BIO - TERMS - FREQUENCY > 4 Flashcards
acid
A molecular compound that is able to donate an H+ ion (proton donor) when dissolved in water, forming hydronium ions (H3O+) and lowering the pH. // A substance that dissociates into one or more hydrogen ions (H+) and one or more negative ions. // Substance that releases a hydrogen ion when added to a solution.
actin
Contractile protein forming the major part of the thin filaments in a sarcomere. // A protein that makes up the thin filaments of muscle; also an important component of the cytoskeleton of many eukaryotic cells. // A cytoskeletal protein in all cells and the major thin fi lament protein in a skeletal muscle fiber; causes muscle contraction by specific chemical interactions with myosin. // A globular protein that polymerizes into microfilaments. // Thin contractile protein of muscle tissue.
activation energy (DG‡)
An energy barrier in a chemical reaction that must be overcome for the reactants to be converted into products. (15.5) active site The specific area of an enzyme in which catalysis occurs. // The minimum collision energy required for a chemical reaction to occur. // The difference in energy between ground state and transition state in a reaction. The amount of activation energy determines the rate at which the reaction proceeds. Most organic reactions have activation energies of 40–100 kJ/mol. // The extra energy that must be acquired by atoms or molecules in addition to their ground-state energy in order to reach the transition state required for them to undergo a particular chemical reaction. // The amount of energy (in joules) required to convert all the molecules in 1 mol of a reacting substance from the ground state to the transition state.
active site
The region of an enzyme surface that binds the substrate molecule and catalytically transforms it; also known as the catalytic site. // A region on an enzyme that interacts with the substrate. // Region of an enzyme surface to which a substrate molecule binds in order to undergo a catalyzed reaction. // The place on the enzyme protein to which the substrate binds and where catalysis takes place. // Region of an enzyme where substrate binds. // The pocket in an enzyme where a substrate is bound and undergoes reaction.
adenosine triphosphate (ATP)
A high-energy phosphate compound that allows for the release of energy when its phosphate bounds are broken. // An important intracellular energy source. // The “energetic currency” of the cell. // The molecule that is the cell’s energy source. The hydrolysis of ATP to produce adenosine diphosphate (ADP) releases energy that fuels most of the biochemical reactions of the neuron. ADP is converted back to ATP in the mitochondria. // Stores and releases chemical energy in a cell; composed of adenine, ribose, and three phosphate groups.
amino acid
An organic compound that contains a carbon atom, called the a-carbon, bonded to four different groups: an amine group, an R group, a carboxylic acid group, and a hydrogen atom. // Organic molecule containing both an amino group and a carboxyl group. Those that serve as building blocks of proteins are alpha amino acids, having both the amino and carboxyl groups linked to the same carbon atom. (NH2CHRCOOH) // A chemical building block of protein molecules, containing a central carbon atom, an amino group, a carboxyl group, and a variable R group. // An organic acid containing an amino group and a carboxyl group. In alpha-amino acids the amino and carboxyl groups are attached to the same carbon atom called the alpha-carbon. // Any one of a class of organic compounds containing an amino (NH2) group and a carboxyl (COOH) group. Amino acids are the building blocks of proteins. Alanine, proline, threonine, histidine, lysine, glutamine, phenylalanine, tryptophan, valine, arginine, tyrosine, and leucine are among the common amino acids. // Organic molecule used to build proteins; contains both an amine group and carboxyl group. // -Amino–substituted carboxylic acids, the building blocks of proteins.
amphipathic
Containing both polar and nonpolar domains. // Molecule that contains a hydrophobic region and a hydrophilic region. // Describes molecules that have a positively charged (or hydrophilic) region separated from a hydrophobic region. // Containing hydrophilic and hydrophobic portions in the same molecule. // Having both hydrophilic and hydrophobic portions.
anabolism
The phase of intermediary metabolism concerned with the energy-requiring biosynthesis of cell components from smaller precursors. // Formation of large, complex molecules from simple molecules. // The metabolic reactions by which larger molecules are built from simpler ones, with the consumption of energy. // All synthesis reactions in a living organism; the building of complex organic molecules from simpler ones. // The biosynthesis of organic molecules from nutritive precursors; also called anabolic metabolism. See also catabolism. // The group of metabolic pathways that build up larger molecules from smaller ones.
androgen
Male sex hormone; one type of androgen is testosterone. // A male hormone that controls sexual activity in vertebrate animals. // A male steroid sex hormone. // Male sex steroidal hormones, the most important of which is testosterone. // Male sex steroids derived from progestins by a side-chain cleavage reaction.
anion
Negatively charged ion; e.g., Cl−.
antagonist
Muscle (or hormone) that opposes or resists the action of another. // A compound that interferes with the physiological action of another substance (the agonist), usually at a hormone or neurotransmitter receptor. // An inhibitory ligand for a receptor. // A muscle that acts against another at the same joint. // Organisms that interfere with growth, survival and infection of pathogens.
antibody
A defense protein synthesized by the immune system of vertebrates. See also immunoglobulin. // Immunoglobulin that binds to a specific antigen; released by plasma cells (activated B-lymphocytes). // A protein produced by the body in response to an antigen, and capable of combining specifically with that antigen. // A protein that binds specifically to a particular substance—called its antigen. Each antibody molecule has a unique structure that enables it to bind specifically to its corresponding antigen, but all antibodies have the same overall structure and are known collectively as immunoglobulins. Antibodies are produced by differentiated B cells (plasma cells) in response to infection or immunization, and bind to and neutralize pathogens or prepare them for uptake and destruction by phagocytes. // Protein secreted by activated B cells in response to a pathogen or foreign molecule. Binds tightly to the pathogen or foreign molecule, inactivating it or marking it for destruction by phagocytosis or complement-induced lysis. // Substance in a tissue or fluid of the body that acts in antagonism to a foreign substance (antigen).
