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70 Cards in this Set
- Front
- Back
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Enzyme catalysis
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Involvement of an organic molecule, usually a protein but in some cases RNA, in speeding up the rate of a specific chemical reaction or class of reactions
page 129 |
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Transition state
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Intermediate stage in a chemical reaction, of higher free energy than the initial state, through which reactants must pass before giving rise to products.
page 130 |
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Catalyst (3 properties)
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Agent that enhances the rate of a reaction by lowering the activation energy without itself being consumed; catalysts change the rate at which a reaction approaches equilibrium, but not the position of equilibrium.
page 131 |
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Ribozymes
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An RNA molecule with catalytic activity
page 150 |
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Prosthetic groups
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Small organic molecule or metal ion component of an enzyme that plays an indispensable role in the catalytic activity of the enzyme
page 132 |
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Substrate specificity
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Ability of an enzyme to discriminate between very similar molecules
page 133 |
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Group specificity
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Ability of an enzyme to act on any of a whole group of substrates as long as they possess some common structural feature
page 133 |
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Initial reaction velocity (v)
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Reaction rate measured over a period of time during which the substrate concentration has not decreased enough to affect the rate and the accumulation of product is still too small to cause any measurable back reaction
page 139 |
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Induced-fit model
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Model postulating that the active site of an enzyme is relatively specific for its substrate before it binds, but even more so thereafter because of conformational change in the enzyme induced by the substrate
page 136 |
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activation energy (EA)
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Energy required to initiate a chemical reaction
page 130 |
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active site
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Region of an enzyme molecule at which the substrate binds and the catalytic event occurs; also called the catalytic site
page 132 |
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catalase
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A common enzyme found in nearly all living organisms exposed to oxygen. It catalyzes the decomposition of hydrogen peroxide to water and oxygen.[1] It is a very important enzyme in protecting the cell from oxidative damage
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coenzymes
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Small organic molecule that unctions along with an enzyme by serving as a carrier of electrons or functional groups
page 230 |
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denaturation
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Loss of the natural thre-dimensional structure of a macromolecule, usually resulting in a loss of its biological activity; caused by agents such as heat, extremes of pH, urea, salt, and other chemicals
page 32 |
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enzyme kinetics
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Quantitative analysis of enzyme reaction rates and the manner in which they are influenced by a varieety of factors
page 138 |
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hydrogenation
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Addition of electrons plus hydrogen ions (protons) to an organic molecule; reduction.
page 229 |
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homeotherms
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an organism that maintains its body temperature at a constant level, usually above that of the environment, by its metabolic activity.
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lock-and-key model
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Enzymes are proteins that catalyze (i.e., increase the rates of) chemical reactions. In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, called the products.
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maximum velocity (Vmax)
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Upper limiting reaction rate approached by an enzyme-catalyzed reaction as the substrate concentration approaches infinity
page 139 |
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metastable state
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Condition where potential reactants are theremodynamically unstable but have insufficient energy to exceed the activation energy barrier for the reaction
page130 |
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Michaelis constant (Km)
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substrate concentration at which an enzyme-catalyzed reaction is proceeding at one-half of its maximum velocity
page 141 |
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Michaelis-Menten equation
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widely used equation describing the relationship between velocity and substrate concentration or an enzyme-catalyzed reaction
V = Vmax[S]/(km + [S]) page 141 |
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IUB Enzyme Commission, EC system, 6 major classes
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International Union of Biochem.
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saturation
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inability of higher substrate concentrations to increase the velocity of an enzyme-catalyzed reaction beyond a fixed upper limit determined by the finite number of enzyme molecules available
page 139 |
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substrate activation
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role of an enzyme's active site in making a substrate molecule maximally reactive by subjecting it to the appropriate chemical environment for catalysts
page 137 |
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substrate concentration [S]
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amount of substrate present per unit of volume at the beginning of a chemical reaction
page 139 |
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three activation mechanisms
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?
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allosteric effectors
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Small molecule that causes a change in the state of an allosteric protein by binding to a site other than the active site
page 147 |
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allosteric enzymes
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an enzyme exhibiting two alternative forms, each with a different biological property; interconversion of the two states is mediated by the reversible binding of a specific small molecule (allosteric effector) to a regulatory site called the allosteric site
page 147 |
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allosteric (regulatory) site
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region of a protein molecule that is distinct from the active site at which the catalytic event occurs and that binds selectively to a small molecule, thereby regulating the protein's activity
page 147 |
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allosteric inhibitor
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a small molecule whose binding to an enzyme's allosteric site shifts the equilibrium to favor the low-affinity state of the enzyme
page 147 |
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allosteric activatora
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small molecule whose binding to an enzyme's allosteric site shifts the equilibrium to fave the high-affinity state of the enzyme
page 147 |
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active site
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region of an enzyme molecule at which the substrate binds and the catalytic event occurs; also called the catalytic site
page 132 |
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catalytic subunits
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a subunit of a multisubunit enzyme that contains the enzyme's catalytic site
page 147 |
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cooperativity
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property of enzymes possessing multiple catalytic sites in which the binding of a substrate molecule to one catalytic site causes conformational charges that influence the affinity of the remaining sites for substrate
page 148 |
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covalent modification
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type of regulation in which the activity of an enzyme (or other protein) is altered by the addition or removal of specific chemical groups
page 148 |
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competitive inhibitor
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a form of enzyme inhibition where binding of the inhibitor to the active site on the enzyme prevents binding of the substrate and vice versa.
