizophrenia.
• Of adoptees whose biological mothers had schizophrenia (high genetic risk) and who were raised in healthy family environments, 5.8% were likely to develop schizophrenia.
• Of adoptees with a low genetic risk (whose mothers did not have schizophrenia) and who were raised in disturbed family environments, 5.3% were likely to develop schizophrenia.
• Of adoptees with a low genetic risk (whose mothers did not have schizophrenia) and who were raised in healthy family environments, 4.8% were likely to develop schizophrenia (Tienari et al., 2004).

The study shows that adoptees with high genetic risk were especially likely to develop schizophrenia only if they were raised in disturbed home environments. This research lends credibility to the notion that both genetic vulnerability and environmental stress are necessary for schizophrenia to develop, and that genes alone do not tell the full tale.

Summary

Genes are sequences of DNA that code for a particular trait. Different versions of a gene are called alleles—sometimes alleles can be classified as dominant or recessive. A dominant allele always results in the dominant phenotype. In order to exhibit a recessive phenotype, an individual must be homozygous for the recessive allele. Genes affect both physical and psychological characteristics. Ultimately, how and when a gene is expressed, and what the outcome will be—in terms of both physical and psychological characteristics—is a function of the interaction between our genes and our environments.

What is a cell?

Cells are the basic building blocks of all living things. The human body is composed of trillions of cells. They provide structure for the body, take in nutrients from food, convert those nutrients into energy, and carry out specialized functions. Cells also contain the body’s hereditary material and can make copies of themselves.

Cells have many parts, each with a different function. Some of these parts, called organelles, are specialized structures that perform certain tasks within the cell. Human cells contain the following major parts, listed in alphabetical order:

Cytoplasm

Within cells, the cytoplasm is made up of a jelly-like fluid (called the cytosol) and other structures that surround the nucleus.

Cytoskeleton

The cytoskeleton is a network of long fibers that make up the cell’s structural framework. The cytoskeleton has several critical functions, including determining cell shape, participating in cell division, and allowing cells to move. It also provides a track-like system that directs the movement of organelles and other substances within cells.

Endoplasmic reticulum (ER)

This organelle helps process molecules created by the cell. The endoplasmic reticulum also transports these molecules to their specific destinations either inside or outside the cell.

Golgi apparatus

The Golgi apparatus packages molecules processed by the endoplasmic reticulum to be transported out of the cell.

Lysosomes and peroxisomes

These organelles are the recycling center of the cell. They digest foreign bacteria that invade the cell, rid the cell of toxic substances, and recycle worn-out cell components.

Mitochondria

Mitochondria are complex organelles that convert energy from food into a form that the cell can use. They have their own genetic material, separate from the DNA in the nucleus, and can make copies of themselves.

Nucleus

The nucleus serves as the cell’s command center, sending directions to the cell to grow, mature, divide, or die. It also houses DNA (deoxyribonucleic acid), the cell’s hereditary material. The nucleus is surrounded by a membrane called the nuclear envelope, which protects the DNA and separates the nucleus from the rest of the cell.

Plasma membrane

The plasma membrane is the outer lining of the cell. It separates the cell from its environment and allows materials to enter and leave the cell.

Ribosomes

Ribosomes are organelles that process the cell’s genetic instructions to create proteins. These organelles can float freely in the cytoplasm or be connected to the endoplasmic reticulum (see above).

Genetic research is creating new ways for people to take action and prevent disease and new ways to treat disease through personalized medicine.

Why is my family health history important?

We have known for a long time that common diseases like heart disease, asthma, cancer, and diabetes can run in families. Rare diseases like hemophilia, cystic fibrosis, and sickle cell anemia also run in families. For example, if a parent has high blood pressure, his or her child is more likely to have high blood pressure as an adult.

Learning about the health history of your family and sharing this information with your health care provider can help you learn whether you have an increased chance of getting some common diseases.

Your health care provider can then give you individualized and specific education about how to:

• Check regularly for the disease.

• Follow a healthy diet.

• Get regular exercise.

• Avoid smoking tobacco and too much alcohol.

• Get specific genetic testing that can help with diagnosis and treatment.

How do I find a genetic professional?

To help people use family history to improve their health, the U.S. Surgeon General started a national public health campaign called the U.S. Surgeon General's Family History Initiative. This goal of this campaign is to have all American families learn more about their family health history.

My Family Health Portrait is a tool from the U.S. Surgeon General's Family History Initiative that you can find on the Web. The tool helps you gather and organize your own family health history. You can find it in either English or Spanish. Using any computer with an Internet connection, you can build a drawing of your family tree and make a chart of your family health history. Both the chart and the drawing can be printed and shared with your family members or your health care provider.

Can knowing about genetics help treat disease?

Every year, more than two million Americans have serious side effects from prescription medicines and as many as one hundred thousand die. A "one-size-fits-all" approach to medicine might lead to some of these side effects, since all people are different. Genetic research is helping us figure out how individual people will respond to medicines. This type of research is called "pharmacogenetics" and "pharmagenomics."

How is genetic information used to treat disease?

A person's genetic makeup affects how their body breaks down certain medicines. Genetic testing can examine certain liver enzymes in a person to find out how their body breaks down and removes medicines from the body. Because these liver enzymes are less active in some people, they are less able to break down and get rid of some medicines. This can lead to serious side effects. This type of testing is being used to find the right dose of certain medicines, such as antidepressants that are used to treat some mental illnesses.

• There is now a test to find out whether a medicine called Herceptin will be an effective treatment in breast cancer. This test looks "estrogen receptors" in tumors.

• Children with a common type of childhood leukemia can be tested to find the right doses of chemotherapy treatment.

What are some concerns?

Some people have concerns about using genetic information in the treatment of disease. These concerns include:

• Tailor-made medicines might be more expensive

• Not everyone might have access to new treatments

• Keeping genetic information private

• Possible discrimination at work and from health insurance companies

• Need for more information about this type of medicine

A

Active site

The region on an enzyme's surface where only a specific substrate can bind, resulting in a che mical reaction.

ADME

An acronym describing pharmacokinetic processes that pharmacologists study regarding drugs in the body: absorption, distribution, metabolism (break down), and excretion . Sometimes, toxicity is included in this list through the acronyms ADMET or ADME-Tox.

Agonist

(AG-uh-nist) A molecule that binds to a receptor in a cell to trigger a response, such as muscle contraction or hormone release.

