A
AAA ATPase family A group of proteins that couple hydrolysis of ATP with large molecular movements usually associated with unfolding of protein substrates or the disassembly of multisubunit protein complexes.
ABC superfamily A large group of integral membrane proteins that often function as ATP-powered membrane transport proteins to move diverse molecules (i.e., phospholipids, cholesterol, sugars, ions, peptides, etc.) across cellular membranes.
Acetyl CoA The entry compound for the Krebs cycle in cellular respiration; formed from a fragment of pyruvate attached to a coenzyme.
Acetylcholine One of the most common neurotransmitters; functions by binding to receptors and altering the permeability of the postsynaptic membrane to specific ions, either depolarizing or hyperpolarizing the membrane.
Acid A substance that has a pH below 6.99 and that increases the hydrogen ion concentration in a solution.
Acrosome An organelle at the tip of a sperm cell that helps the sperm penetrate the ovum’s outer membrane.
Actin A globular protein that links into chains, two of which twist helically about each other, forming microfilaments in a muscle and other contractile elements in cells.
Action potential Rapid, transient, all-or-none electrical activity propagated in the plasma membrane of excitable cells (i.e., neurons and muscle cells) as the result of the selective opening and closing of voltage-gated Na+ and K+ channels.
Activation energy The input of energy required to (overcome the barrier to) initiate a chemical reaction. By reducing the activation energy, an enzyme increases the rate of a reaction.
Activator Specific transcription factor that stimulates transcription.
Active site Specific region of an enzyme that binds a substrate molecule and promotes a chemical change in the bound substrate.
Active transport The movement of a substance across a biological membrane against its concentration or electrochemical gradient, with the help of energy input and specific transport proteins or an electrochemical gradient driven by the coupled hydrolysis of ATP.
Adaptive peak An equilibrium state in a population when the gene pool has allele frequencies that maximize the average fitness of a population’s members (i.e., eugenics).
Adenosine Triphosphate (ATP) See ATP
Adenylyl cyclase One of several enzymes that is activated by the binding of certain ligands to their cell-surface receptors and catalyzes formation of cyclic AMP (cAMP) from ATP; also called adenylate cyclase.
Adhesion receptor Protein in the plasma membrane of animal cells that binds components of the extracellular matrix, thereby mediating cell-matrix adhesion. The “integrins” are major adhesion receptors.
Adrenal gland An endocrine located adjacent to the kidney in mammals; composed of two separate glandular zones; an outer cortex, which responds to endocrine signals in reacting to stressors and effecting salt and water balance; and a central medulla, which responds to nervous inputs resulting from stressors.
Aerobic Containing oxygen; referring to an organism, environment, or cellular respiratory processes that require oxygen.
Aerobic oxidation Oxygen-requiring metabolism of sugars and fatty acids to CO2 and H2O coupled to the synthesis of ATP.
Agonist A molecule, often synthetic, that mimics the biological function of a natural molecule (i.e., hormones, etc.)
AIDS (acquired immunodeficiency syndrome) The name designation of the “mutated” or late stages of HIV infection; defined by a specific reduction of T cells and the appearance of characteristic secondary infections.
Aldehyde An organic molecule with a carbonyl group located at the end of the carbon skeleton.
Aldosterone An adrenal hormone that acts on the distal tubules of the kidney to stimulate the reabsorption of sodium (Na+) and the passive flow of water from the filtrate.
Alga (pleural, algae) A photosynthetic, plant-like protist.
Allantois One of four extra-embryonic membranes; serves as a repository for the embryo’s nitrogenous waste.
Allele One of two or more alternative forms of a gene. Diploid cells contain two alleles of each gene, located at the corresponding site (locus) on homologous chromosomes.
Allometric growth The variation in the relative rates of growth of various parts of the body, which helps to shape the organism.
Allosteric site A specific receptor site on an enzyme molecule remote from the active site. Molecules bind to the allosteric site and change the shape of the active site, making it either more or less receptive to the substrate.
Allostery Change in the tertiary and/or quaternary structure of a protein induced by binding of a small molecule to a specific regulatory site, causing a change in the protein’s activity.
Alpha (a) carbon atom (C ) In amino acids, the central carbon atom that is bonded to four different chemical groups (except in glycine) including the side chain, or R group.
Alpha (a) helix A spiral shape constituting one form of the secondary structure of proteins, arising from a specific hydrogen-bonding structure.
Alternative splicing Process by which the exons of one pre-mRNA are spliced together in different combinations, generating two or more different mature mRNAs from a single pre-mRNA.
Alveolus (pl. alveoli) One of the dead end (cul-de-sac), multilobed air sacs that constitute the gas exchange surface of the lungs; one of the milk-secreting sacs of epithelial tissue in the mammary glands.
Amino acid An organic molecule possessing both carboxyl and amino groups. Amino acids serve as the monomers or “building blocks” of proteins.
Amino group A functional group that consists of a nitrogen atom bonded to two hydrogen atoms; can act as a base in solution, accepting a hydrogen ion and acquiring a charge of + 1.
Aminoacyl-tRNA Activated form of an amino acid, used in protein synthesis, consisting of an amino acid linked via a high-energy ester bond to the 3’-hydroxyl group of a tRNA molecule.
Aminoacyl-tRNA synthetases A family of enzymes, at least one for each amino acid, that catalyze the attachment of an amino acid to its specific tRNA molecule.
Amniocentesis A technique for determining abnormalities in a fetus by the presence of certain chemicals or defective fetal cells in the amniotic fluid, obtained by aspiration from a needle trans-dermally inserted into the uterus.
Amnion The innermost of four extraembryonic membranes; encloses a fluid-filled sac in which the embryo is suspended.
Amniotic egg A shelled, water-retaining egg that enables reptiles, birds and egg-laying mammals to complete reproductive cycles outside their body on dry land.
Anabolism A process in which energy is employed to support the synthesis of complex molecules from simpler compounds.
Anaerobic Lacking oxygen; referring to an organism, environment, or cellular process that lacks oxygen and may be damaged, growth inhibited or killed by its presence.
Anaphase Mitotic stage during which the sister chromatids (or duplicated homologues in meiosis I) separate and move apart (segregate) toward the spindle poles.
Anchoring junctions Specialized regions on the cell surface containing cell-adhesion molecules or adhesion receptors; include adherens junctions and desmosomes, which mediate cell-cell adhesions, and hemidesmosomes, which mediate cell-matrix adhesion.
Androgens The principal male steroid hormones, such as testosterone, which stimulate the development and maintenance of the male reproductive system and secondary sex characteristics.
Aneuploidy A chromosomal aberration in which certain chromosomes are present in extra copies (e.g., Downs syndrome) or are deficient in number, which deviates from the normal diploid number of chromosomes.
Anion A negatively charged ion.
Antagonist A molecule, often times synthetic, that blocks the biological function of a natural molecule (for instance, hormones, etc.).
Antibiotic A chemical that kills bacteria or inhibits their growth.
Antibody An antigen-binding immunoglobulin, produced by B cells. that functions as the effector in an immune response.
Anticodon A specialized base triplet on one end of a tRNA molecule that recognizes a particular complementary codon on an mRNA molecule.
Antidiuretic hormone (ADH) A hormone important in osmoregulation .
Antigen A foreign macromolecule that does not belong to the host organism and that elicits an immune response. For B cells, an antigen elicits formation of antibody that specifically binds the same antigen; for T cells, an antigen elicits a proliferative response, followed by production of cytokines or the activation of cytotoxic activity.
Antigen-presenting cell (APC) Any cell that can digest an antigen into small peptides and display the peptides in association with class II MHC molecules on the cell surface where they can be recognized by T cells. Professional APCs (i.e., dendritic cells, macrophages, and B cells) constitutively express class II MHC molecules.