anticodon
A specific sequence of three nucleotides in a tRNA, complementary to a codon for an amino acid in an mRNA. // Three bases in a transfer RNA molecule that are complementary to the three bases of a specific codon in mes senger RNA. // Group of three nucleotide bases in a transfer RNA molecule; base pairs with a complementary codon on messenger RNA. // A sequence of three bases on tRNA that reads the codons on mRNA and brings the correct amino acids into position for protein synthesis. // Sequence of three nucleotides in a transfer RNA (tRNA) molecule that is complementary to a three-nucleotide codon in a messenger RNA (mRNA) molecule. // The base triplet of the tRNA that base pairs with the codon during protein synthesis. // The three nucleotides by which a tRNA recognizes an mRNA codon.
antigen
Substance that causes a state of sensitivity or responsiveness and reacts with antibodies or T-lymphocytes. // A molecule that can induce an adaptive immune response or that can bind to an antibody or T cell receptor. antigen-presenting cell Cell that displays foreign antigen complexed with an MHC protein on its surface for presentation to T lymphocytes. // Any molecule that can bind specifically to an antibody or generate peptide fragments that are recognized by a T-cell receptor. // A molecule capable of eliciting the synthesis of a specific antibody in vertebrates. // A substance, usually a protein, that is bound by an antibody or a T-cell receptor when introduced into a vertebrate organism. // Any substance that causes antibody formation; also called an immunogen. // Protein, DNA, lipid or polysaccharide that induces an immune response.
antigenic drift
The appearance of virus particles with a slightly altered surface protein (antigen) structure as a result of the accumulation of point mutations following passage and immune selection in the natural host. // The process by which influenza virus varies genetically in minor ways from year to year. Point mutations in viral genes cause small differences in the structure of the viral surface antigens. // A minor variation in the antigenic makeup of influenza viruses that occurs with time. // A major genetic change in influenza viruses causing changes in H and N antigens. // A major change in one or more surface proteins of a virus particle when genes encoding markedly diff erent surface proteins are acquired during infection; this process occurs when viruses with segmented genomes exchange segments, or when nonsegmented viral genomes recombine aft er coinfection. // A radical change in the surface antigens of influenza virus, caused by reassortment of their segmented genome with that of another influenza virus, often from an animal.
apoptosis
A form of cell death common in the immune system, in which the cell activates an internal death program. It is characterized by nuclear DNA degradation, nuclear degeneration and condensation, and the rapid phagocytosis of cell remains. Proliferating lymphocytes experience high rates of apoptosis during their development and during immune responses. // Form of programmed cell death, in which a “suicide” program is activated within an animal cell, leading to rapid cell death mediated by intracellular proteolytic enzymes called caspases. // Programmed cell death. // A mechanism of orderly, genetically programmed cell death. // A phenomenon in which eukaryotic cells die because of genetically programmed events within those cells. // Cell death following a sequence of tightly regulated reactions induced by external or internal stimuli that signal DNA damage or other forms of stress; characterized by chromosome degradation, nuclear degeneration and cell lysis; a natural process in development and the immune system, but also an intrinsic defense of cells to viral infection. Also called programmed cell death. ( Chapters 2 and 3) // Programmed cell-death leading to a progressive fragmentation of DNA and disintegration of cells without causing inflammation. // The natural programmed death of a cell; the residual fragments are disposed of by phagocytosis. // Programmed cell death in which a cell brings about its own death and lysis, in response to a signal from outside or programmed in its genes, by systematically degrading its own macromolecules.
autophagy
Catabolic lysosomal degradation of cellular proteins and other components. // Segregation and disposal of damaged organelles within a cell. autoregulation Intrinsic ability of an organ to regulate its activity. // A process leading to the lysosomal destruction of defective organelles and intracellular bacteria.// Digestion of cytoplasm and worn-out organelles by the cell’s own lysosomes. // The digestion and breakdown by a cell of its own organelles and proteins in lysosomes. It may be one route by which cytosolic proteins can be processed for presentation on MHC class II molecules. // A process in which cells are induced to degrade the bulk of their cellular contents for recycling within specialized membranebounded compartments called autophagolysosomes. ( Chapter 3) // The controlled degradation, in response to stress, of proteins and other cellular components taken into double-membrane vesicles (autophagosomes) that fuse with lysosomes, literally self-eating. (Chapter 14)
B lymphocyte (B cell)
One of the two types of antigen-specific lymphocytes responsible for adaptive immune responses, the other being the T cells. The function of B cells is to produce antibodies. B cells are divided into two classes. Conventional B cells have highly diverse antigen receptors and are generated in the bone marrow throughout life, emerging to populate the blood and lymphoid tissues. B-1 cells have much less diverse antigen receptors and form a population of self-renewing B cells in the peritoneal and pleural cavities. // A type of lymphocyte that produces membrane-bound immunoglobulin. // One of a class of blood cells (lymphocytes), responsible for the production of circulating antibodies. // An important class of cells that mature in bone marrow and are largely responsible for the antibodymediated or humoral immune response; they give rise to the antibody-producing plasma cells and some other cells of the immune system. // A type of lymphocyte; differentiates into antibody-secreting plasma cells and memory cells. // Immune cell that functions in antibodymediated immunity; matures into a plasma cell.