Amino acid

(uh-MEE-no) A chemical building block of proteins. There are 20 standard amino acids, each of which has the same basic structure with a different side chain. The side chain gives the amino acid its unique properties.

Analgesic

(an-l-JEE-zik) An agent or drug that reduces pain without affecting consciousness.

Anesthesia

(an-uhs-THEE-zhuh) Anesthesia is a medical treatment that prevents patients from feeling pain during procedures like surgery, certain screening and diagnostic tests, tissue sample removal (e.g., skin biopsies), and dental work.

Anesthesiologist

Anesthesiologists are doctors specializing in the field of anesthesiology. They administer anesthetics and carefully monitor patients throughout surgery and during recovery.

Anesthesiology

(an-uhs-thee-zee-OL-uh-jee) The medical field related to using anesthetic drugs to prevent patients from feeling pain during surgery. Doctors in this field, called anesthesiologists, carefully monitor patients throughout surgery and during recovery.

Anesthetic

An anesthetic is a medicine used to prevent pain during procedures like surgery and dental work.

Aneuploidy

When a cell has the wrong number of chromosomes, either more or less than it should.

Antagonist

(an-TAG-uh-nist) A molecule that binds to a receptor in a cell to prevent a response, such as a muscle contraction or hormone release. For example, some medicines to treat opioid addiction bind to opioid receptors, blocking heroin or other opioids from activating them.

Antibiotic

A medicine that can kill bacteria or keep them from growing.

Antibiotic resistance

When bacteria change in ways that make antibiotic medicines ineffective.

Antibody

A protein the immune system produces in response to a foreign substance such as a virus or bacterium.

Antigen

T he parts of an infectious organism that the immune system recognizes are foreign to the human body.

Anti-inflammatory

A drug that reduces inflammation.

Antimicrobial

A substance that kills microorganisms such as bacteria or mold, or stops them from growing and causing disease.

Antioxidant

(an-tee-OCK-si-duhnt) A natural or human-made substance that may prevent or delay some types of cell damage. The body and many foods, including fruits and vegetables, naturally produce antioxidants.

Apoptosis

(ap-uhp-TOH-sis) A process in which cells in the body die in a controlled and predictable way because they have DNA damage or are not needed. One other type of cell death is necrosis.

Artificial intelligence

A feature where machines learn to perform tasks, rather than simply carrying out computations that are input by human users. Early applications of AI included machines that could play games such as checkers and chess, and programs that could reproduce language.

Atom

A fundamental unit of matter, the substance a physical object is composed of, consisting of a nucleus and electrons.

ATP, adenosine triphosphate

(ah-DEH-no-seen try-FOSS-fate)The major source of energy for biochemical reactions in all organisms. ATP is formed when animals digest food or plants undergo photosynthesis. Energy is released when certain chemical bonds in ATP are broken.

Autophagy

(aw-TAH-fuh-jee) A natural breakdown-recycle process within a cell. The cell breaks down and destroys old, damaged, or abnormal proteins and other substances within its cytoplasm, including bacteria and viruses. It then recycles them for important cellular functions.

B

Bacterium

(bak-TEER-ee-uhm) (plural: bacteria) A one-celled microorganism without a nucleus. Bacteria live almost everywhere in the environment. Some bacteria may infect humans, plants, or animals. They may be harmless, or they may cause disease. Scientists often use bacteria as research organisms to stu dy basic biological processes.

Bioavailability

How quickly and to what extent the active part of a drug is absorbed by the body and is available at the site where it’s needed.

Biochemistry

The scientific study of the chemistry of living cells, tissues, organs, and organisms.

Biodegradable

Capable of being broken down physically and/or chemically by microorganisms.

Biofilm

A highly organized community of microorganisms that develops naturally on certain surfaces. Biofilms can be helpful in treatment of wastewater, for example. But they can also be harmful, like when they form on medical devices implanted in people. These biofilms are highly resistant to antibiotic medicines.

Bioinformatics

A field of research that relies on computers to store and analyze large amounts of biological data.

Biological clock

An organism’s innate timing device. Composed of proteins that interact in cells throughout the body, these clocks produce circadian rhythms and regulate their timing.

Biomaterial

A natural or synthetic material introduced into living tissue, often as part of a medical device such as an artificial joint.

Biomedical engineering

The application of fundamental theories and analytical practices to the fields of medicine and biology. Examples include the design and production of artificial limbs and medical implants. Also called bioengineering.

Biophysics

The science of applying the theories and methods of physics to understand how biological systems work.

Biosensor

A system or device that converts a biological response into an electrical signal. For example, in a blood glucose monitor, a test strip contains an enzyme that reacts to glucose in the blood, creating an electrical signal that indicates the amount of glucose in the blood. People use biosensors in many fields, including food processing, medicine, and defense.

Biotechnology

The use of living organisms or biological systems to make useful products and processes.

Blastema

(bla-STEE-muh) A specialized bud of cells that rapidly divide to form skin, scales, mus cle, bone, or cartilage needed to create a lost limb, fin, or tail in animals such as lobsters, catfish, and lizards.

Burn

burns include:

• First degree: Damage only to the outer layer of skin (epidermis)
• Second degree: Damage to the outer layer and the layer beneath it (dermis)
• Third degree: Damage or complete destruction of both layers of skin
• Fourth degree: Extends into fat
• Fifth degree: Extends into muscle
• Sixth degree: Extends to bone

C

Carbohydrate

A chemical compound made up of only carbon, hydrogen, and oxygen, usually in the ratio 1:2:1. Carbohydrates include simple sugars like glucose and short and long chains, or polymers, of sugars bound together.

Carcinogen

(kahr-SIN-uh-jen) Any substance that causes cancer.

Catalyst

(KAT-uh-list) A substance that speeds up a chemical reaction that would have occurred without help, but at a much slower rate. Enzymes are biological catalysts.

Cell

The basic subunit of any living organism; the simplest form of life. Cells house the biological machinery that makes the proteins, chemicals, and signals responsible for everything that happens inside the body.

Cell Culture

The growth of microorganisms, such as bacteria or yeast, or animal or plant cells in the laboratory under controlled, artificial environments. Cell cultures are useful tools that scientists use for biomedical research or to diagnose infections.

Cell cycle

The steps of a cell copying its contents and dividing in two.