Antiport A type of cotransport in which a membrane protein (antiporter) transports two different molecules or ions across a cell membrane in opposite directions.
Apoptosis Programmed cell death brought about by signals that trigger the activation of a cascade of “suicide” proteins in the cells programmed to die.
Apoptosome Large disc-shaped heptamer of mammalian Apaf-1, a protein that assembles in response to apoptosis signals and serves as an activation machine for initiator and effector caspases.
Aqueous solution A solution in which water is the solvent.
Arteriosclerosis A cardiovascular inflammatory disease characterized by the formation of inner lining hard plaques of mixed substances (e.g., Ca, fibrin, saturated fats, cholesterol, etc.).
Artery A muscular-walled blood vessel that carries blood away from the heart to cells, tissues and organs throughout the body.
Artificial selection (i.e., selective breeding, eugenics, etc.)The selective breeding of plants, animals and humans to encourage the concentration of specific desirable traits.
Assortive mating A type of nonrandom mating in which mating partners resemble each other in certain phenotypic characteristics.
Atomic number The number of protons in the nucleus of an atom, unique for each element and designated by a subscript to the left of the elemental symbol.
Atomic weight The total atomic mass, which is the mass in grams of one mole of the atom.
ATP (adenosine triphosphate) An adenine-containing nucleotide triphosphate that releases free energy when its phosphate bonds are hydrolyzed. This energy is used to drive endergonic reactions in cells.
ATPase One of a large group of enzymes that catalyze hydrolysis of ATP to yield ADP and inorganic phosphate with the release of free energy.
ATP synthase A cluster of several multimeric membrane proteins found in the mitochondrial cristae (thylakoid membranes of chloroplasts and bacterial plasma membrane) that function in chemiosmosis with adjacent electron transport chains, using the energy of a hydrogen-ion concentration gradient to make ATP. ATP synthases provide a port through which hydrogen ions diffuse into the matrix of a mitochondrion.
Atrioventricular valves Valves in the heart that guard the divide between each atrium and ventricle to prevent a backflow of blood each time the ventricles contract.
Atrium The upper two chambers of the heart that receive venous blood returning to the heart.
Autocrine Referring to signaling mechanism in which a cell produces a signaling molecule (e.g., growth factor) and then binds and responds to it.
Autoimmune disease An immunological disorder in which an individual’s own immune system turns against itself.
Autosome A chromosome that is not directly involved in determining gender, as opposed to the sex chromosomes.
Autonomic nervous system A subdivision of the motor nervous system of vertebrates that regulates the internal environment. It consists of the sympathetic and parasympathetic divisions.
Axon A typically long extension, or process, that extends from a neuron that carries nerve impulses away from the cell body toward target cells.
Axoneme Bundle of microtubules and associated proteins present in cilia and flagella and responsible for their structure and movement.
B
B cell A type of lymphocyte that develops in the bone marrow, is activated in the appendix and later produces antibodies, which in turn mediate humoral immunity. After interacting with antigen, a B cell proliferates and differentiates into antibody-secreting plasma cells.
Bacteria One of two prokaryotic domains, (i.e., Domain Bacteria) the other being the Archaea.
Bacteriophage (phage) Any virus that infects bacterial cells. Some phages are widely used as vectors in DNA cloning.
Barr body A dense structure lying along the inside of the nuclear envelope in female mammalian cells, representing an inactivated X chromosome.
Base Any compound, often containing nitrogen, that can accept a proton (H+) from an acid. Also, commonly used to denote the purines and pyrimidines in DNA and RNA.
Base pair Association of two complementary nucleotides in a DNA or RNA molecule stabilized by hydrogen bonding between their base components. Adenine pairs with thymine or uracil (e.g., A-T, A-U) and guanine pairs with cytosine (G-C).
Benign A non-malignant tumor that is made up of cells that are similar to normal cells – benign tumors and benign tumor cells remain in the tissue in which they originate, however, on occasion by occupying space they can present a clinical problem.
Beta sheet A flat secondary structure in proteins that is created by hydrogen bonding between the backbone atoms in two different polypeptide chains or segments of a single folded chain.
Beta turn A short U-shaped secondary structure in proteins.
Binary fission The type of cell division by which prokaryotes reproduce; each dividing daughter cell receives a copy of the single parental chromosome.
Biosphere The entire portion of Earth that is inhabited by some form of life; the sum of all the planet’s communities and ecosystems.
BLAST A commonly used computer program for comparing the amino acid sequence of a protein with the sequences of known proteins stored in data bases. The BLAST program searches can provide insight into the structure, function and evolution of newly discovered proteins.
Blastocyst Stage of mammalian embryo produced in one week after fertilization in humans and is composed of =64 cells that have separated into two cell types: trophectoderm, which will form extra-embryonic tissues, and the inner cell mass, which gives rise to the embryo, the stage that implants into the uterine wall and corresponds to the blastula of other animal embryos.
Blastula The hollow ball of cells marking the end stage of cleavage during early embryonic development.
C
Calcitonin A mammalian thyroid hormone that lowers blood calcium levels.
Calorie A unit of heat (thermal energy). One calorie is the amount of heat required to raise the temperature of one gram of water by one degree centigrade; the amount of heat energy that 1 g of water releases when it cools by one degree centigrade. The Calorie (with a capital C) usually used to denote the energy content of a food is referred to as a kilocalorie.
Calvin cycle The primary metabolic pathway that “fixes” CO2 into carbohydrates during photosynthesis; also known as carbon fixation.
Cambrian explosion A burst of evolutionary origins when most of the major body plans of animals appeared in a relatively brief time in geological history (Creation?); recorded in the fossil record about 545 to 525 million years ago.
Cancer A generic word used to describe many types of non-genetically transmitted malignant tumors, the cells of which grow and divide more rapidly than normal cells, they invade surrounding tissue and can metastasize to other sites, tissues and organs.
Capsid The outer proteinaceous coating of a virus, formed by multiple copies of one or more protein subunits, and enclosing the viral nucleic acid.
Carotenoids A form of pro-vitamin A; accessory pigments, yellow and orange, found in the chloroplasts of plants; by absorbing wavelengths of light that chlorophyll cannot, they broaden the spectrum of colors that can drive photosynthesis.
Carbohydrate Broad term for certain non-essential polyhydroxyaldehydes, polyhydroxyketones, and or compounds derived from these carbon chains having the formula (CH2O)n.
Carcinogen Any food state (trans fatty acid, heterocyclic amine, and acrylamide), chemical or physical agent that can initiate/cause a malignant tumor (cancer) when cells, tissues, organs and organisms are exposed to it.
Caretaker gene Any gene whose encoded protein that cooperates in the protection of the integrity of the individuals genome by participating in the repair of damaged DNA. Loss of function of a caretaker gene, as a result of nutritional deficiencies and or contact with carcinogens, leads to increased mutation rates and promotes carcinogenesis.
Carrier (genetic) In classic vertebrate genetics, an individual who is heterozygous at a given genetic locus, with one normal dominant allele and one a potentially harmful recessive allele. The heterozygote is phenotypically normal for the character determined by the normal dominant allele, however, they can pass on the recessive harmful allele to the offspring.
Caspases A class of vertebrate protein-degrading enzymes (proteases) that are required for the process of programed cell death (apoptosis) and work in a cascade with each form activating the following form.
Catabolism Cellular degradation of complex molecules to simpler compounds that produce a release of energy.
Catalyst A substance that increases the rate of speed or efficiency of a reaction without a permanent change of its structure. Enzymes are proteins with catalytic activity—ribozymes are RNAs that can function as catalysts.