bacteriophage (phage)
A virus capable of replicating in a bacterial cell; also called phage. // “Phage”; bacteria-infecting virus. // A virus that attacks bacteria. Such viruses are called bacteriophages because they destroy their bacterial hosts. // A virus that infects bacterial cells. // Viruses that infect bacteria; derived from the Greek word phagein, meaning “to eat.” (Chapter 1)
bacterium (plural bacteria) (eubacterium)
One of the five kingdoms of living organisms; bacteria have a plasma membrane but no internal organelles or nucleus. // A vast kingdom of unicellular prokaryotic microorganisms, some species of which cause infectious diseases in humans and animals, while others make up most of the body’s commensal microbiota. Disease-causing bacteria may live in the extracellular spaces, or inside cells in vesicles or in the cytosol. // Domain of prokaryotic organisms, characterized by peptidoglycan cell walls; bacterium (singular) when referring to a single organism. // All bacteria consist of a single cell surrounded by a cell wall; DNA is circular; bacteria do not have internal membrane systems or a nucleus. // Member of the domain bacteria, one of the three main branches of the tree of life (archaea, bacteria, and eukaryotes). Bacteria and archaea both lack a distinct nuclear compartment, and together comprise the prokaryotes.
buffer
A solution containing significant amounts of both a weak acid and its conjugate base (or a weak base and its conjugate acid) that resists pH change by neutralizing added acid or added base. // A solution whose pH value is stabilized by the presence of ionizable groups. // A substance that tends to stabilize the pH of a solution. // Solution of weak acid or weak base that resists the pH change that would otherwise occur when small quantities of acid or base are added. // A system capable of resisting changes in pH, consisting of a conjugate acid-base pair in which the ratio of proton acceptor to proton donor is near unity. // Substance that minimizes a change in pH after an acid or base is added. // The difference between the percentage of 1RM necessary to go to failure with the number of repetitions performed in a set, and the percentage of 1RM actually used for that number of repetitions.
carbohydrate
A polyhydroxy aldehyde or ketone, or substance that yields such a compound on hydrolysis. Many carbohydrates have the empirical formula (CH2O)n; some also contain nitrogen, phosphorus, or sulfur. // A polyhydroxyl aldehyde or ketone. // An organic compound composed of carbon, hydrogen, and oxygen, with the hydrogen and oxygen present in a 2:1 ratio; carbohydrates include starches, sugars, and cellulose. // A compound composed of carbon, hydrogen, and oxygen. // A molecule consisting of carbon, hydrogen, and oxygen in the proportions 1:2:1; a molecule of sugar or a macromolecule composed of sugar subunits. // An organic molecule composed of carbon, hydrogen, and oxygen. // Polyhydroxy aldehydes or ketones. Carbohydrates can be either simple sugars, such as glucose, or complex sugars, such as cellulose.
catabolism
The phase of intermediary metabolism concerned with the energyyielding degradation of nutrient molecules. // Breakdown of complex molecules into simple molecules. // All decomposition reactions in a living organism; the breakdown of complex organic compounds into simpler ones. // Process of breakdown of complex molecules into simpler ones often providing biologically available energy in the form of ATP. // The breaking down of complex nutrient molecules into simpler molecules; also called catabolic metabolism. See also anabolism. // The group of metabolic pathways that break down larger molecules into smaller ones. // The reactions that break down complex molecules into simpler ones to generate energy directly or indirectly. (Chapter 14)
catalyst
Substance that speeds up a chemical reaction. // Substance that can lower the activation energy of a reaction (thus increasing its rate), without itself being consumed by the reaction. // A substance that increases the rate of a chemical reaction but is not altered itself. // A substance that increases the rate of a chemical transformation by providing an alternative mechanism but is not itself changed in the reaction. // A substance that increases the rate of the reaction but is not consumed by the reaction; it works by providing an alternate mechanism in which the rate-determining step has a smaller activation energy.
cation
Ion with a positive charge; e.g., Na+. // A positively charged ion.
centromere
The nonstaining constriction of a chromosome that is the point of attachment of the spindle fiber. // Constricted region of a mitotic chromosome that holds sister chromatids together. This is also the site on the DNA where the kinetochore forms so as to capture microtubules from the mitotic spindle. // The region of the chromosome that interacts with microtubules during mitosis. // A specialized site in a chromosome, serving as the attachment point for the mitotic or meiotic spindle. // Spindle-fiber attachment region of a chromosome.
chaperone // molecular chaperone // chaperone protein
A protein that helps nascent polypeptides fold into their proper three-dimensional structures. // Any of several classes of proteins or protein complexes that catalyze the accurate folding of proteins in all cells. // A protein that assists in the folding of other proteins. // A protein that facilitates the folding of other polypeptide chains, the assembly of multimeric proteins, or the formation of macromolecular assemblies (e.g., chromatin). Also called molecular chaperone. (Chapters 4, 12, and 13) // Protein that helps guide the proper folding of other proteins, or helps them avoid misfolding. Includes heat-shock proteins (hsp). // A protein that can fold or unfold other molecules. These proteins bind reactive trace elements and ferry them to different parts of the cell for delivery.
chemotaxis
Movement of cell or organism in response to chemicals. // Attraction or repulsion of organisms by a diffusing substance. // Movement of a cell toward or away from some diffusible chemical. // A cell’s sensing of and movement toward or away from a specific chemical agent. // Cellular movement occurring in response to chemical signals in the environment. // Movement in response to the presence of a chemical.
chloroplast
Organelle in green algae and plants that contains chlorophyll and carries out photosynthesis. // The organelle that performs photosynthesis in photoautotrophic eukaryotes. // A green organelle in the cytoplasm of plants that contains chlorophyll and in which starch is synthesized. A mode of cytoplasmic inheritance, independent of nuclear genes, has been associated with these cytoplasmic organelles. // Chlorophyll-containing photosynthetic organelle in some eukaryotic cells. // Important compartment of plant cells; site of photosynthesis; chloroplasts have their own DNA replication, transcription, and ribosomes. Originated from cyanobacteria.