1. Prophase (PRO-faze): Chromosomes condense and become visible and the spindle forms. The spindle is a football-shaped array of fibers made of microtubules and associated proteins. Some of the fibers attach to the chromosomes and help draw them to opposite ends of the cell.
2. Prometaphase (pro-MET-uh-faze): The nuclear membrane breaks apart, and the spindle starts to interact with chromosomes.
3. Metaphase (MET-uh-faze): Copied chromosomes align in the middle of the spindle.
4. Anaphase (ANN-uh-faze): Chromosomes separate into two genetically identical groups and move to opposite ends of the spindle.
5. Telophase (TEE-lo-faze): Nuclear membranes form around each of the two sets of chromosomes, the chromosomes begin to spread out, and the spindle begins to break down.
6. Cytokinesis (SY-toh-kin-EE-sis): The cell splits into two daughter cells.

Interphase (IN-tur-faze) is the period in a cell's life cycle when it is not undergoing cell division. There are several checkpoints where the cycle can pause if there’s a problem, such as incomplete DNA synthesis or damaged DNA.

Central nervous system

The brain and spinal cord, which control all the workings of the body.

Channel protein

A hollow or pore-containing protein that spans a cell membrane and allows small molecules, such as charged particles (ions), to move from one side of the membrane to the other.

Chaperone

A protein that helps other proteins fold or move throughout the cell.

Chemical biology

A field that blends chemistry and biology and involves the application of chemical techniques and tools to the study of biological systems.

Chemical bond

A physical force holding atoms together to form a molecule.

• Covalent bonds form when electrons travel between the atoms' nuclei and are thus “shared.” Molecules can contain single, double, and triple covalent bonds.
• Peptide bonds are specific covalent bonds formed by joining two amino acids.
• Ionic bonds are forces that hold together two ions.
• Metallic bonds are forces that hold atoms together in a metallic substance where electrons continually move from one atom to another and are not associated with any specific pair of atoms.

Chemical library

A collection of chemicals that are stored along with related information, such as the chemical structure, purity, quantity, and other characteristics of the substance.

Cheminformatics

The use of computer and information technologies to study problems in chemistry.

Chemistry

A field of study concerned with the composition, properties, and reactions of substances.

Chemotaxis

(kee-moh-TAK-sis) The movement of a cell toward or away from a chemical force.

Chiral

Asymmetric so that the structure and its mirror image are not superimposable (identically matched when laid on top of one another). Organic molecules often have chiral carbons, where four different groups are attached to a single carbon atom . Molecules can have multiple chiral centers.

Cholesterol

A waxy lipid produced by animal cells that is a major component of cell membranes and a building block for some hormones. Cholesterol is also found in foods from animal sources. Good cholesterol carries cholesterol from other parts of your body back to your liver where it can be removed. Bad cholesterol can build up in the arteries, causing them to narrow or become blocked.

Chromatin

(KROH-muh-tin)The part of the nucleus that consists of DNA and proteins and forms chromosomes.

Chromosome

(KROH-muh-sohm) A cellular structure in the nucleus containing genes. Chromosomes are composed of DNA and proteins, and they split into two identical strands, called chromatids, during cell division. Humans have 23 pairs of chromosomes in every cell in their bodies. One of each pair is from the mother and the other is from the father.

Cilium

(SIL-ee-uhm) (plural: cilia) A hairlike projection from a cell surface. The rhythmic beating of cilia can move fluid or mucus over a cell or can allow single-celled organisms to move. Cilia are shorter than flagella.

Circadian

(sur-KAY-dee-uhn) Pertaining to a period of about 24 hours; applied especially to rhythmic biological repetition like the sleep-wake cycle and the release of some hormones, called circadian rhythms.

Clinical trial

A scientific study of an intervention in people. The intervention can be a medication, medical device, procedure, or change in behavior. The goal is to find out if the intervention is safe and effective.

Clinician

A healthcare professional who provides care for patients.

Clone

In genetics, the process of making many identical copies of a gene or a whole organism. The term also refers to the isolation and manipulation of a gene.

Cofactor

A helper molecule (either inorganic, such as a metal ion, or organic, such as a vitamin) an enzyme needs to work.

Combinatorial chemistry

The random assembly of various chemical units into chemical libraries of new synthetic compounds.

Comparative genomics

(juh-NOH-miks) The study of human genetics by comparisons with other organisms' genetics.

Compensatory hypertrophy

(kuhm-PEN-suh-tawr-ee hahy-PUR-truh-fee) In humans and some other animals, when part of an organ is removed or destroyed, the remaining portion grows to allow the organ to function as it did before. The liver can regrow to its original size. A kidney, pancreas, thyroid, adrenal gland, or lung can undergo the same process, but in a more limited way. This is one type of regeneration.

Computational biology

A field of science that uses computers to study complex biological processes that involve many molecular interactions.

Confocal laser scanning

(kon-FOH-kuhl LAY-zur SKAN-ing) A technique for light microscopy that uses a very narrow beam of light (made by the laser) to create images of 3D structures at the cell or tissue level. The narrow beam is forced through a pinhole to keep out-of-focus light from reaching the sample, which increases the resolution without blurriness. Mirrors move to reflect the beam and guide it across the sample (scanning). This technique can visualize structures at different depths in the sample.

CRISPR (clustered regularly interspaced short palindromic repeats)

An immune system in bacteria that recognizes and destroys invading DNA and maybe RNA. It’s been adapted into a gene-editing tool widely used in basic and applied research.

Crossing over

A process that occurs during meiosis, in which chromosome partners, one inherited from each parent, physically swap sections with one another. This creates hybrid chromosomes that are a patchwork of the original pair. Crossing over occurs in species that reproduce sexually and increases the genetic variety of offspring.

Cryo-electron microscopy (Cryo-EM)

A type of transmission electron microscopy (TEM) where scientists freeze a biological sample so quickly that water molecules don’t have time to form ice crystals. This keeps cellular materials in their normal place. Cold samples are more stable and can be imaged many times.

Crystal

Matter composed of atoms, ions, or molecules packed in a well-organized, repeating grid pattern.

Cyclosis

(sahy-KLOH-sis) Movement of nutrients and organelles within cells to carry out various cellular functions. The cytoplasm within the cell creates a directional flow that pushes around the content of the cells.

Cytoplasm

(SAHY-tuh-PLAZ-uhm) The material found between the cell membrane and the nuclear envelope. It includes the cytosol and all organelles except the nucleus.