Cation A positively charged ion.
cDNA (complementary DNA) DNA copied from an mRNA molecule by reverse transcriptase and therefore lacking the introns present in the DNA of the individuals genome.
Cell-adhesion molecules (CAMs) Proteins in the plasma membrane of cells that bind with similar proteins on other cells, thereby mediating cell–cell adhesion. Four major classes of CAMs include the cadherins, IgCAMS, integrins, and selectins.
Cell cycle The ordered sequence of events in which a eukaryotic cell duplicates its chromosomes and divides into two daughter cells. The typical cell cycle consists of four phases: G1 before DNA synthesis occurs; S when DNA replication occurs; G2 after DNA synthesis; and M when cell division occurs, yielding two daughter cells. Under certain conditions, cells leave the cell cycle during G1 and remain in the Go state as non-dividing cells.
Cell division Separation of a cell into two daughter cells. In higher eukaryotes, it involves division of the of the nucleus (mitosis) and of the cytoplasm (cytokinesis); mitosis often is used to refer to both nuclear and cytoplasmic division.
Cell junctions Specialized regions on the cell surface through which cells are joined to each other or to the extracellular matrix.
Cell line A population of cultured cells, of plant or animal origin, that has undergone a genetic alteration allowing the cells to reproduce indefinitely (e.g., Hela cells).
Cell strain A population of cultured cells, of plant or animal origin, that has a finite life span and eventually dies out, typically after 25 to 50 generations (the “Hayflick limit”).
Cellular respiration The most prevalent and efficient catabolic pathway for the production of ATP, in which oxygen is consumed as a reactant along with the organic fuel.
Cellulose A structural polysaccharide made up of a chain of glucose units linked together by B(1-4) glycosidic bonds.
Cell wall A specialized, rigid extracellular matrix that lies next to the plasma membrane, protecting a cell and maintaining its shape; prominent in most fungi, plants, and prokaryotes, however, is absent in most multicellular animals.
Central nervous system (CNS) In vertebrate animals, the brain and spinal cord.
Centriole Either of two cylindrical structures within the centrosome of animal cells and containing nine sets of triplet microtubules; structurally similar to a basal body.
Centromere DNA sequence required for proper segregation of chromosomes during mitosis and meiosis; the region of mitotic chromosomes where the kinetochore forms and that appears constricted.
Centrosome (cell center) Structure located near the nucleus of animal cells that is the primary microtubule-organizing center (MTOC); it contains a pair of centrioles embedded in a protein matrix and duplicates before mitosis, with each centrosome becoming a spindle pole.
Cerebellum Part of the vertebrate hindbrain (rhombencephalon) located dorsally; functions in unconscious coordination of movement and balance.
Cerebral cortex The surface of the cerebrum; the largest and most complex part of the mammalian brain, containing sensory and motor nerve cell bodies of the cerebrum; the part of the vertebrate brain most changed through evolution.
Cerebrum The dorsal portion, composed of right and left hemispheres, of the vertebrate forebrain; the integrating center for memory, learning, emotions, and other highly complex functions of the central nervous system.
Chemical equilibrium The state of a chemical reaction in which the concentration of all products and reactants is constant because the rates of the forward and reverse reactions are identical.
Chemical potential energy The energy stored in the bonds connecting atoms in molecules.
Chemiosmosis Process where an electrochemical proton gradient (pH plus electric potential) across a membrane is used to drive an energy-requiring process (i.e., ATP synthesis).
Chemokine A variety of small, secreted proteins that function as chemotactic cues for white blood cells.
Chemotaxis Movement of a cell or organism toward or in opposite directions from specific chemicals.
Chlorophylls A group of magnesium based light-absorbing green porphyrin pigments that are required for the process of photosynthesis.
Chloroplast A specialized organelle in plant cells that is surrounded by a double membrane and contains internal chlorophyll-containing membranes (thylakoids) where light-absorbing reactions of photosynthesis take place.
Cholesterol A lipid made up of the four-ring steroid structure with a hydroxyl group on one ring; a component of cell membranes, myelin, precursor of steroid hormones, bile acids and vitamin D.
Chondrin A protein-carbohydrate complex secreted by chondrocytes; chondrin and collagen fibers combine to form cartilage and other connective tissues.
Chorionic villus sampling A technique for diagnosing “genetic” and congenital defects while the fetus is in the uterus. A small sample of the fetal portion of the placenta is removed and analyzed.
Chromatid A single copy of a replicated chromosome, formed during the S phase of the cell cycle, that is joined at the centromere to the other copy; also called sister chromatid. During mitosis, the two chromatids separate, each becoming a chromosome of one of the two daughter cells.
Chromatin Complex of DNA, histones, and non-histone proteins from which eukaryotic chromosomes are formed. Condensation of chromatin during mitosis yields visible metaphase chromosomes.
Chromosome In eukaryotes, the structural unit of the genetic material consisting of a single, linear double-stranded DNA molecule and associated proteins. In most prokaryotes, a single, circular double-stranded DNA molecule constitutes the bulk of the genetic material.
Cilium Short, membrane enclosed structure protruding from the surface of eukaryotic cells and containing a core bundle of microtubules. Cilia usually occur in clusters and beat rhythmically to move a single cell organism or to move particles or fluid along a surface.
Cisterna Flattened membrane enclosed compartments such as the Golgi complex and endoplasmic reticulum.
Citric acid cycle A set of nine connected reactions that occur in the matrix of the mitochondria in which acetyl groups are oxidized, generating CO2 and reduced intermediates used to produce ATP; also referred to as the Krebs cycle and tricarboxylic acid (TCA) cycle.
Cleavage In embryogenesis, “cleavage” refers to the series of rapid cell divisions that occurs following fertilization and with little cell growth, producing progressively smaller cells; cleavage culminates in the formation of the blastocyst in mammals or blastula in other animals; also used for the hydrolysis of molecules.
Clone A population of genetically identical cells, viruses, or organisms that have descended from a common ancestor, or multiple identical copies of a gene or DNA fragment generated and maintained through DNA cloning.
Cochlea The spiral-shaped structure in the inner ear containing the organ of Corti, the sound sensing apparatus.
Condon Sequence of three nucleotides in DNA or mRNA that specifies a particular amino acid during protein synthesis; also called triplet. Of the 64 possible codons, three are stop codons, which do not specify amino acids and cause the termination of protein synthesis.
Collagen A triple-helical glycoprotein, rich in glycine and proline, that is a major component of the extracellular matrix and connective tissues. The numerous subtypes of collagen differ in their tissue distribution and the extracellular components and cell surface proteins with which they unite.
Complement A group of constitutive serum proteins that bind directly to microbial or fungal surfaces, thereby activating a proteolytic cascade that culminates in the formation of the cytolytic membrane attack complex.
Complementary Referring to two nucleic acid sequences or strands that can form perfect base pairs with each other, also describes regions on two interacting molecules (e.g., enzyme and its substrate) that physically interact as with a lock and key.
Concentration gradient In cell biology, refers to the difference in the concentration of a substance in different locations of a cell or embryo or on different sides of a cell membrane.
Cone cell One of two types of photoreceptors in the vertebrate eye—detects color during the day.
Contractile bundles Bundles of actin and myosin in non-muscle cells that are involved with cellular adhesion or cell movement.
Covalent bond Stable chemical force that holds the atoms in molecules together by the sharing of one or more pairs of electrons.
Crista An infolding of the inner membrane of a mitochondrion that houses the electron transport chain and the enzyme catalyzing the synthesis of ATP.
Crossing over Exchange of genetic material between maternal and paternal chromatids during meiosis to produce recombined chromosomes.
Cyclic AMP (cAMP) A second messenger, produced in response to hormonal stimulation of certain G protein-coupled receptors, that activates protein kinase A.