chromatin
Genetic material of the nucleus in a nondividing cell. // A filamentous complex of DNA, histones, and other proteins, constituting the eukaryotic chromosome. // Complex of DNA, histones, and non-histone proteins found in the nucleus of a eukaryotic cell. The material of which chromosomes are made. // DNA complexed with histones. // The complex of DNA and proteins in eukaryotic chromosomes; originally named because of the readiness with which it stains with certain dyes. // The three-dimensional molecular structure of DNA and proteins in the nuclei of cells. // Threadlike, uncondensed DNA in an interphase eukaryotic cell.
chromosome
The most compact form of genetic material; a single long molecule of DNA and associated proteins; becomes visible only when the cell is dividing. // Structure composed of a very long DNA molecule and associated proteins that carries part (or all) of the hereditary information of an organism. Especially evident in plant and animal cells undergoing mitosis or meiosis, during which each chromosome becomes condensed into a compact rodlike structure visible in the light microscope. // The DNA-containing structures that occur in the nuclei of living cells. // The structure that carries hereditary information, chromosomes contain genes. // A single large DNA molecule and its associated proteins, containing many genes; stores and transmits genetic information. // A structure in the cell nucleus containing a single linear thread of DNA. // Darkly staining nucleoprotein bodies that are observed in cells during division. Each chromosome carries a linear array of genes.
citric acid cycle [tricarboxylic acid (TCA) cycle, Krebs cycle]
A cyclic pathway for the oxidation of acetyl residues to carbon dioxide, in which formation of citrate is the first step; also known as the Krebs cycle or tricarboxylic acid cycle. // A cyclic metabolic pathway that occurs in the matrix of mitochondria during which energy in the bonds of acetyl CoA is transferred to form ATP, NADH, and FADH2. // The metabolic pathway by which acetyl CoA is degraded to CO2. // Central metabolic pathway found in aerobic organisms. Oxidizes acetyl groups derived from food molecules, generating the activated carriers NADH and FADH2, some GTP, and waste CO2. In eukaryotic cells, it occurs in the mitochondria. // An alternative name for the citric acid cycle by which acetyl CoA is degraded to CO2. // A pathway that converts two-carbon compounds to CO2, transferring electrons to NAD+ and other carriers; also called tricarboxylic acid (TCA) cycle or critic acid cycle. // An alternative name for the citric acid cycle, by which acetyl CoA is degraded to CO2.
class switching, class switch recombination
Ability of a B cell to produce a different class of antibody against one antigen. // A change in the class of the immunoglobulin expressed by a B lymphocyte. // Change from making one class of immunoglobulin (for example, IgM) to making another class (for example, IgG) that many B cells undergo during the course of an adaptive immune response. Involves DNA rearrangements called class-switch recombination. // A somatic gene recombination process in activated B cells that replaces one heavy-chain constant region with one of a different isotype, switching the isotype of antibodies from IgM to the production of IgG, IgA, or IgE. This affects the antibody effector functions but not their antigen specificity. Also known as isotype switching. Cf. somatic hypermutation. // An irreversible change at the DNA level when a B cell switches from making IgM and IgD to making one of the secondary classes of immunoglobulin.
clone
A population of cells all derived from the same progenitor cell. // A population of genetically identical cells that are descended from the same ancestral cell. // A population of cells arising from a single parent cell. // All the individuals derived by vegetative propagation from a single original individual. In molecular biology, a population of identical DNA molecules all carrying a particular DNA sequence from an organism. // The descendants of a single cell.
codon
A base triplet on messenger RNA that specifies an amino acid. // A sequence of three bases in a nucleic acid that codes for one amino acid. // Group of three nucleotide bases in a messenger RNA molecule. // A sequence of three adjacent nucleotides in a nucleic acid that codes for a specific amino acid. // A sequence of three nucleotides in mRNA that specifies the insertion of an amino acid into a polypeptide. // A set of three adjacent nucleotides in an mRNA molecule that specifies the incorporation of an amino acid into a polypeptide chain or that signals the end of polypeptide synthesis. Codons with the latter function are called termination codons. // A three-base sequence on a messenger RNA chain that encodes the genetic information necessary to cause a specific amino acid to be incorporated into a protein. Codons on mRNA are read by complementary anticodons on tRNA. // Sequence of three nucleotides in a DNA or mRNA molecule that represents the instruction for incorporation of a specific amino acid into a growing polypeptide chain. // Three contiguous bases in an mRNA template that specify the amino acids incorporated into protein. (Chapter 11)
coenzyme
Organic molecules assisting in enzyme function; e.g., NAD+. // A substance necessary for the activity of an enzyme. // Small molecule tightly associated with an enzyme that participates in the reaction that the enzyme catalyzes, often by forming a covalent bond to the substrate. Examples include biotin, NAD+, and coenzyme A. // A nonprotein substance that is associated with and that activates an enzyme. // A small organic molecule that acts as a cofactor in a biological reaction. // An organic cofactor required for the action of certain enzymes; often has a vitamin component.
cortex
Outer region of an organ; e.g., cerebral cortex, adrenal cortex. // The cytoskeletal network in the cortical region of the cytosol just beneath the plasma membrane. // The protective fungal covering of a lichen. // Any collection of neurons that forms a thin sheet, usually at the brain’s surface. // The outer part of a tissue or organ; in lymph nodes it refers to the follicles, which are mainly populated by B cells.
covalent bond
A bond in which an electron pair is equally shared by protons in two adjacent atoms. // A chemical bond that involves sharing of electron pairs. // A bond formed by sharing electrons between atoms. // A chemical bond in which the electrons of one atom are shared with another atom. // A chemical bond in which two atoms share electrons that interact with the nuclei of both atoms, lowering the potential energy of each through electrostatic interactions. // Stable chemical link between two atoms produced by sharing one or more pairs of electrons. // Strong chemical bond formed by a binding electron pair. // Chemical bond formed when atoms share electrons.
