Sample Questions (Multiple choice) Enzymes & kinetics Which of the following statements is not true regarding the active site of an enzyme? a) An active site is normally a hollow or cleft on the surface of an enzyme b) An active site is normally hydrophilic in nature c) Substrates fit into active sites and bind to functional groups within the active site d) An active site contains amino acids which are important to the binding process and the catalytic mechanism e) none of the above Which of the following statements best describes an allosteric binding site? a) It is a binding site containing amino acids with aliphatic side chains b) It is a binding site that can accept a wide variety of differently shaped molecules c) It is a binding site, other than the active site, that affects the activity of an enzyme when it is occupied by a modulator d) It is a description of an active site which has undergone an induced fit e) none of the above Which of the following terms best describes a drug that binds to an active site and inhibits the enzyme, and where inhibition decreases when substrate concentration is increased? a) allosteric inhibitor b) non-competitive, irreversible inhibitor c) competitive, reversible inhibitor d) suicide substrate e) none of the above Which of the following terms best describes a drug which inhibits the enzyme, but binds to a binding site other than the active site? a) allosteric inhibitor b) irreversible inhibitor c) reversible inhibitor d) Suicide substrate e) none of the above Which of the following statements is incorrect with respect to an enzyme's ability to catalyze a reaction? a) an enzyme provides a reaction surface and a hydrophilic environment for the reaction to take place b) an enzyme binds reactants such that they are positioned correctly and can attain their transition state configurations c) an enzyme allows the reaction to go through a more stable transition state than would normally be the case d) an enzyme can weaken bonds in reactants through the binding process e) none of the above Inorganic ions required by some enzymes to catalyze a reaction are a) prosthetic groups b) cofactors c) co-enzymes d) modulators e) none of the above Organic or metalloorganic molecules required by some enzymes to catalyze a reaction on a substrate are a) prosthetic groups b) cofactors c) co-enzymes d) modulators e) none of the above Non-protein organic or inorganic molecule that are covalently bound to the active site of some enzymes and required to catalyze a reaction on a substrate are: a) prosthetic groups b) cofactors c) co-enzymes d) modulators e) none of the above Which of the following is not true of transition state analogues? a) They mimic the transition state of an enzyme catalyzed reaction b) They react irreversibly with the enzyme c) They are bound more strongly than the substrate or the product d) They require the presence of a stable functional group to mimic the functionality present in the transition state e) none of the above 10 Which of the following is not true of suicide inactivators? a) They are activated by the enzyme catalyzed reaction mechanism b) They react irreversibly with the enzyme c) They form a covalent bond with the active site once activated d) They are unreactive until they bind to the active site e) none of the above 11 Enzymes accelerate reactions by _ the activation energy needed for the reaction a) stopping b) raising c) lowering d) binding e) none of the above 12 Enzymes mainly affect one of the following a) Reaction rates b) Reaction equilibria 13 Most enzymes are composed of a) lipids b) carbohydrates c) proteins d) phosphates e) none of the above 14 Enzyme activity is affected by pH Which statement below is not true a) Enzymes have an optimum pH at which their activity is maximal b) Amino acid side chains in the active site may act as weak acids/ bases with critical functions c) Ionized side chains in enzyme may play an essential role in maintaining protein structure d) The pH optimum for the activity of an enzyme is close to the pH of the environment in which the enzyme is normally found e) none of the above 24 The lower the Km value the higher is the affinity of the enzyme to the substrate This statement is a) always true b) always false c) true under certain conditions d) none of the above ... Non-protein organic or inorganic molecule that are covalently bound to the active site of some enzymes and required to catalyze a reaction on a substrate are: a) prosthetic groups b) cofactors c) co-enzymes... bases with critical functions c) Ionized side chains in enzyme may play an essential role in maintaining protein structure d) The pH optimum for the activity of an enzyme is close to the pH of... of the enzyme to the substrate This statement is a) always true b) always false c) true under certain conditions d) none of the above