Cyclic GMP (cGMP) Cyclic adenosine monophosphate, a ring-shaped molecule made from ATP, a second messenger in eukaryotic cells, that open cation channels in rod cells and activates protein kinase G in vascular smooth muscle and a variety of other cells.
Cytochromes A group of pigmented, heme-containing proteins, some of which function as electron carriers during cellular respiration and photosynthesis in mitochondria and chloroplasts.
Cytokine Any of numerous small, macrophage and helper T cell secreted proteins (such as erythropoietin, G-CSF, interferons, interleukins, etc.) that bind to cell-surface receptors on blood and immune-system cells to initiate their differentiation or proliferation.
Cytokinesis The division of the cytoplasm following mitosis to form two daughter cells, each with their own nucleus and cytoplasmic organelles.
Cytoplasm The viscous contents of a cell that are contained in a plasma membrane and outside of the nucleus in eukaryotic cells.
Cytoskeleton The network of fibrous elements, consisting primarily of microtubules, microfilaments, and intermediate filaments, found in the cytoplasm of eukaryotic cells.
Cytosol The unstructured aqueous phase of the cytoplasm excluding organelles, membranes, and insoluble cytoskeletal structures.
D
Dalton Unit of molecular mass approximately equal to the mass of a hydrogen atom (1.66 x 10-24 g).
Darwinian fitness A measure of the relative contribution of an individual to the gene pool of the next generation.
Denaturation Drastic alteration in the conformation of a protein or nucleic acid due to the disruption of many noncovalent interactions caused by heat or the exposure to a variety of chemicals, which more often than not results in the loss of biological function.
Dendrite A short, branched projection that extends from the cell body of a neuron that receives chemical or electrical signals from the axons of other neurons.
Deoxyribonucleic acid DNA
Depolarization Decrease in the cytosolic-face negative electric potential that normally exists across the plasma membrane of a cell at rest, that results in a less inside-negative or an inside-positive membrane potential.
Determination The “cell fate” in embryogenesis that comits the cell to a specific developmental pathway.
Development The overall events that involve growth, differentiation, and organization in which the fertilized egg gives rise to an adult plant, animal, or human, including formation, growth, polarization, and movements of individual cell types, tissues, and organs.
Differentiation The process that typically produces changes in gene expression, by which, a precursor cell becomes a distinct specialized cell form.
Diploid Referring to an organism or cell having two full sets of homologous chromosomes and thus two copies (alleles) of each gene or genetic locus. Somatic cells contain the diploid number of chromosomes (2n) characteristic of the species.
Disaccharide A small carbohydrate (sugar) made up of two monosaccharides covalently joined by a glycosidic bond.
Disulfide bond (-s-s-) A common covalent linkage between the sulfur atoms on two cysteine residues in different polypeptides or in different locations of the same polypeptide.
DNA (deoxyribonucleic acid) Long linear polymer, composed of genetic information.
DNA cloning Recombinant DNA technique in which specific cDNAs or fragments of genomic DNA are inserted into a cloning vector (virus), which is then incorporated into cultured host cells and maintained during the growth of the host cells (also referred to as gene cloning).
DNA library Collection of cloned DNA molecules consisting of fragments of the entire genome (genomic library) or of DNA copies of all the mRNAs produced by a cell type (cDNA library) inserted into a suitable cloning vector.
DNA polymerase An enzyme that copies one strand of DNA (the template strand) to make the complementary strand, forming a new double-stranded DNA molecule. All DNA polymerases add deoxyribonucleotides one at a time in the 5’-> 3’ direction to the 3’ end of a short preexisting primer strand of DNA or RNA.
Domain Distinct regions of a protein’s three-dimensional structure. A functional domain exhibits a particular activity characteristic of the protein; a structural domain is =40 or more amino acids in length, arranged in a specific secondary or tertiary structure; a topological domain has a distinctive spatial relationship to the rest of the protein.
Dominant In genetics, the term refers to that allele of a gene expressed in the phenotype of a heterozygote; the nonexpressed allele is recessive; dominant also refers to the phenotype associated with a dominant allele. Mutations that produce dominant alles generally produce a gain of function.
Double helix (DNA) The most common three-dimensional structure for cellular DNA in which the two polynucleotide strands are antiparallel and wound around each other with complementary bases hydrogen-bonded.
Dyneins A class of motor proteins that employ the energy released by ATP hydrolysis to move toward the negative end of microtubules. Dyneins transport vesicles and organelles, are responsible for the movement of cilia and flagella, and are instrumental in chromosome movement during mitosis.
E
Ectoderm The outermost of the three primary cell layers of the animal embryo. It gives rise to the epidermal tissues, the nervous system, and external sense organs.
Electric potential The energy associated with the separation of positive and negative charges. An electric potential is maintained across the plasma membrane of almost all cells.
Electrochemical gradient The driving force that determines the energetically favorable direction of transport of an ion (or charged molecule) across a membrane. It represents the combined influence of the ion’s concentration gradient across the membrane and the membrane potential.
Electron carrier Any molecule or atom that accepts electrons from donor molecules and transfers them to acceptor molecules in coupled oxidation and reduction reactions.
Electron transport Flow of electrons through a series of electron carriers from reduced electron donors (i.e., NADH) to O2 in the inner mitochondrial membranes, or from H2O to NADP+ in the thylakoid membrane of plant chloroplasts.
Embryogenesis Early development of an individual from a fertilized egg (zygote).
Embryonic stem (ES) cells A line of cultured cells derived from very early embryos that can differentiate into a wide range of cell types either in vitro or in vivo following reinsertion into a host embryo.
Endocrine A signaling mechanism in which target cells bind and respond to a hormone released into the blood stream by distant specialized secretory cells usually present in the form of a gland (i.e., pituitary, thyroid, ovary, testes, adrenal, etc.).
Endocytosis General term for the uptake of extracellular material by the invagination of the plasma membrane (i.e., endocytosis, phagocytosis, pinocytosis, etc.).
Endoderm The innermost of the three primary cell layers of the animal embryo which gives rise to the gut and most of the respiratory tract.
Endoplasmic reticulum (ER) Network of interconnected membranous located in the cytoplasm of eukaryotic cells that are contiguous with the outer nuclear envelope. The rough ER, which is associated with ribosomes, is involved in the synthesis and processing of secreted and membrane proteins. The smooth ER, characterized by the lack of ribosomes, participates in lipid synthesis.
Endosome One of two forms of membrane bounded compartments. Early endosomes (endocytic vesicles) which bud off from the plasma membrane during receptor-mediated endocytosis. Late endosomes, which have an acidic internal pH and function in sorting of proteins to lysosomes.
Endosymbiont Bacterium that reside inside a eukaryotic cell in a mutually beneficial relationship. According to the endosymbiont theory, both mitochondria and chloroplasts evolved from endosymbionts.
Enhancer A regulatory sequence in eukaryotic DNA that may be located at a great distance from the gene it controls or even within the coding sequence. Binding of specific proteins to an enhancer modulates the rate of transcription of the associated gene.
Entropy (S) A measure of the degree of disorder or randomness in a biological system – the higher the level of entropy, the higher the level of disorder.
Enzyme A protein that does work by catalyzing a specific chemical reaction involving a specific substrate or a small collection of related substrates.
Epigenetic A term that refers to a process that affects the expression of specific genes and is inherited by daughter cells; however, the process does not include a change in DNA sequence.
Epithelium Sheet-like layer, covering, composed of one or more layers of tightly adhering cells, on the external and internal body surfaces.
Erythropoietin (Epo) A cytokine that initiates the production of red blood cells by inducing the proliferation and differentiation of erythroid progenitor cells in the bone marrow.