cyclic adenosine monophosphate (cAMP) // cyclic AMP (cAMP, adenosine 3’, 5’-cyclic monophosphate)
A second messenger formed from adenosine triphosphate by the action of the enzyme adenylyl cyclase. // A second messenger of many hormones. // A second messenger used when some hormones or neurotransmitters act on a target cell. Formed when adenylate cyclase reacts with ATP. // Adenosine-3′, 5′-monophosphate, a small molecule that must be bound by the catabolite activator protein (CAP) in order for the complex (CAP/cAMP) to bind to the promoters of operons and stimulate transcription. // A second messenger; its formation in a cell by adenylyl cyclase is stimulated by certain hormones or other molecular signals. // A molecule derived from ATP, in which the phosphate group has a cyclic structure; acts as a cellular messenger. // Nucleotide that is generated from ATP by adenylyl cyclase in response to various extracellular signals. It acts as a small intracellular signaling molecule, mainly by activating cAMP-dependent protein kinase (PKA). It is hydrolyzed to AMP by a phosphodiesterase. (Figure 15–25)
cytokine
Protein that regulates and facilitates immune system activity. // Extracellular signal protein or peptide that acts as a local mediator in cell–cell communication. // One of a family of small secreted proteins (such as interleukins or interferons) that activate cell division or differentiation by binding to plasma membrane receptors in target cells. // A small protein released from human cells that regulates the immune response; directly or indirectly may induce fever, pain, or T cell proliferation. // Biologically active proteins released by activated lymphocytes and monocytes/macrophages. // Proteins made by a cell that affect the behavior of other cells, particularly immune cells. Cytokines made by lymphocytes are often called interleukins (abbreviated IL). Cytokines and their receptors are listed in Appendix III. Cf. chemokines. // Soluble proteins produced by cells in response to various stimuli, including virus infection; they aff ect the behavior of other cells both locally and at a distance, by binding to specifi c cytokine receptors. (Chapters 3 and 4)
cytoplasm
The portion of a cell’s contents outside the nucleus but within the plasma membrane; includes organelles such as mitochondria. // All cellular contents contained between the plasma membrane and the nucleus; includes cytosol, organelles, and inclusions. // Basic compartment of the cell (surrounded by the plasma membrane) in which nucleus, endoplasmic reticulum, mitochondria and other organelles are embedded. // Cellular material contained by the cell membrane, including the organelles but excluding the nucleus. // Contents of a cell that are contained within its plasma membrane but, in the case of eukaryotic cells, outside the nucleus. // In a prokaryotic cell, everything inside the plasma membrane; in a eukaryotic cell, everything inside the plasma membrane and external to the nucleus. // The protoplasm of a cell outside the nucleus in which cell organelles (mitochondria, plastids, and the like) reside; all living parts of the cell except the nucleus.
cytoskeleton
The filamentous network that provides structure and organization to the cytoplasm; includes actin fi laments, microtubules, and intermediate filaments. // Organized network of protein filaments and hollow tubules that provide organization, support, and movement of the cell. // A complex system of fibers and filaments that provides support for cells and that is involved in moving the components of cells throughout the cytoplasm. // Microfilaments, intermediate filaments, and microtubules that provide support and movement for eukaryotic cytoplasm. // System of protein filaments in the cytoplasm of a eukaryotic cell that gives the cell shape and the capacity for directed movement. Its most abundant components are actin filaments, microtubules, and intermediate filaments. // The internal scaffolding that gives a cell its characteristic shape; consists of microtubules, neurofilaments, and microfilaments. cytosol The watery fluid inside a cell. // The intracellular structural network composed of actin filaments, microtubules, and intermediate filaments. // The network of filamentous protein structures along which vesicles and organelles are moved and which are ultimately required for cell shaping.
cytosol
The continuous aqueous phase of the cytoplasm, with its dissolved solutes; excludes the organelles such as mitochondria. // Contents of the main compartment of the cytoplasm, excluding membrane-bounded organelles such as endoplasmic reticulum and mitochondria. // One of several major compartments within cells containing elements such as the cytoskeleton, and mitochondria, and separated by membranes from distinct compartments such as the nucleus and vesicular system. // The fluid portion of cytoplasm. // The viscous, syruplike fluid medium with dissolved solutes in the cytoplasm.
deamination
The enzymatic removal of amino groups from biomolecules such as amino acids or nucleotides. // Process of removing the amine group of an amino acid. // The removal of an amino group from an amino acid to form ammonia. See also ammonification. // The removal of amino groups from compounds, particularly amino acids, with the production of urea. // The removal of an amino group from a molecule, as occurs with amino acids during metabolic degradation. // Destruction of a protein’s or nucleic acid’s higher-order structure. // Loss of native configuration of a macromolecule, usually accompanied by loss of biological activity. Denatured proteins often unfold their polypeptide chains and express changed properties of solubility. // Partial or complete unfolding of the specific native conformation of a polypeptide chain, protein, or nucleic acid such that the function of the molecule is lost. // A change in a protein’s complex three-dimensional shape that causes its biological activity to be impaired or to cease; may occur with changes in pH or increased temperature.// A change in the molecular structure of a protein, usually making it nonfunctional.