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double-reciprocal plot
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graphic method for analyzing enzyme kinetic data by plotting 1/v versus 1/[S]
page 142 |
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Eadie-Hofstee equation
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alternative to the Lineweaver-Burk equation in which enzyme kinetic data are analyzed by plotting v/{S} versus v
page 143 |
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feedback (end-product) inhibition
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ability of the end product of a biosynthetic pathway to inhibit the activity of the first enzyme in the pathway, thereby ensuring that the functioning of the pathway is sensitive to the intracellular concentration of its product
page 146 |
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irreversible inhibitor
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molecule that binds to an enzyme covalently, causing an irrevocable loss of catalytic activity
page 145 |
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noncompetitive inhibitor
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Non-competitive inhibition is a type of enzyme inhibition where the inhibitor reduces the activity of the enzyme and binds equally well to the enzyme whether or not it has already bound the substrate.
If the inhibitor may bind to the enzyme whether or not the substrate has already been bound, but has a higher affinity for binding the enzyme in one state or the other, it is called a mixed inhibitor. |
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positive v negative cooperativity
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protein kinase
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any of numerous enzymes that catalyze the phosphorylation of protein molecules
page 148 |
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protein phosphatase
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any of numerous enzymes that catalyze the dephosphorylation, or removal by hydrolysis, of phosphate groups from a variety of target proteins
page 148 |
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phosphorylation
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addition of a phosphate group
page 148 |
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phosphorylase a
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phosphorylase kinase
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a serine/threonine-specific protein kinase which activates glycogen phosphorylase to release glucose-1-phosphate from glycogen.
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Phosphorylase b
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?
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regulatory subunits
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a subunit of a multisubunit enzyme that contains an allosteric site
page 147 |
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reversible inhibitor
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molecule that causes a reversible loss of catalytic activity when bound to an enzyme; upon dissociation of the inhibitor, the enzyme regains biological function
page 145 |
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substrate-level regulation
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enzyme regulation that depends directly on the interactions of substrates and products with the enzyme
page 146 |
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substrate analogues
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chemical compounds with a chemical structure that resemble the substrate molecule in an enzyme-catalyzed chemical reaction.
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turnover number (kcat)
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rate at which substrate molecules are converted to product by a single enzyme molecule when the enzyme is operating at its maximum velocity
page 142 |
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Lineweaver-Burk equation
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linear equation obtained by inverting the Michaelis-Menten equation, useful in determining parameters Vmax and Km and in the analysis of enzyme inhibition.
page 142 |
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dephosphorylation
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removal of a phosphate group
page 148 |
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autocatalysis
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catalysis of a reaction by one of its products.
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duodenum
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the first part of the small intestine immediately beyond the stomach, leading to the jejunum.
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enterokinase
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enzyme in the intestinal juice that converts inactive trypsinogen into active trypsin
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glycogen synthase
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Glycogen synthase (UDP-glucose-glycogen glucosyltransferase') is an enzyme involved in converting glucose to glycogen. It takes short polymers of glucose and converts them into long polymers.
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phosphorylase phosphatase
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In enzymology, a [phosphorylase] phosphatase is an enzyme that catalyzes the chemical reaction
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peptidyl transferase
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enzymatic activity, exhibited bye the rRNA of the large ribosomal subunit, that catalyzes peptide bond formation during protein synthesis
page 688 |
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pancreas
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a large gland behind the stomach that secretes digestive enzymes into the duodenum. Embedded in the pancreas are the islets of Langerhans, which secrete into the blood the hormones insulin and glucagon.
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proteolytic cleavage
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removal of a portion of a polypeptide chain, or cutting a polypeptide chain into two fragments, by an enzyme that cleaves peptide bonds
page 149 |
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ribosomes
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small particle composed of rRNA and protein that functions as the site of protein synthesis in the cytoplasm o fprokaryotes and in the cytoplasm, mitochondria, and chloroplasts of eukaryotes; composed of large and small subunits
page 94, 679 |
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trypsin
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a digestive enzyme that breaks down proteins in the small intestine. It is secreted by the pancreas in an inactive form, trypsinogen.
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trypsinogen
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an inactive substance secreted by the pancreas, from which the digestive enzyme trypsin is formed in the duodenum.
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zymogen
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an inactive substance that is converted into an enzyme when activated by another enzyme.
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hexapeptide
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A Hexapeptide is a chain of six amino acids that stimulates cell activity by interacting with targeted molecules,
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