Eukaryotes Class of organisms (eukarya) that are composed of one or more cells containing a membrane-enclosed nucleus, and organelles, that constitute one of the three distinct evolutionary lineages of modern-day organisms. This includes all organisms except viruses and prokaryotes.
Exon Segment of a eukaryotic gene that reaches the cytoplasm as part of a mature mRNA, rRNA, or tRNA molecule.
Extracellular matrix (ECM) A complex interdigitating mesh of proteins and polysaccharides secreted by cells into the spaces in between each other. It provides structural support in tissues and organs and can directly affect the development and biochemical functions of cells.
F
Facilitated (diffusion) transport Protein-aided transport of an ion or small molecule across a cell membrane down its concentration gradient at a rate greater than that which can be obtained by simple diffusion.
FAD (flavin adenine dinucleotide) A small organic molecule that functions as an electron carrier by accepting two electrons from a donor molecule and two H+ from the solution.
Fatty acid Any of a series of long hydrocarbon chain that has a carboxyl group at one end. They are employed as a major source of energy during metabolism and a precursor for synthesis of phospholipids, triglycerides, and cholesterol esters.
Fibroblast A common type of connective tissue cell that is involved with the production of collagen and other connective tissue elements of the extracellular matrix. They can act as a stem cell and they can migrate and proliferate to facilitate wound healing (this feature is taken advantage of with cell cultures).
Flagellum Long locomotory structure (most often one per cell) protruding from the surface of some eukaryotic cells (e.g., sperm, bacteria, etc.) that is employed with a whip-like waving that propels the cell through a fluid medium. Bacterial flagellum tend to be smaller and much simpler structures than those of sperm.
Flavin adenine dinucleotide FAD
G
Gamete Specialized haploid cell (in animals and humans: sperm and ova) produced by meiosis of precursor germ cells. In sexual reproduction systems, the fertilization of an ova by a sperm initiates the development of a new organism.
Gastrulation Process in early animal embryos in which cells of the blastocyst invaginate, producing the three germ layers: ectoderm, mesoderm, and endoderm.
Gene Physical and functional unit of heredity, which carries information from one generation to the next. In molecular terms the “gene” is the entire DNA sequence —including exons, introns, and transcription-control regions— necessary for the production of a functional polypeptide or RNA.
Gene expression General process by which the information encoded in a gene is converted into an observable phenotype such as the production of proteins.
Genetic code The set of standards by which nucleotide triplets (codons) in DNA or RNA specify amino acid and amino acid sequences in proteins.
Genetic mapping Determination of the locations and relative positions of genes on a chromosome.
Genetic markers Alleles associated with an easily detectable phenotype that are used experimentally or for diagnostics to identify or select for a linked gene, a chromosome, a cell, or an individual.
Genome Total genetic information carried by a cell or organism.
Genomic imprinting Process that occurs during development of gametes involving chromatin modifications so that only certain genes can subsequently be expressed. Because different genes are imprinted in male and female gametes, the phenotype expression of certain genes is determined by whether a specific allele is passed on through the female or male parent.
Genomics Comparative analysis of the complete genomic sequences from different organisms and determination of global patterns of gene expression. It is used to determine evolutionary relationships among species and to predict the number and general types of RNAs produced by an organism.
Genotype The complete genetic makeup of an individual cell or organism with emphasis on the specific alleles.
Germ cell Any cell that participates “sexually” to the generation of offspring.
Germ layers Three primary cell layers (i.e., ectoderm, endoderm, and mesoderm) that are formed during the gastrulation of embryos that produce specific tissues and organs.
Germ line The genetic material transmitted from one generation to the next through the gametes.
Glial cells Support tissue cells in the central nervous system. They do not transmit electrical or chemical messages. There are four forms of glia cells: (1) Schwann cells; (2) oligodendrocytes (both of which produce the insulating myelin sheaths; (3) astrocytes participate in synapse formation; (4) microglia which produce trophic factors that participate in the central nervous systems immune response.
Glucagon A peptide hormone produced in the cells of the Islets of Langerhans that initiates the conversion of glycogen to glucose by the liver and works with insulin to maintain healthy blood sugar levels.
Glucose A six-carbon monosaccharide (sugar) that is the universal fuel for most cells. Glucose energy is stored as long polymer chain in plants (starch) and animals (glycogen).
Glycogen Also known as “animal starch” is stored in the liver and skeletal muscles and is comprised of glucose units forming a long branched polysaccharide.
Glycolysis Metabolic process in which sugars are broken down anaerobically to lactate or pyruvate which results in the production of ATP.
Glycoprotein Any protein that is covalently linked to one or more oligosaccharide chains – most secreted proteins and most membrane proteins are glycoproteins.
Golgi complex (Golgi apparatus) Stacks of flattened , interconnected membrane wrapped compartments (cisternae) in eukaryotic cells that act as a gate keeper to process and sort proteins and lipids moving to other locations.
Growth factor An extracellular polypeptide molecule that binds to cell surface receptors that initiate cell proliferation via a signaling pathway.
H
Haploid Referring to a cell or an organism, that has only one member of each pair of homologous chromosomes and thus have only one copy (allele) of each gene pair. Typically gametes (e.g., ova and sperm) and bacteria are haploid.
Hedgehog (Hh) A group of secreted signaling proteins that are regulators of the development of most tissues and organs in complex species including humans. In the genetic theory of disease transmission mutations in Hh signal-transduction segments are blamed for human cancer and birth defects.
Helicase Any enzyme that works along a DNA duplex employing the energy released by ATP hydrolysis to unwind the two strands required for DNA replication; activity of specific initiation factors that unwind the secondary structures in mRNA during translation.
Heterochromatin Zones of chromatin that remain condensed and transcriptionally inactive during interphase.
Heterozygous Referring to a diploid cell or organism having two different allels of a specific gene.
High-density lipoprotein (HDL) Thought to be the “good” form of cholesterol/protein complex.
Homeosis Transformation of one body part into another resulting from mutations in or misexpression (malnutrition) of certain developmentally critical genes.
Homologous chromosome One of two copies of each morphologic form of chromosome present in a diploid cell, also referred to as a homolog.
Homologs (homologues) Maternal and paternal copies of each morphologic type of chromosome present in a diploid cell.
Homozygous A diploid cell or organism having two identicle alleles of a particular gene.
Hormone An extracellular substance that circulates in the blood and initiates specific responses (endocrine signaling) in target cells distant from the gland or location of production.
Hox genes Group of developmentally important genes that encode homeodomain-containing transcription factors that help direct the body construction plan in animals and humans. Mutations (caused by malnutrition) in Hox genes produce homeosis.
Hyaluronan (hyaluronic acid) A large, highly hydrated glycosaminoglycan (GAG) that is a significant part of the extracellular body matrix (i.e., cartilage, tendons, ligaments, joint capsules, tendon sheaths, intracellular connective tissue, etc.), that produces stiffness and resilience and lubricating functions to a variety of connective tissue.
Hydrocarbon Any compound made up of carbon and hydrogen atoms.
Hydrophilic Substances that are attracted to and interact with water.
Hydrophobic Substances that are repelled by or fail to interact with water.
Hypertonic An external solution in which the solute concentration is high enough to pull water out of cells due to osmotic pressure (osmosis).
Hypotonic An external solution in which the solute concentration is low enough to cause water to be pulled into the cells due to osmotic forces (osmosis).
I
Immunity State of being resistant (immune) against the negative effects from exposure to pathogens, either in the form of innate nonspecific responses, that develop within moments to hours; or adaptive responses, which take several days or weeks to produce highly specific defenses.
Induction In embryogenesis, induction refers to a change in the developmental fate of one cell or tissue produced by signals or direct contact from a different cell or tissue; or in metabolism, an increase in the synthesis of an enzyme or series of enzymes mediated by a specific molecule or inducer.