deoxyribonucleic acid (DNA)
The nucleic acid of genetic material in all cells and some viruses. // A double-stranded molecule constructed from four nucleic acids that contains the genetic instructions for a cell. // Chemical carriers of a cell’s genetic information. // Polynucleotide formed from covalently linked deoxyribonucleotide units. The store of hereditary information within a cell and the carrier of this information from generation to generation. // The biopolymer consisting of deoxyribonucleotide units linked together through phosphate–sugar bonds. Found in the nucleus of cells, DNA contains an organism’s genetic information. // A doublestranded nucleic acid, composed of deoxyribonucleotide monomers; directs protein synthesis. // Deoxyribonucleic acid; the information-carrying genetic material that comprises the genes. DNA is a macromolecule composed of a long chain of deoxyribonucleotides joined by phosphodiester linkages. Each deoxyribonucleotide contains a phosphate group, the five-carbon sugar 2-deoxyribose, and a nitrogen-containing base. // Deoxyribonucleic acid, the biomolecule in cells that stores the genetic information; composed of 2 complementary nucleic acid strands bonded by G-C and A-T pairs. // Deoxyribonucleic acid; the genetic blueprint from which proteins are synthesized. A double-stranded helix of nucleotides. // A polynucleotide with a specific sequence of deoxyribonucleotide units covalently joined through 3’,5’-phosphodiester bonds; serves as the carrier of genetic information.
differentiation
Process by which a cell undergoes a change to an overtly specialized cell type. // A process in which unspecialized cells develop characteristic structures and functions. // During embryonic development, the process by which structures become more complex and functionally specialized. // Process in which cells lose their omnipotence to adopt more specialized functions. // Specialization of cell structure and function during growth and development. // The process of dissecting skill into subunits and determining where errors are.
diffusion
The net drift of molecules through space due to random thermal movements. // The net movement of molecules in the direction of lower concentration. // The net movement of molecules or ions from an area of higher concentration to an area of lower concentration. // Random movement of molecules or particles down their concentration gradient. // Movement of molecules through a domain, from an area of high concentration to one of low concentration, by random molecular movement. // The process by which gas molecules spread out in response to a concentration gradient. // The temperature-dependent movement of molecules from regions of high concentration to regions of low concentration, resulting in a more even distribution.
disaccharide
A carbohydrate consisting of two covalently joined monosaccharide units. // Carbohydrate composed of two monosaccharides; e.g., sucrose. // A carbohydrate composed of two monosaccharides. // A sugar consisting of two simple sugars, or monosaccharides. // A carbohydrate formed by linking two simple sugars through an acetal bond. // Carbohydrate molecule composed of two monosaccharides linked by a chemical bond. distal convoluted tubule (DCT) The part of the renal nephron between the loop of Henle and the collecting duct system.
DNA polymerase
An enzyme that catalyzes template-dependent synthesis of DNA from its deoxyribonucleoside 5’-triphosphate precursors. // Enzyme that synthesizes DNA by copying a DNA template. // An enzyme that catalyzes the synthesis of DNA. // Enzyme that synthesizes DNA by joining nucleotides together using a DNA template as a guide. // DNA-synthesizing enzymes.
edema
Localized swelling of a tissue. // Swelling caused by the entry of fluid and cells from the blood into the tissues; it is one of the cardinal features of inflammation. // Abnormal fluid accumulation in the interstitial tissue spaces. // An abnormal accumulation of interstitial fluid in tissues, causing swelling. // Swelling of interstitial spaces with fluid that results in excess of accumulation of water in the tissues.
electrophoresis
Movement of charged solutes in response to an electrical field; often used to separate mixtures of ions, proteins, or nucleic acids. // The migration of suspended particles in an electric field. // A technique used for separating charged organic molecules, particularly proteins and DNA fragments. The mixture to be separated is placed on a buffered gel or paper, and an electric potential is applied across the ends of the apparatus. Negatively charged molecules migrate toward the positive electrode, and positively charged molecules migrate toward the negative electrode. // Separation of molecules in an electrical field. // Separation technique based on the mobility of analytes in an electric field. Important techniques are one- and two-dimensional gel electrophoresis and capillary electrophoresis.
endergonic // endergonic reaction
A reaction that has a positive freeenergy change and is therefore nonspontaneous. In an energy diagram, the product of an endergonic reaction has a higher energy level than the reactants. // A chemical reaction that consumes energy (that is, for which DG is positive). // A chemical reaction that requires energy. // Reaction with positive ΔG. // Chemical reaction that requires the input of energy.
endocytosis
Movement of substances from the extracellular environment into the cell through the formation of a vesicle. // The process by which material is moved into a eukaryotic cell. // The uptake of extracellular material by its inclusion in a vesicle (endosome) formed by invagination of the plasma membrane. // Uptake of material into a cell by an invagination of the plasma membrane and its internalization in a membraneenclosed vesicle. See also pinocytosis and phagocytosis. endoderm Embryonic tissue that is the precursor of the gut and associated organs. // Cellular uptake of soluble macromolecules or particles through an endocytic vesicle. // The process by which a bit of the cell membrane is pinched off, internalized, and converted to an intracellular vesicle. See also exocytosis.
endoplasmic reticulum (ER)
An extensive system of double membranes in the cytoplasm of eukaryotic cells; it encloses secretory channels and is often studded with ribosomes (rough endoplasmic reticulum). // Cellular endomembrane system in which proteins are modified posttranslationally. // Membranous portion of a cell where protein synthesis and lipid synthesis occur. // Network of membranes in the cytoplasm to which ribosomes adhere. // A membranous network in eukaryotic cells connecting the plasma membrane with the nuclear membrane. // Labyrinthine membranebounded compartment in the cytoplasm of eukaryotic cells, where lipids are synthesized and membrane-bound proteins and secretory proteins are made. // Organelle composed of an extensive network of connected membranes; involved in synthesis, transport, and storage of macromolecules, and detoxification of drugs: present as smooth ER or rough ER.