Cytoskeleton

(SAHY-toh-SKEL-uh-tuhn) A collection of fibers that gives a cell shape and support and allows movement within the cell and, in some cases, by the entire cell. The three main types of cytoskeletal fibers are actin filaments, intermediate filaments, and microtubules.

• Actin filaments (AK-tin FIL-uh-muhnt) Fibers that contract or lengthen to give cells the flexibility to move and change shape. Together with the protein myosin, actin filaments are responsible for muscle contraction.
• Intermediate filaments Fibers that provide strength in things like nails, hair, the outer layer of skin, nerves, and certain organs.
• Microtubules (MY-kroh-TOO-byool) Strong, hollow fibers that act as a structural support for the cell. During cell division, microtubules form the spindle that directs chromosomes to the daughter cells. Microtubules also serve as tracks for transporting vesicles and give structure to flagella and cilia.

Cytosol

(SAHY-tuh-sol) The semi-fluid portion of the cytoplasm, excluding the organelles. The cytosol is a concentrated solution of proteins, salts, and other molecules.

D

Differentiation

(dif-uh-ren-shee-AY-shuhn) When an unspecialized cell becomes a specialized cell with a specific function. During development, embryonic stem cells differentiate into the many cell types that make up the human body. Adult stem cells differentiate into the type of tissue in which they are located to replace cells lost to age, disease, or injury.

Diploid

(DIP-loyd) A cell or organism that has paired chromosomes, one from each parent.

Distributed computing

Using a network of hundreds or thousands of computers to perform complex calculations that usually can’t be done on a single computer. For example, researchers have used distributed computing to study the dynamics of how proteins fold.

DNA (deoxyribonucleic acid)

(dee-AWK-see-RAHY-boh-noo-CLAY-ik) The substance of heredity. A long, usually double-stranded chain of nucleotides that carries the information needed for all cellular functions, including protein production.

DNA polymerase

(POL-uh-muh-rays) An enzyme that copies, and sometimes repairs, DNA.

DNA sequencing

(SEE-kwuhn-sing) Sometimes called gene or genome sequencing, a lab technique used to find the exact order of the bases in a DNA molecule. The DNA sequence carries information a cell needs to make proteins and RNA molecules.

Drug

A chemical or biological molecule that is not found naturally in the body. Medicines are specific types of regulated drugs. The term drug can also refer to drugs of abuse—substances that may or may not be medicines that people use to alter their mental or physical states.

Drug delivery

The process of giving a drug to a person or animal. Two main components of drug delivery are drug delivery systems and route of administration.

• Drug delivery systems: Engineered technologies for the targeted delivery and/or controlled release of drugs. Some examples include nanoparticles, liposomes, or other formulations that improve the drug’s ADME properties.
• Route of administration describes the method used to give the drug to the person or animal. Drugs can be given by mouth (oral); through the skin (topical), mucous membranes (nasal), or lungs (inhaled); or into a vein through a needle (intravenous).

E

Ecology

The study of the interrelationship of organisms and their environments, including their habitats, energy sources, nutrients, and other resources.

Edema

(ih-DEE-muh) Swelling caused by fluid in the body's tissues. It usually occurs in the feet, ankles, and legs, but it can involve the entire body.

Electrolyte

(ih-LEK-truh-lahyt) A mineral in the body that has an electric charge. Electrolytes help balance the amount of water in the body and the pH (acid/base) level; move nutrients into and wastes out of cells and make sure nerves, muscles, the heart, and the brain work the way they should. Electrolytes include sodium, calcium, potassium, chlorine, phosphate, and magnesium.

Electromagnetic radiation

(ih-LEK-troh-mag-NET-ik ray-dee-AY-shuhn) Energy produced in the form of a wave. It includes all kinds of radiation, including, in order of increasing energy: radio waves, microwaves, infrared radiation (heat), visible light, ultraviolet radiation (the part of sunlight that causes sunburn), X-rays, and gamma radiation (made by nuclear reactions).

Electron

A very small particle that has a negative charge of electricity and travels around the nucleus of an atom .

Electron microscopy

A technique that uses beams of fast-moving electrons instead of light to magnify samples. Powerful magnets focus the electrons into an image.

Element

A pure substance that can't be chemically separated into simpler substances. Carbon, hydrogen, and oxygen are fundamental elements in biology.

Endocytosis

(en-doh-sahy-TOH-sis) A process cells use to absorb nutrients, fluids, proteins, and other molecules. The cell membrane curves inward, encircling the material, then pinches off, producing a vesicle inside the cell.

Endogenous

(en-DAH-jeh-nuhs) Produced inside an organism or cell. The opposite is external (exogenous) production.

Endoplasmic reticulum (ER)

(EN-doh-plaz-mik reh-TIK-yuh-luhm) An organelle made up of interconnected tubes and flattened sacs. There are two kinds of ER: rough (because it is dotted with ribosomes) ER, which processes newly made proteins , and smooth ER, which helps make lipids and neutralize toxins.

Enzyme

(EN-zahym) A biological catalyst that is almost always a protein and speeds up the rate of a specific chemical reaction in the cell by reducing the amount of energy needed for the reaction to proceed .

Epigenetics

(ep-ih-juh-NET-iks) The study of changes in gene expression or phenotypes that are not the result of changes in DNA sequence.

Eukaryotic cell

(yoo-KAYR-ee-ah-tik) A cell with a membrane-bound nucleus and other organelles not found in prokaryotic cells. Eukaryotic cells make up animals, plants, fungi, and some single-celled organisms.

Evolution

The process by which an organism's genome changes and gives rise to a beneficial trait that allows it to be better adapted to its surroundings. The best-adapted individuals in a population will have the fittest offspring. Over many generations, members of the species with the beneficial trait may take on new roles and may evolve into a new species.

Exocytosis

(ek-soh-sahy-TOH-sis) A process cells use to dump wastes outside of the cell via vesicles.

Extracellular matrix

(ek-struh-SEL-yuh-ler MEY-triks) The material around, within, and between the body's organs, tissues, and cells. In some tissues, it's a thin layer separating cells. In others, it's the major component. The extracellular matrix is most prevalent in connective tissue, the material that forms our skeletons, cushions our internal organs, and winds between blood vessels and around nerves.