Inflammation Localized response (such as redness, swelling, heat, and pain) to an injury or infection that leads to the activation of immune-system cells and their recruitment to the affected site
Inositol 1,4,5-trisphosphate (IP3) Intracellular second messenger produced by cleavage of the membrane lipid phosphatidyl-inositol 4,5-bisphosphate in response to the stimulation of specific cell-surface receptors.
Insulin A protein hormone produced in the Beta cells of the pancreatic islets that facilitates the uptake of glucose into muscle and fat cells. Insulin acts with glucagon, chromium and vanadium to regulate blood sugar levels; insulin also acts as a growth factor for a variety of cells.
In vitro A reaction or test that takes place in an isolated cell culture rather than in an intact living organism.
In vivo A reaction or test that takes place in an intact cell, tissue, organ, or intact organism.
Isotonic A solution is that has a solute concentration that does not cause any net movement of water from inside the cell out or from outside the cell in.
K
Karyotype Number, sizes, and shapes of the entire set of metaphase chromosomes of a eukaryotic cell.
Keratins A species of filament proteins found in epithelial cells.
Kinase A form of enzyme that transfers the terminal phosphate group from ATP to a substrate.
Kinetic energy The energy of movement, including the movement of molecules and whole organisms.
Kinetochore A multilayer protein structure located at or near the centromere of each mitotic chromosome from which microtubules extend toward the spindle poles of the cell. It is involved in an active role in the movement of chromosomes toward the poles during anaphase of cell division.
L
Lagging strand (Okazaki fragments) One of two daughter DNA strands formed at a replication fork as short, discontinuous segments.
Lamins A group of intermediate filament proteins that form a fibrous network (i.e., nuclear lamina) on the inner surface of the nuclear envelope.
Lectin Any protein that binds tightly to specific sugars. Lectins support the proper folding of certain glycoproteins in the endoplasmic reticulum.
Ligand Any molecule, except for an enzyme substrate, that binds tightly and specifically to a protein macromolecule.
Linkage In genetics, linkage is the tendency of two separate loci on the same chromosome to be inherited together. The closer the two loci are, the lower the frequency of recombination between them and the tighter their linkage.
Lipid (fats) Any organic molecule that is insoluble in water, however, is remarkably soluble in nonpolar organic solvents (e.g., ether, chloroform, etc.).
Lipid raft Microdomain in the plasma (cell) membrane that is rich in cholesterol, sphingomyelin, and specific proteins.
Lipoprotein Any large, water-soluble protein-lipid complex that performs in mass transfer of lipids throughout the body.
Locus (pl. loci) In genetics, a specific site of a gene on a chromosome. All the alleles of a particular gene occupy the same locus.
Low-density lipoprotein (LDL) A class of lipoprotein, containing apolipoprotein B-100, that is a primary transporter of cholesterol in the form of cholesteryl esters between tissues, particularly the liver. It is thought to be the “bad” cholesterol.
Lumen The space within a tubular structure (i.e., blood vessel, gastrointestinal tract, or the interior of a membrane enclosed structure within a cell, etc.).
Lymphocytes Two species of white blood cells (WBC) that can identify foreign molecules or antigens and trigger an immune response. B cells (B lymphocytes which are activated by the appendex) which trigger the production of antibodies and T cells (T lymphocytes which are activated by the thymus) which destroy virus and bacteria-infected cells, foreign cells, and cancer cells.
Lysis Destruction of a cell by the rupture or dissolving of the plasma membrane and release of its contents (e.g., hemolytic anemia, etc.).
Lysosome Small organelle that has an internal pH of 4 – 5, contains hydrolytic enzymes, and functions in the degradation of materials internalized by endocytosis and of cellular components in autophagy.
M
Macromolecule Any large, commonly a polymeric molecule (i.e., protein, nucleic acid, polysaccharide, etc.) with a molecular mass greater than a few thousand daltons.
Macrophages A species of phagocytic leukocytes that have the ability to detect broad patterns of pathogen markers via Toll-like receptors. They function as “professional” antigen-presenting cells and are a major source of cytokines.
Malignant A tumor or tumor cells that can invade adjacent normal tissue and travel via the blood stream to distant locations (metastasis).
Mediator A very large multiprotein complex that forms a molecular bridge between transcriptional activators bound to an enhancer and to RNA polymerase II bound at a promoter. This functions as a coactivator in stimulating transcription.
Meiosis In eukaryotes, a special type of cell division that occurs during the maturation phase of germ cells. The process is made up of two successive nuclear and cellular divisions with only one round of DNA replication, and this process produces four genetically nonequivalent haploid cells (gametes) from an initial diploid cell.
Membrane potential Electric potential difference, expressed in volts, across a membrane due to the slight excess of positive ions (cations) on one side and negative ions (anions) of the other.
Meristem Organized cluster of undifferentiated, dividing cells that are maintained at the tips of growing shoots and roots in plants. All of the adult structures of the plant arise from meristems.
Mesenchyme Immature embryonic connective tissue, composed of loosely organized and loosely attached cells, derived from either the mesoderm or ectoderm in animals.
Mesoderm The middle layer of the three primary cell layers of the animal embryo, lying between the ectoderm (outer layer) and the endoderm (inner layer). This layer of cells gives rise to the notochord, connective tissue, muscle, bone marrow, blood, etc.
Metaphase A stage in the process of mitosis at which condensed chromosomes are aligned equidistant between the poles of the mitotic spindle, but have not yet started to migrate toward the spindle poles.
Metastasis The spread of cancer cells from their original site of origin and resulting areas of secondary growth in distant locations.
Micelle A water-soluble spherical aggregate of phospholipids or other amphipathic molecules that form spontaneously in aqueous solution.
Microfilament Cytoskeletal fiber (=7 nm in diameter) that is formed by polymerization of monomeric globular (G) actin (i.e., actin filament). Microfilaments have an important role in muscle contraction, cytokinesis, cell movement, etc.
Microtubule Cytoplasmic fiber (=25 nm in diameter) that is formed by polymerization of alpha, beta tubulin monomers and exhibits structural and functional polarity. Microtubules are significant components of cilia, flagella, the mitotic spindle and other cellular structures.
Microvillus (pl. microvilli) Small, membrane-covered projections on the surface of an animal cell containing a core of actin filaments. Numerous microvilli are found on the absorptive mucosal surface of intestinal epithelial cells, significantly increasing the surface area for transport of nutrients into the enteric vascular system.
Mitochondrion (pl. mitochondria) Large intracellular organelle that is surrounded by two phospholipid bilayer membranes, contains DNA, and performs oxidative phosphorylation, by which it produces the majority of ATP in eukaryotic cells.
Mitogen Any extracellular molecule (e.g., growth factor, etc.) that induces cell proliferation.
Mitosis In eukaryotic cells, it is the process by which the nucleus divides, producing two genetically equivalent daughter nuclei with the diploid number of chromosomes.
Mitotic spindle (mitotic apparatus) A temporary specialized structure, occurs in eukaryotic cells during mitosis, that captures the chromosomes and then pushes and pulls them to opposite sides of the dividing cell.
Molecular markers (DNA-based) DNA sequences that vary among individuals (DNA polymorphisms) of the same species and are useful in genetic linkage studies.
Monoclonal antibody Antibody produced by the progeny of a single B cell and therefore a homogeneous protein that recognizes a single antigen (epitope).
Monomer Any small molecule that can be linked chemically with others of the same type to form a polymer (e.g., amino acids, nucleotides, monosaccharides, etc.).
Monosaccharide Any simple sugar with the formula (CH2O)n where n = 3 – 7.