enzyme
A biomolecule, either protein or RNA, that catalyzes a specific chemical reaction. It does not affect the equilibrium of the catalyzed reaction; it enhances the rate of the reaction by providing a reaction path with a lower activation energy. // Protein that catalyzes a chemical reaction by lowering the activation energy. // A biochemical catalyst made of protein that increases the rates of biochemical reactions. // A biological catalyst. Enzymes are large proteins that catalyze specific biochemical reactions. // A molecule that catalyzes biochemical reactions in a living organism, usually a protein. See also ribozyme. // A protein compound that speeds a chemical reaction. // A protein that accelerates a specific chemical reaction in a living system. // A protein that facilitates a biochemical reaction by lowering the energy required. // Protein that catalyses a chemical reaction, e.g., the hydrolysis of acetylcholine. // Protein that catalyzes a specific chemical reaction.
eukaryote
A unicellular or multicellular organism with cells having a membranebounded nucleus, multiple chromosomes, and internal organelles. // A cell having DNA inside a distinct membrane-enclosed nucleus. // A member of the large group of organisms that have nuclei enclosed by a membrane within their cells (cf. Prokaryote). // Organism composed of one or more cells that have a distinct nucleus. Member of one of the three main divisions of the living world, the other two being bacteria and archaea. // Cells with a membrane-bounded nucleus.
Exergonic // exergonic reaction
A reaction that has a negative freeenergy change and is therefore spontaneous. On an energy diagram, the product of an exergonic reaction has a lower energy level than that of the reactants. // A chemical reaction that proceeds with the release of free energy (that is, for which DG is negative). // A chemical reaction that releases energy. // Chemical reaction in which chemical energy is released. // Reaction with negative ΔG.
exocytosis
Process whereby contents within a vesicle are exported outside a cell. // Excretion of material from the cell by vesicle fusion with the plasma membrane; can occur constitutively or be regulated. // Secretion of water-soluble substances by fusion of an exocytic vesicle with the plasma membrane. // The fusion of an intracellular vesicle with the plasma membrane, releasing the vesicle contents to the extracellular space. // The process whereby material is released from an intracellular vesicle into the extracellular space by fusion of the vesicle membrane with the cell membrane. See also endocytosis.
exon
The segment of a eukaryotic gene that encodes a portion of the final product of the gene; a segment of RNA that remains after posttranscriptional processing and is transcribed into a protein or incorporated into the structure of an RNA. See also intron. // A portion of a DNA molecule that codes for a section of the future messenger RNA molecule; these “coding” regions in pre-messenger RNA are joined together to form mature messenger RNA. // Segment of a eukaryotic gene that consists of a sequence of nucleotides that will be represented in mRNA or in a final transfer, ribosomal, or other mature RNA molecule. In protein-coding genes, exons encode the amino acids in the protein. An exon is usually adjacent to a noncoding DNA segment called an intron. // A region of a eukaryotic chromosome that encodes a protein. // A section of DNA that contains genetic information. // Blocks of noncontiguous coding sequences (generally short) present in many cellular and viral pre-mRNAs. (Chapter 10) // The portion of RNA transcribed from the DNA that is translated into a protein. // The parts of the gene that are represented in the mature RNA. // The segments of a eukaryotic gene that correspond to the sequences in the final processed RNA transcript of that gene.
feedback inhibition // end-product inhibition
Inhibition of a metabolic pathway by its end product. // Inhibition of an allosteric enzyme at the beginning of a metabolic sequence by the end product of the sequence; also known as end-product inhibition. // Inhibition of an enzyme in a particular pathway by the accumulation of the end-product of the pathway; also called endproduct inhibition. // The process in which a product of a reaction feeds back to inhibit a previous reaction in the same pathway. // The accumulated end product of a biochemical pathway stops synthesis of that product. A late metabolite of a synthetic pathway regulates synthesis at an earlier step of the pathway.
Flagellum (pl, flagella; adj flagellate)
(flă-jel′-ŭm; pl., flagella, -ă) Whiplike locomotory extension of the plasma membrane; enables a sperm cell to move. // A cell appendage used in propulsion. Bacterial flagella have a much simpler structure than eukaryotic flagella, which are similar to cilia. // A whiplike organelle of locomotion in certain cells; locomotor structures in flagellate protozoa. // Long, whiplike protrusion whose undulations drive a cell through a fluid medium. Eukaryotic flagella are longer versions of cilia. Bacterial flagella are smaller and completely different in construction and mechanism of action. Compare cilium. // A thin appendage from the surface of a cell; used for cellular locomotion; composed of flagellin in prokaryotic cells, composed of 9 + 2 microtubules in eukaryotic cells.
G protein (trimeric GTP-binding protein)
Specific protein that acquires its energy from guanosine triphosphate; when activated by a membrane receptor, it relays the signal to another membrane protein and alters the activity of that protein. // A trimeric GTPbinding protein with intrinsic GTPase activity that couples GPCRs to enzymes or ion channels in the plasma membrane. // A large family of GTP-binding proteins that act in intracellular signaling pathways and in membrane trafficking. Active when GTP is bound, they self-inactivate by converting GTP to GDP. Also called guanosine nucleotide–binding proteins. // Intracellular GTPases that act as molecular switches in signaling pathways. They bind GTP to induce their active conformation, which is lost when GTO is hydrolyzed to GDP. There are two kinds of G proteins: the heterotrimeric (α, β, γ subunits) receptor-associated G proteins, and the small G proteins, such as Ras and Raf, which act downstream of many transmembrane signaling events. // GTP-binding signal transducing proteins that mediate most hormone effects. // A membrane-enclosed protein that binds guanosine triphosphate (GTP) when activated by a membrane receptor. Active G-proteins can stimulate or inhibit other membrane-enclosed proteins.