F

Flagellum

(fluh-JEL-uhm) (plural: flagella) A long, tail-like structure extending from a cell. Sperm and many microorganisms move using flagella.

Fluorescence

(floh-RES-uhns) Giving off light at one wavelength (emission) after absorbing light of a different wavelength (excitation). Researchers use fluorescent dyes to take images of cells.

Fungus

(plural: fungi) A plantlike, eukaryotic organism that does not make chlorophyll. Examples include mushrooms, yeasts , and molds. Fungi live throughout the environment and in the human body. Some types of fungi can cause disease.

G

G protein

A protein located inside the cell membrane that helps transmit signals from hormones into cells.

Gene

A unit of heredity; a segment of DNA that contains the code for making a specific protein or RNA molecule.

Gene expression

When the information in a gene directs the building of a protein. The cell reads the gene in groups of three nucleotides. Each of these groups corresponds to one of 20 different amino acids used to build the protein.

Genetic code

The instructions in a gene that tell the cell how to make a specific protein.

Genetic engineering

The manipulation of an organism's genes—introducing, eliminating, or changing them—using modern molecular biology techniques.

Genetics

The scientific study of genes and heredity—of how certain qualities or traits are passed from parents to offspring as a result of changes in DNA sequence.

Genome

(JEE-nohm) All of an organism's genetic material.

Genomics

(jee-NOHM-iks) The study of all of an organism's genetic material.

Genotype

(JEE-nuh-tahyp): An individual’s collection of genes. Genotypes are expressed when its genetic code is used to make protein and RNAmolecules. This expression contributes to the individual’s observable traits, called the pheno type .

Glycolipid

(glahy-koh-LIP-id) A lipid bound to a sugar.

Glycoprotein

(glahy-koh-PROH-teen) A protein bound to a sugar.

Glycoscience

(glahy-koh-SAHY-uhns) A branch of chemistry dedicated to the study of the many types of carbohydrate molecules.

Glycosylation

(glahy-kah-sih-LAY-shun) The process of adding specialized chains of sugar molecules to proteins or lipids; occurs in the endoplasmic reticulum and Golgi.

Golgi

(GAWL-jee) Also called the Golgi apparatus or Golgi complex; an organelle composed of membranous sacs in which many newly made proteins mature and become functional.

H

Haploid

(HAP-loid) A cell with one copy of each chromosome, as in a sperm or egg.

Histone

(HIS-tohn) A type of protein found in chromosomes; DNA wraps around histones.

Hormone

A chemical messenger that affects processes in the body such as growth and development, turning food into energy, sexual function and reproduction, and mood. Hormones are made in one part of the body and travel through the bloodstream to tissues and organs. Examples include insulin, estrogen, and testosterone.

Hydrocarbon

An organic molecule consisting of hydrogen and carbon atoms only.

I

Immune response

When immune cells, also known as white blood cells, find antigens and prompt the body to make antibodies to fight the infection.

Immune system

A network of cells, tissues, and organs that work together to protect the body from infection.

Immunology

The branch of biology and medicine dealing with the immune system.

Immunomodulator

(im-yoo-noh-MAH-juh-LAY-tur) A substance that stimulates or suppresses the immune system and may help the body fight cancer, infection, or other diseases.

Immunotherapy

(im-yoo-noh-THAYR-uh-pee) A medical treatment to stimulate or suppress a patient's immune system to help the body fight disease. Health care providers can use immunotherapy to treat patients with cancer or after an organ transplant, among other uses.

Imprinting

When a gene may be expressed differently in an offspring depending on the sex of the parent who passed on the gene.

Inflammation

The body's response to infection or injury, causing redness, swelling, heat, and pain.

Inhibitor

A molecule that "inhibits," or blocks, the biological action of another molecule.

Inorganic

Referring to a substance not derived from a living organism and/or not composed of carbon and hydrogen. Opposite of organic.

Insult

An injury to the body or a body part, or something that causes or could potentially cause such injury.

Invertebrate

The group of animals that don’t have a backbone. Examples include flies, worms, jellyfish, spiders, clams, and snails.

Ion

An electrically charged atom.

Isotope

(AHY-suh-tohp) A form of a chemical element that contains the same number of protons but a different number of neutrons than other forms of the element. Researchers often use isotopes to trace atoms or molecules in a metabolic pathway.

L

Lipid

Any of a diverse group of organic compounds that don't dissolve in water. Lipids include fats and oils, phospholipids (large components of cell membranes), waxes, and steroids (including cholesterol, a precursor to many hormones).

Lipoprotein

A substance containing both proteins and lipids. Insoluble ones are found in cell membranes. Soluble ones are found in blood and transport hydrophobic lipids, such as cholesterol , through the body.

Liposome

(LAHY-puh-sohm) An oily, microscopic capsule designed to package and deliver biological cargo, such as drugs, to cells in the body.

Lysosome

(LAHY-suh-sohm) A bubblelike organelle that contains powerful enzymes that break apart biological materials into nutrients and building blocks. Lysosomes also break apart waste and transport the waste to the outside of the cell.

M

Machine learning

An approach to artificial intelligence in which a computer algorithm (a set of rules and procedures) is developed to analyze and make predictions from data that is fed into the system. Machine learning-based technologies are routinely used every day, such as personalized news feeds and traffic prediction maps.

Mass spectrometry

(spek-TROM-ih-tree) An analytical technique used to determine the composition and abundance of the atoms in a molecular substance. Typical applications include dating of geologic samples; analysis of inorganic and organic chemicals, especially for small amounts of impurities; and determining the structural formula of complex organic substances.

Medicinal chemistry

An area of study involved with designing and making medicines for use in humans and animals.

Medicine

A type of drug—a chemical or biological molecule—that is regulated by the Food and Drug Administration (FDA) to diagnose, treat, or prevent specific health issues.

Meiosis

(mahy-OH-sis) The type of cell division that makes egg and sperm cells. Meiosis generates cells that are genetically different from one another and contain half the total number of chromosomes in the parent cell. The other type of cell division is mitosis.

Membrane

A semi-fluid layer of lipids and proteins. Membranes enclose cells and organelles and control passage of materials into and out of them.

Metabolic pathway

(met-uh-BOL-ik) A linked series of chemical reactions occurring within a cell that build up or break down organic molecules, releasing or using energy in the process, called metabolism.

