BCCB2003 Lecture Notes - Lecture 7: Tyrosine, Amine, Phosphatase

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1 Aug 2018

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How activity of enzymes is controlled: reversible, we can modify the enzymes affecting the rate at which the reaction proceeds: Binding of a modulator at one site will either: Covalent modification: mostly reversible, enzyme which catalysis transfer of phosphoryl group from atp to acceptor enzyme, used in almost every metabolic process in eukaryotic cells, enzyme which catalyses dephosphorolation of enzyme, phosphatase, phosphoryl group, donor molecule: Typically atp: terminal phosphoral group transferred to a specific amino acid residue on the enzyme, eukaryotes: Three possible acceptor residues: serine, threonine, tyrosine, only occurs intracellularly, example, phosphorylation, control the amount of enzyme that is present in the cell: Synthesis more enzymes when a greater activity is required. Knowing that enzymes present are degraded over time. Proteins are continuously turned over (continuous breaking and reforming of proteins) Enzymes usually have short life spans (quick responses): regulation is flexible to adapt to external signals in a variable environment.

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33-To stabilize the transition state complex, which of the following must be lowered? A) Initial energy state B) Activation energy C) Net energy change D) The Vmax B) Final energy state 34- Which of the following statements about allosteric enzymes is CORRECT? A The binding of substrate to any active site affects the other active sites B The plot of initial velocity vs. substrate concentration is a straight line C The Keq of the reaction is increased when allosteric activator is bound D The enzymes contains only one polypeptide chain E Allosteric activators bind to all active sites equally 35. Which statement about the two different models proposed to explain enzyme specificity is CORRECT. a. The substrate changes shape when enzyme binds in the Lock and Key Model. b. The enzyme undergoes a covalent modification when bound to substrate in the Lock and Key Model. c. The active site of the enzyme alternates in conformation between opened and closed in the Induced Fit Model. d. The enzyme changes conformation after binding the substrate in the Induced Fit Model. eÂ·The product structure is altered after it has bound to the enzyme in the Induced Fit Model. 36. An enzymatic reaction proceeds with maximal velocity (Vmax) when A. the substrate concentration is equal to that of a competitive inhibitor. B. allosteric effectors are present. C. the enzyme substrate complex is maximal. D. the substrate concentration exceeds that of a noncompetitive inhibitor. E. all of the substrate is bound to the enzyme. 37. Which of the statements below are incorrect? A With all other factors that modify the rate of the enzyme catalyzed reaction remaining constant as we raise the temperature of an enzyme catalyzed reaction there is an initial increase of velocity with temperature. B. The rate of reaction increases with temperature because there is an increasing number of molecules with sufficient energy to pass over the energy barrier which we call the energy of activation C. Reaction rate increases with temperature until a maximum is reached, when the rate of the reaction will suddenly suddenly fall to zero because the enzyme will be denatured and therefore inactive. D. The reaction rate initially increases as temperature rises owing to increased kinetic energy of the reacting molecules E. Enzymes in crease reaction rates due to their ability to lower the energy barriers for reactions F. None of the above 38- Which of the following is true for the induced fit theory of enzyme action? A. The conformation of the substrate changes before binding to the enzyme. B. The active site changes shape during binding of the substrate C. The substrate fits into a preformed active site through a lock-and-key mechanism. D. Enzymes alternate between conformations where the active site is either open or closed. E. The substrate causes a cleft to form in the enzyme where it subsequently binds

BCCB2003 Lecture Notes - Lecture 7: Tyrosine, Amine, Phosphatase

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