gene
A chromosomal segment that codes for a single functional polypeptide chain or RNA molecule. // A hereditary determinant of a specific biological function; a unit of inheritance (DNA) located in a fixed position on a chromosome; a segment of DNA encoding one polypeptide and defined operationally by the cis-trans or complementation test. // A length of DNA directing the synthesis of a polypeptide or a functional RNA. // A segment of DNA (a sequence of nucleotides in DNA) encoding a functional product. // A portion of DNA that encodes for a specific protein. // A sequence of codons within a DNA molecule that codes for a single protein. // A unit of heredity; a sequence of DNA that encodes a single polypeptide or protein. // Region of DNA that is transcribed as a single unit and carries information for a discrete hereditary characteristic, usually corresponding to (1) a single protein (or set of related proteins generated by variant post-transcriptional processing), or (2) a single RNA (or set of closely related RNAs). // Segment of DNA containing information to direct synthesis of a specific protein; functional unit of DNA.
genome
One complete copy of the genetic information in a cell. // The totality of genetic information belonging to a cell or an organism; in particular, the DNA that carries this information. // A complete set (n) of chromosomes (hence, of genes) inherited as a unit from one parent. // All the genetic information encoded in a cell or virus. // The entirety of genetic information of an organism necessary for its development and functioning. This information is encoded in deoxyribonucleic acid (DNA). // The total content of an organism’s genetic material.
genotype
The genetic constitution of an individual that, along with environmental influences, contributes to the phenotype. // The genetic constitution of an organism, as distinct from its physical characteristics, or phenotype. // Genetic constitution of an individual cell or organism. The particular combination of alleles found in a specific individual. // The genetic constitution (gene makeup) of an organism (cf. Phenotype). // The genetic makeup of an animal or person. // The genetic makeup of an organism.
glycogen
Polysaccharide formed from glucose monomers. // A highly branched form of starch. // A storage form of carbohydrate that is found in the skeletal muscle and liver. // Carbohydrate storage molecule consisting of branching chains of glucose. // Polysaccharide composed exclusively of glucose units. Used to store energy in animal cells. Large granules of glycogen are especially abundant in liver and muscle cells.
glycolipid
A lipid containing a carbohydrate group. // Lipid with an attached carbohydrate. // A biological molecule in which a carbo hydrate is linked through a glycoside bond to a lipid. // A triglyceride composed of a fatty acid, a hydrocarbon chain, and a sugar molecule as the polar section. // Carbohydrate-containing lipid. // Lipid molecule with a sugar residue or oligosaccharide attached.
glycolysis
First stage of cellular respiration in which glucose is partially catabolized to form pyruvate and transfer energy to form ATP molecules. // A series of ten enzyme-catalyzed reactions that break down glucose into 2 equivalents of pyruvate, CH3COCO2⁻. // The breakdown of glucose to pyruvate in a cell in the absence of oxygen. // The catabolic pathway by which a molecule of glucose is broken down into two molecules of pyruvate. // The main pathway for the oxidation of glucose to pyruvic acid; also called Embden-Meyerhof pathway. // Ubiquitous metabolic pathway in the cytosol in which sugars are incompletely degraded with production of ATP. Literally, “sugar splitting.”
glycoprotein
A protein containing a carbohydrate group. // A biological molecule in which a carbohydrate is linked through a glycoside bond to a protein. // A protein carrying covalently linked sugar chains (oligosaccharides). // A protein containing covalently bound carbohydrate. // Any protein with one or more saccharide or oligosaccharide chains covalently linked to amino acid side chains. Most secreted proteins and most proteins exposed on the outer surface of the plasma membrane are glycoproteins.
Golgi apparatus (Golgi complex)
An organelle that sorts and chemically modifies proteins that are destined for delivery to different parts of the cell. // Cellular organelle that packages macromolecules, such as lipids and proteins destined to become part of plasma membrane or released from the cell. // Series of saclike membranes that act as a center to package, sort, and modify molecules arriving from the endoplasmic reticulum in a transport vesicle. // Complex organelle in eukaryotic cells, centered on a stack of flattened, membraneenclosed spaces, in which proteins and lipids transferred from the endoplasmic reticulum are modified and sorted. It is the site of synthesis of many cell wall polysaccharides in plants and extracellular matrix glycosaminoglycans in animal cells. // An organelle involved in the secretion of certain proteins. // A complex membranous organelle of eukaryotic cells; functions in the posttranslational modification of proteins and their secretion from the cell or incorporation into the plasma membrane or organellar membranes. // A membranous system within cells that is involved in the secretion of cellular substances.
half-life (t₁/₂)
The time required for decay of a molecule or macromolecule to half of the original concentration. // The time required for the disappearance or decay of one-half of a given component in a system. // The time that it takes for half of the substrate molecules to react in a first-order reaction. // Time required to reduce substance by one-half of its original quantity. // The time required for the concentration of a reactant or the amount of a radioactive isotope to fall to one-half of its initial value.
hemoglobin (Hb)
The iron-containing compound in blood that binds oxygen. // A heme protein in erythrocytes; functions in oxygen transport. // Conjugated protein compound containing iron, located in erythrocytes of vertebrates; important in the transportation of oxygen to the cells of the body. // A red-pigmented protein that transports oxygen and carbon dioxide; responsible for characteristic red color of blood. // The iron-containing pigment within red blood cells that binds oxygen for efficient transport.
histone
A protein associated with DNA in eukaryotic chromosomes. // Conserved group of proteins that bind to negatively charged DNA and are part of the nucleosome. Modification of histone proteins are important for epigenetic regulation. // One of a group of small abundant proteins, rich in arginine and lysine, that combine to form the nucleosome cores around which DNA is wrapped in eukaryotic chromosomes. // Group of proteins rich in basic amino acids. They function in the coiling of DNA in chromosomes and in the regulation of gene activity. // Small, basic proteins that are tightly associated with DNA in chromatin. // The family of basic proteins that associate tightly with DNA in the chromosomes of all eukaryotic cells.