Morphogen A signaling molecule that directs different cell fates during development.
Mutagen A chemical or physical agent that induces mutations (such as radiation, DDT, etc.)
Mutation In genetics, a permanent, heritable change in the nucleotide sequence of a chromosome, usually in a single gene, and produces an alteration in the function or structure of the gene product.
Myelin sheath Stacked specialized cell membranes that forms an insulating layer around vertebrate axons and enhances the speed of impulse conduction.
Myosins A class of motor proteins that have actin-stimulated ATPase activity. Myosins move along actin microfilaments during muscle contraction and cytokinesis. Additionally they mediate vesicle translocation.
N
NAD+ (nicotinamide adenine dinucleotide) A small organic molecule that functions as an electron carrier by accepting two electrons from a donor molecule and one H+ from the solution.
Natural killer (NK) cells Components of the innate immune system that nonspecifically detects and kills virus-infected cells and cancer cells.
Necrosis Cell death resulting from nutritional deficiency (e.g., liver necrosis/selenium deficiency, etc.), tissue damage, or other pathology, commonly marked by swelling and the bursting of cells with the resultant release of their contents.
Neuron (nerve cells) Any of the impulse-conducting cells of the nervous system. A typical neuron contains a cell body, multiple short-branched processes (dendrites), and one long process (axon) that transmit impulses to adjacent neurons or other tissues (such as muscle, glands, etc.).
Neurotransmitter extracellular signaling molecule that is released by the presynaptic neuron at a chemical synapse and relays the signal to the postsynaptic cell.
Neurulation Formation of the neural tube by infolding of the neural plate, the portion of the ectoderm that develops into neural structures, in vertebrate embryos.
Neutrophils Phagocytic leukocytes that are attracted to sites of tissue damage and migrate into the tissue. Once activated, neutrophils secrete various chemokines, cytokines, bacteria-destroying enzymes (e.g., lysozyme), and other products that contribute to inflammation and help clear invading pathogens.
Nuclear body A spherical, functionally specialized region in the nucleus – it contains specific proteins and RNAs; many function in the assembly of ribonucleoprotein (RNP) complexes. The most common form of this structure is the nucleolus.
Nucleic acid A polymer of nucleotides linked by phosphodiester bonds. DNA and RNA are the primary nucleic acids in cells.
Nucleolus A large structure in the nucleus of eukaryotic cells where rRNA synthesis and processing occurs and ribosome sub-units are assembled.
Nucleoside A small molecule composed of a purine orpyrimidine base linked to a pentose (either ribose or deoxyribose).
Nucleotide A nucleoside with one or more phosphate groups linked via an ester bond to the sugar moiety, typically to the 5’ carbon atom. DNA and RNA are polymers of nucleotides containing deoxyribose and ribose, respectively.
Nucleus Large membrane bounded organelle in eukaryotic cells that contains DNA organized into chromosomes; synthesis and processing of RNA and ribosome assembly occur in the nucleus.
O
Okazaki fragments Short (< 1000 bases), single-stranded DNA fragments that are formed during the synthesis of the lagging strand in DNA replication and are rapidly joined by DNA ligase to form a continuous DNA strand.
Oligopeptide A small to medium-sized linear polymer composed of amino acids connected by peptide bonds.
Oncogene A gene in which the product of their activity is either in transforming cells in culture or in inducing cancer in animals and humans.
Organelle Any membrane-limited subcellular structure found in eukaryotic cells.
Organ of Corti Acoustic sensory structure housed within the cochlea of the inner ear and composed of hair cells that transduce sound-generated mechanical movement into electrical impulses.
Osmosis Net movement of water across a semipermeable membrane (permeable to water but not solute) from a solution of lesser to one of the greater solute concentration.
Oxidation Loss of electrons from an atom or molecule as occurs when a hydrogen atom is removed from a molecule or oxygen is added—the opposite of reduction.
Oxidation potential The voltage change when an atom or molecule loses an electron and the measure of the tendency of a molecule to loose an electron. For a given oxidation reaction, the oxidation potential has the same magnitude but opposite sign as the reduction potential for the reverse reduction reaction.
Oxidative phosphorylation The phosphorylation of ADP to form ATP driven by the transfer of electrons to oxygen (O2) in bacteria and mitochondria. Involves generation of a proton-motive force during electron transport and its consequent use to generate ATP synthesis.
P
Paracrine A signaling mechanism in which a target cell responds to a signaling molecule (i.e., growth factor, neuro-transmitter, etc.) that is produced by a nearby cell(s) and reaches the target by diffusion.
Pattern formation Process of organizing the cells, organs, and tissues of a developing embryo into well-ordered spatial patterns, like the bones of a hand or the color pattern on a butterfly wing.
Pentose A five-carbon monosaccharide. The pentoses ribose and deoxyribose are present in RNA and DNA, respectively.
Peptide A small linear polymer composed of amino acids connected by peptide bonds. The terms peptide and oligopeptide are often used interchangeably.
Peptide bond The covalent amide linkage between amino acids formed between the amino group of one amino acid and the carboxyl group of another with the net release of a water molecule.
pH A measurement of the acidity or alkalinity of a solution defined as the negative logarithm of the hydrogen ion concentration in moles per liter. Neutrality is equivalent to a pH of 7. Values below 7 are considered acidic and values above 7 are considered alkaline.
Phagocyte Any cell that can ingest and destroy pathogens and other particulate antigens. The primary phagocytes are neutrophils, macrophages, and dendritic cells.
Phagocytosis Process during which large particles (i.e., bacteria, yeast, cancer cells, etc.) are consumed and ingested by phagocytic eukaryotic cells that use a process that employs significant remodeling of the actin cytoskeleton.
Phenotype The detectable physical and physiological characteristics of a cell or organism determined by its genotype. In genetic terms the phenotype is a specific trait associated with a particular allele.
Pheromone A signaling molecule released by an individual that can alter the behavior or gene expression of other individuals of the same species (e.g., sexual attraction, etc.).
Phospholipids A major class of lipids present in biomembranes, including phosphoglycerides and sphingolipids.
Photosynthesis Series of reactions occurring in some bacteria and in plant chloroplasts in which light energy is used to synthesize carbohydrates from CO2.
Plasma membrane The membrane surrounding a cell that seperates the cell from its external environment. It consists of a phospholipid bilayer and associated membrane lipids and proteins.
Plasmid Small round extrachromosomal DNA molecule capable of autonomous replication in a cell.
Polymer Any large molecule made up of identical multiple or similar units (monomers) linked by covalent bonds.
Polyphenols High dietary intake of polyphenols is associated with a 30% reduction of mortality rates in older adults. The most important food sources of polyphenols include fruit, vegetables, green tea, black tea, red wine, coffee, chocolate, olives; herbs, spices, nuts, and algae that can supply certain polyphenols. Some polyphenols are specific to particular foods (flavanones in citrus fruit, isoflavones in soya, phloridzin in apples); whereas others, such as quercetin, are found in all plant products such as fruit, vegetables, cereals, legumes, tea, and wine.
Polypeptide Linear polymer of amino acids connected by peptide bonds and usually made up of 20 or more amino acids.
Polyunsaturated Referring to a long chain fatty acid in which there are two or more of the carbon-carbon bonds are double or triple bonds.
Prion Thought to be an infectious form of protein crystal that increases in number by converting related proteins into more prions; falsely thought to be the causative organism of Bovine Spongioform Encephalitis (BSE, Mad Cow Disease) and the human form of CJD.
Proteome The entire collection of proteins produced by a cell.
Proteomics A systematic study of the amounts, modifications, interactions, localization, and functions of all or subsets of proteins at the whole-organism, tissue, cellular, and subcellular levels.