Metabolism

The chemical changes that occur in a cell or an organism to break down a molecule, whether food, medicines, or biological substances, by enzymes. Metabolism produces energy and materials needed for growth and also gets rid of toxic substances. The product of a metabolic reaction is called a metabolite.

Metabolite

(muh-TAB-uh-lahyt) A substance made or used when the body breaks down food, drugs, or chemicals through metabolism .

Microarray

A technology used to study the expression of many genes at once. A scientist places thousands of gene sequences in known locations on a glass slide called a gene chip. A sample containing DNA or RNA is placed in contact with the gene chip. Light is produced to show genes expressed in the sample.

Microbiology

The branch of biology dealing with the study of microorganisms.

Microbiome

(mahy-kroh-BAHY-ohm) The genomes of the microbiota.

Microbiota

(mahy-kroh-bahy-OH-duh ) The community of microorganisms (bacteria, fungi, and viruses) found in a living organism.

Microorganism

An organism that can be seen only with the aid of a microscope and is usually just a single cell.

MicroRNA

A short piece of RNA that binds to messenger RNA, blocking its ability to make proteins.

Microscopy

A technique used to visualize objects with a microscope. The microscope creates a magnified image by directing a beam of light at the object and through one or a series of lenses. The image is in color and can be observed with the eye directly or recorded as a photo or video.

Mitochondrion

(mahy-tuh-KON-dree-uhn) (plural: mitochondria) The cell's power plant; the organelle that converts food and oxygen into energy to fuel the cell. Mitochondria contain their own small genomes and appear to have descended from free-living bacteria.

Mitosis

(mahy-TOH-sis) The type of cell division that eukaryotic cells use to make new body cells. Mitosis results in two daughter cells that are genetically identical to the parent cell. The other type of cell division is meiosis.

Model organisms

A small group of research organisms that help us understand the biology of humans. Examples include yeast, fruit flies, worms, zebrafish, and mice.

Molecular

Molecular describes things related to, consisting of, or produced by molecules.

Molecular modeling

The study of molecular structures, their chemical and physical characteristics, and their behaviors in different environments using theoretical and computational techniques.

Molecular target

The molecule researchers design a drug to bind to, producing therapeutic effects. Often, these molecules are receptors, and the drug can be an agonist that activates the receptor or an antagonist that blocks the receptor.

Molecule

The smallest unit of matter that retains all of the physical and chemical properties of that substance. It consists of one or more identical atoms or a group of different atoms bonded together. For example, a water molecule contains two hydrogen atoms and one oxygen atom.

Mutation

A variant, or DNA change, in an organism. In humans, usually refers to a disease-causing change.

Myelin

(MAHY-uh-lin) A fatty covering that protects nerve fibers and makes nerve signals move quickly through the nervous system.

N

Nanoparticle

A particle that is less than 100 nanometers (one-billionth of a meter) in all dimensions. They can be used as drug delivery systems for the targeted delivery and/or controlled release of drugs, such as antibodies, imaging agents, and cancer treatments, throughout the body. Also called nanomaterials.

Nanotechnology

(NAN-uh-tek-nol-uh-jee) Study of the control of matter on an atomic and molecular scale. A nanometer is one-billionth of a meter, or about the circumference of a marble in comparison to that of the Earth. Researchers can use nanotechnology across many fields of science, such as chemistry, biology, physics, and materials science.

Natural product

A molecule produced by a living organism—a plant, marine organism, or mic roorganism—that often has a medicinal us e.

Necrosis

(neh-KROH-sis) Cell death caused by trauma or infection. One other type of cell death is called apoptosis.

Neoblast

A type of stem cell. Neoblasts are found throughout the planarian worm anatomy and are responsible for regeneration.

Nerve cell

A cell in the nervous system that carries information through elec trical impulses and chemical messengers. Also called a neuron.

Neurotransmitter

(nyoor-oh-TRANS-mit-ur) A chemical messenger that passes signals between nerve cells or between a nerve cell and another type of cell.

NSAID

Non-steroidal anti-inflammatory drug, such as aspirin or ibuprofen, that reduces pain and inflammation.

Nuclear envelope

(NOO-klee-ur) A barrier that encloses the nucleus of a cell and controls the passage of molecules between the nucleus and cytoplasm. For example, RNA molecules made in the nucleus need to be passed into the cytoplasm for protein synthesis.

Nuclear magnetic resonance (NMR) spectroscopy

(NOO-klee-ur mag-NET-ik REZ-uh-nuhns spek-TROS-kuh-pee) A technique used to determine the detailed, three-dimensional structure of molecules and, more broadly, to study the physical, chemical, and biological properties of matter. It uses a strong magnet that interacts with the natural magnetic properties in atomic nuclei.

Nucleic acids

(noo-KLAY-ik): Large biomolecules that are essential in cells and viruses to store and express genomic information. Deoxyribonucleic acid (DNA) encodes the information cells need to make proteins. Ribonucleic acid (RNA) comes in different forms that play multiple cellular roles, including protein synthesis.

Nucleotide

(NOO-klee-uh-tahyd) A building block of DNA or RNA. It includes one base, one phosphate molecule, and one sugar molecule (deoxyribose in DNA, ribose in RNA). Thousands of nucleotides bind together to form a molecule of DNA or RNA.

Nucleus

(NOO-klee-uhs) (plural: nuclei) Biology: The membrane-bound structure within a eukaryotic cell that contains most of the cell's genetic material. Chemistry: The positively charged core of an atom, consisting of protons and neutrons.

O

Oocyte

(OH-uh-sahyt) The developing female reproductive cell; an immature egg.

Organ

A group of cells and tissues that perform a specific job, including the heart, brain, kidneys, liver, and lung.

Organelle

(Ohr-guh-NEL) A specialized structure that has a defined function in the cell. Organelles include the nucleus, mitochondria, Golgi, endoplasmic reticulum (ER), and lysosomes.

Organic

Referring to carbon-containing compounds that are the basis for all living organisms. Opposite of inorganic.

Organism

An individual animal, plant, or single-celled life form.

Organogenesis

The production and development of the organs of an animal or plant.

Organoid

(OHR-guh-noyd): A 3D, mini-organ-like structure made by growing stem cells in the laboratory. They contain many types of cells and closely mimic the structure, organization, and some of the functions of human tissues and organs. They’re used to study how tissues form and respond to certain conditions or drugs.

Organometallic

Referring to a substance containing a metal atom bonded to an organic atom or atoms (usually carbon).

Organ-on-chip

A system containing human cells or tissues grown inside a microfluidic chip. They mimic the structure and function of different organs and can be used for drug development, disease modeling, and personalized medicine. Also called tissue chips.

P

Pathogen

A bacterium, virus, or other microorganism that can cause disease.

Pathway

A series of actions among molecules in a cell that leads to a certain product or change within that cell, such as spurring cell movement, assembling new molecules, or turning genes on and off.

Peptide

(PEP-tahyd) A molecule consisting of a chain of amino acids; a small protein fragment.

Peripheral nervous system

(puh-RIF-ur-uhl) The part of the nervous system outside of the central nervous system—the bra in and spine.

Pharmacodynamics

(fahr-muh-koh-dahy-NAM-iks) A branch of pharmacology studying how drugs act on their molecular targets and on the organs and tissues in the body.

Pharmacogenetics

(fahr-muh-koh-juh-NET-iks) The study of how people's genes affect their bodies’ responses to medicines, often one gene at a time.

Pharmacogenomics

(fahr-muh-koh-jee-NOHM-iks) The study of how people's genes affect their bodies’ responses to medicines, often encompassing the entire genome.

Pharmacokinetics

(fahr-muh-koh-kih-NET-iks) A branch of pharmacology studying the level of a drug and its breakdown products in the blood over time.

Pharmacology

(fahr-muh-KOL-uh-jee) The study of how molecules from outside the body interact with organ systems, for example in cell signaling and communications.

Phenotype

(FEE-nuh-tahyp): An individual’s observable traits, such as eye color, height, and blood type. Some phenotypic traits are largely determined by environmental factors, but others are largely determined by the individual’s genes. The genetic contribution to the phenotype is called the genotype.

Phospholipid

(fos-foh-LIP-id) A type of lipid molecule made up of two fatty acids, a phosphate group (phosphorous and oxygen), and glycerol (a type of alcohol). Fatty acids are long chains containing mostly hydrogen and carbon. The phosphate “head” of a phospholipid attracts water while the fatty acid chains repel water, so the molecules line up in a double layer with phosphate groups on the outside and fatty acids on the inside to form membranes.

Photosynthesis

A natural process where green plants, algae, and some bacteria use the sun's energy to make carbohydrates from carbon dioxide and water. The carbohydrates are then broken down to produce energy, allowing the plant to grow.

Physical trauma

A serious injury to the body, such as the following:

• Blunt-force trauma: When an object or force strikes the body, often causing concussions, deep cuts, or broken bones
• Penetrating trauma: When an object pierces the skin or body, usually creating an open wound

Surgery can also cause physical trauma, sometimes called a controlled injury.

Physiology

(fiz-ee-OL-uh-jee) The study of how living organisms function.

Plasma membrane

A double layer of phospholipids with embedded proteins that separates the conten ts of a cell from its outside environment.

Polymer

(POL-uh-mur) A large molecule formed by combining small molecules in a simple repeating pattern.

Polysaccharide

(PAH-lee-SAK-uh-rahyd) A larg e carbohydrate molecule; also called glycan. Polysaccharides are made up of many small sugar molecules that are joined chemically.

Precision medicine

An emerging approach for disease prevention and treatment that takes into account individual differences in lifestyle, environment, and biology.

Prokaryotic cell

(proh-KAYR-ee-oh-tik) A cell that lacks a nucleus, such as a bacterium.

Proteasome

(PRO-tee-uh-zohm) A cellular machine that breaks down proteins that are no longer needed and recycles or removes the resulting molecules.

Protein

A large, biological molecule composed of amino acids. Proteins are essential for all life processes. They are arranged in a specific order determined by the genetic code and folded into a specific three-dimensional shape with well-defined structures. Protein structures include alpha helixes, short, spiral-shaped sections, and beta sheets, pleated sections.

Protein synthesis

The process the body uses to create proteins from amino acids in the cell’s ribosomes.

• Trans cription : The first step, in which the information coded in DNA is copied (transcribed) into mRNA
• Translation: The second step, in which the information encoded in mRNA is us ed to build the right sequence of amino acids

Proteome

(PROH-tee-ohm) The complete set of proteins made by an organism . Studying the proteome may lead to a better understanding of which proteins are involved in specific diseases or how medicines could be developed to target proteins and treat disease.

Proteomics

(proh-tee-OM-iks) The systematic, large-scale study of all proteins in an organism.

Q

Qualitative

Descriptive; based on interpretation and observations. Qualitative data helps researchers understand the why and how behind certain behaviors, but it is subjective and unique—unlike quantitative data.

Quantitative

Numbers-based, countable, or measurable. Quantitative data tells researchers how many, how much, or how often through calculations and nu mbers. It is fixed and universal, unlike qualitative data.

R

Radiation

Energy that comes from a source at the speed of light in the form of waves with an electric field and a magnetic field. Also called electromagnetic waves.

Radioactive

Giving off radiation, often through the spontaneous release of energy from an unstabl e atom to get to a more stable state.

Reagent

A substance that reacts with another in a chemical reaction. It can be used to test for the presence of another substance by causing a chemical reaction with it.

Receptor

A protein found on the cell surface to which a signal molecule attaches. This leads to a cascade of reactions involving several other molecules inside the cell. Specific signal molecules bind to specific receptors, fitting together like a key in a lock. Many medicines target receptor proteins, either triggering a response (agonist) or preventing a response (antagonist).

Recombinant DNA

(ree-KOM-buh-nuhnt) Hybrid DNA produced in the lab by joining pieces of DNA from different sources.

Regeneration

Regeneration is the natural process of replacing or restoring damaged or missing cells, tissues, organs, and even entire body parts to full function in plants and animals.

Replication

(rep-li-KAY-shuhn) The process by which a DNA molecule is copied to make two identical DNA molecules. This process is essential for cell division so that each of the two daughter cells receives the exact same genetic information as the original parent cell.

Research organism

Any creature that scientists use to study life. Examples range from single-celled organisms such as bacteria to more complex ones such as mice.

Ribosome

(RAHY-buh-sohm) A molecular complex in which proteins are made. It’s composed of proteins and ribosomal RNA.