Purines A class of nitrogenous compounds containing two fused heterocyclic rings. Two purines, adenine (A) and guanine (G), are base components of nucleotides found in DNA and RNA.
Pyrimidines A class of nitrogenous compounds containing one heterocyclic ring. Two pyrimidines, cytosine (C) and thymine (T), are base components of nucleotides found in DNA; in RNA, uracil (U) replaces thymine.
Q
Quaternary structure The number and relative positions of the polypeptide chains in multimeric (multisubunit) proteins.
R
Receptor Any protein that specifically binds another molecule to mediate cell-cell signaling, adhesion, endocytosis, or other cellular process. Commonly refers to a protein located in the plasma membrane, cytosol, or nucleus that binds a specific extracellular molecule (ligand), which frequently produces a conformational change in the receptor, resulting in a cellular response.
Recessive In genetic terms, recessive refers to that allele of a gene that is not expressed in the phenotype when the dominant allele is present; also can refer to the phenotype of an individual (homozygote) carrying two recessive alleles. Mutations that produce recessive alleles generally result in a loss of the gene’s primary function.
Recombinant DNA Any DNA molecule formed in vitro by joining DNA fragments from different sources.
Redox reaction An oxidation-reduction reaction in which one or more electrons are transferred from one reactant to another.
Reduction Gain of electrons by an atom or molecule as occurs when a hydrogen atom is added to a molecule or oxygen is removed. This is the opposite of oxidation.
Reduction potential (E) The voltage change when an atom or molecule gains an electron and a measure of the tendency of a molecule to gain an electron. For a given reduction reaction, E has the same magnitude but opposite sign as the oxidation potential for the reverse (oxidation) reaction.
Ribosome A large complex comprising several different rRNA molecules and more than 50 proteins, organized into a large subunit and small subunit. The ribosome is responsible for protein synthesis (translation).
RNA (ribonucleic acid) Linear, single-stranded polymer, composed of ribose nucleotides, mRNA, rRNA, and tRNA play different roles in protein synthesis. A variety of small RNAs play roles in controlling the stability and translation of mRNAs, and in controlling chromatin structure and transcription.
S
Sarcomere Repeating structural unit of striated (skeletal) muscle composed of organized, overlapping thin (actin) filaments and thick (myosin) filaments and extending from one Z disk to an adjacent one. The sarcomere shortens during contraction.
Sarcoplasmic reticulum Network of membranes in cytoplasm of a muscle cell that sequesters Ca2+ ions; release of stored Ca2+ induced by muscle stimulation initiates contraction.
Segregation The process that distributes an equal complement of chromosomes to daughter cells during mitosis and meiosis.
Somatic cell Any plant or animal cell other than a germ cell.
Starch A very long, branched polysaccharide, composed exclusively of glucose units, that is the primary storage carbohydrate in plant cells.
Stem cell A self-renewing cell that can divide symmetrically to give rise to two daughter cells whose developmental potential is identical to the parental stem cell or asymmetrically to generate daughter cells with different developmental potentials.
Steroids A group of four-ring hydrocarbons including cholesterol and related compounds. Many important hormones (i.e., testosterone, estrogen, progesterone, adrenal hormones) are steroid hormones. Sterols are steroids containing one or more hydroxyl groups.
Synapse Specialized zone between an axon terminal of a neuron and an adjacent neuron or excitable cell (such as a muscle cell) across which impulses are transmitted. At a chemical synapse, the impulse is conducted by a neurotransmitter; at an electric synapse, impulse transmission occurs via gap junctions connecting the pre- and postsynaptic cells.
T
T cell A lymphocyte that matures in the thymus and expresses antigen-specific receptors that bind antigenic peptides complexed to MHC molecules. There are two large classes: cytotoxic T cells (CDS surface marker, class I MHC restricted, kill virus-infected and cancer cells), and helper T cells (CD4 marker, class II MHC restricted, produce cytokines, required for activation of B cells.
Telomere Region on each end of a eukaryotic chromosome containing multiple tandem repeats of a telomere (TEL) sequence. Telomeres are required for proper chromosome segregation and are replicated by a special process that prevents shortening of chromosomes during DNA replication. Maintenance of telomere length after each cell division is thought to extend the life of the organism.
Telophase Final mitotic stage during which the nuclear envelope re-forms around the two sets of separated chromosomes, the chromosomes decondense, and division of the cytoplasm (cytokinesis) is completed.
Thylakoid A flattened membrane sac inside the chloroplast which converts light energy to chemical energy.
Trace element A element essential for the life of vertebrates that are required in extremely small doses.
Translation The ribosome-mediated assembly of a polypeptide whose amino acid sequence is specified by the nucleotide sequence in an mRNA.
Triglyceride Major molecular form in which fatty acids are stored and transported in animals – it is made up of three fatty acid chains esterified to a glycerol molecule.
Trophic factor A large variety of signaling proteins required for the survival of cells in multicellular organisms. In the absence of such signals cells will commit suicide by apoptosis.
Tumor A mass of cells, typically originating from a single cell type – may be benign or malignant.
U
Ubiquitin A small protein that can be covalently linked to other intracellular proteins, thus tagging the proteins for degradation by the proteasome, sorting to the lysosome, or alteration in the function of the target protein.
Uncoupler Any natural substance (e.g., the protein thermogenin) or chemical (e.g., 2,4-dinitrophenol) that dissipates the proton-motive force across the inner mitochondrial membrane or thylakoid membrane of chloroplasts which inhibits ATP synthesis.
Uniport A form of transport in which a membrane protein (uniporter) facilitates the movement of a small molecule across a membrane down its concentration gradient by facilitated transport. The glucose transporters (GLUT proteins) are iconic examples of uniporters.
Unsaturated Referring to the state of a fatty acid in which at least one of the carbon-carbon bonds is a double or triple bond.
Upstream In genetics upstream refers to the direction opposite to that in which RNA polymerase moves during transcription; the events that can occur earlier in a cascade of signaling pathway steps.
Upstream activating sequence (UAS) Any protein-binding regulatory sequence in DNA of yeast and other simple eukaryotes that is necessary for maximal gene expression and is equivalent to an enhancer or promoter-proximal element in higher eukaryotes.
V
Vaccine A preparation derived from a pathogen and designed to initiate an immune response to produce immunity to resist a future exposure by the virulent form of the identical pathogen.
Vector A tool in cell biology, an autonomously replicating genetic element employed to carry a cDNA or fragment of genomic DNA into a host cell for the purpose of gene cloning. Commonly used vectors are bacterial plasmids and modified viral bacteriophage genomes.
Viroid A plant pathogen composed of molecules of naked RNA only several hundred nucleotides long.
Virus A small intracellular pathogen, made up of nucleic acid (RNA or DNA) enclosed in a protein coat, that can replicate only in a susceptible host cell.
Vitamin An essential organic molecule required in the diet of all animals and humans in very small levels; vitamins serve primarily as coenzymes or parts of coenzymes and cofactors to facilitate the physiological requirements of life.
W
Western blotting (immunoblotting) Technique in which proteins separated by electrophoresis are attached to a nitrocellulose or other membrane, and specific proteins then are detected by use of labeled antibodies.
Wild type A normal, nonmutant form of a gene, protein, cell, or organism.
X
X-ray crystallography Commonly used technique for establishing the three-dimensional structure of macromolecules (especially proteins and nucleic acids) by passing x-rays through a crystal of the purified molecules and analyzing the diffraction pattern of the discrete dots that are produced.
Z
Zinc finger Several related DNA-binding structural motifs composed of secondary structures folded around a zinc ion present in a variety of eukaryotic transcription factors.
Zygote A fertilized egg; a diploid cell resulting from the fusion of a male and female gamete.