RNA (ribonucleic acid)

(RAHY-buh-noo-clay-ik) A long, usually single-stranded chain of nucleotides. There are three major types of RNA, which are all involved in protein synthesis:

• Messenger RNA (mRNA) is complementary to one of the DNA strands of a gene and carries genetic information to the ribosome for protein synthesis.
• Transfer RNA (tRNA) works with mRNA to make sure the right amino acids are inserted into the protein being made.
• Ribosomal RNA (rRNA) (RAHY-buh-sohm-uhl), together with proteins, makes up ribosomes and functions to recognize the mRNA and tRNA that are presented to the ribosomal complex.

Certain viruses contain RNA, instead of DNA, as their genetic material.

RNA polymerase

(POL-uh-muh-rays) An enzyme that makes RNA using DNA as a template in a process called transcription.

RNA splicing

When noncoding pieces of RNA, called introns, are removed and coding pieces of RNA, called exons, are joined together to produce an mRNA molecule.

RNAi (RNA interference)

A naturally occurring process in which small pieces of double-stranded RNA are used to prevent translation of messenger RNA. The process occurs in many organisms to silence genes when their protein products are no longer needed. When RNAi doesn’t work as it should, it may lead to certain diseases. RNAi has an important role in basic research allowing scientists to directly observe the effects of the loss of function of specific genes.

S

Sepsis

A person’s overwhelming or impaired whole-body immune response to an insult—an infection or an injury to the body, or something else that provokes such a response. Most sepsis is caused by bacterial infections, but it can also be caused by viral infections, such as COVID-19 or influenza; fungal infections; or noninfectious insults, such as traumatic injury.

Side effect

The effect of a drug, other than the desired effect, sometimes in an organ other than the target organ.

Signal transduction

(tranz-DUHK-shuhn) When chemical, electrical, or biological signals are transmitted into and within a cell.

Stem cell

A cell that can develop into many different cell types in the body. When stem cells divide, they can form more stem cells or other specialized cells.

• Adult stem cells: Cells found throughout the body that replace tissue damaged by disease, injury, or age
• Embryonic stem cell (em-bree-ON-ik): A cell found in early embryos that can become any kind of cell in the body
• Induced pluripotent stem cells (iPSC) (ploor-uh-POHT-nt): Specialized tissue or organ cells that have been reprogrammed in a lab into a stem cell-like state and can become just about any cell type

Structural biology

The study of how biological molecules are built. Imaging techniques allow scientists to view molecules in three dimensions to see how they are put together, how they function, and how they interact.

Substrate

A molecule that binds to an enzyme and undergoes a chemical change during the ensuing reaction.

Symbiosis

A relationship between members of any two unrelated species. Symbiotic relationships are defined by how the members benefit from the relationship.

• Mutualistic: Both organisms benefit from their interaction.
• Commensal: One organism benefits from the interaction while the other is not helped nor harmed.
• Parasitic: One organism benefits from the interaction while the other is harmed.

Synchrotron

(SING-kruh-tron) A large machine that accelerates electrically charged particles to nearly the speed of light and maintains them in circular orbits. Originally designed for use by high-energy physicists, synchrotrons are now heavily used by structural biologists as a source of very intense X-rays.

Synthetic

Made by chemical synthesis, often to imitate a natural product or to form more complex chemical molecules from simpler building blocks.

Systems biology

A field focused on the study of relationships and interactions between various parts of a biological system (metabolic pathways, organelles, cells, and organisms) and that integrates this information to understand how biological systems function.

T

Telomerase

(tuh-LOM-uh-rays) An enzyme that adds a repetitive segment of DNA, or telomere, to the ends of chromosomes, so the chromosomes don’t shrink during each cell division.

Tissue

A group of cells that act together to carry out a specific function in the body. Examples include muscle tissue, nervous system tissue (including the brain, spinal cord, and nerves), and connective tissue (including ligaments, tendons, bones, and fat). Organs are made up of tissues.

Tissue engineering

A field of study that combines cells, engineering, and materials methods, with the goal of improving or replacing biological functions.

Transcription

(tran-SKRIP-shun): The process of making an RNA copy of a piece of DNA. This copy, called messenger RNA (mRNA), carries th e genetic information needed to make proteins in a cell. It leaves the cell nucleus and enters the cytoplasm, where it directs protein synthesis.

Translation

The process of making proteins based on genetic information encoded in messenger RNA. Translation occurs in ribosomes.

Transmission electron microscopy (TEM)

The most powerful type of electron microscopy (EM), which uses electrons to create an image of a sample. TEM can magnify objects more than 10 million times, making the outline and some details of cells, viruses, and even some large molecules visible.

U

Ubiquitin

(yoo-BIH-kweh-tin) A small protein that attaches to and marks other proteins for the proteasome to destroy.

V

Variant

A permanent change in a DNA sequence that makes up a gene. Variants in genes can cause disease, affect fetal development, or result in differences in how people’s bodies look or work; but they may not cause disease or have any effect at all. Exposure to some types of radiation, chemicals, or viral infections can produce variants; or they can be generated during cell division or DNA replication. Variants in egg or sperm cells can be passed on to offspring, while those in body cells aren't passed on. The term mutation has often been used to describe a disease-causing variant. Related to genetic variation.

Variation

tabindex="-1">variants influence biological function, while others have no biological effects.

Vertebrate

The group of animals that have a spine/backbone inside their body. Examples include mammals, fish, reptiles, an d birds.

Vesicle

(VES-ih-kuhl) A small, membrane-bounded sac that transports substances between organelles as well as to and from the cell membrane.

Virus

An infectious agent composed of proteins and genetic material (either DNA or RNA) that requires being in a host cell, such as a plant, animal, or bacterium, in order to reproduce. A virus is neither a cell nor a living organism because it can't reproduce on its own.

X

X-ray crystallography

(kris-tl-OG-ruh-fee) A technique used to determine the detailed, three-dimensional structure of molecules. It’s based on the scattering of X-rays through a crystal of the molecule under study.

X-ray free electron laser

A tool that uses beams of fast-moving electrons to determine the 3D structures of molecules. Unlike conventional electron lasers, it uses unbound, or “free,” electrons accelerated to produce X-ray radiation. It can capture chemical processes while they’re taking place.

Y

Yeast

A type of microorganism commonly used to make fermented foods (bread, cheese, alcoholic drinks, etc.) that is also often used as a research organism because of its ease of manipulation during experiments, its similarity to human cells, and its rapid growth rate.

Z

Zygote

(ZAHY-goht) A cell resulting from fusing an egg and a sperm.