BCH 2333 Lecture Notes - Lecture 13: Activation Energy, Hydrolysis, Hydrolase

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blushcaribou532

7 Mar 2017

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Uncatalyzed reaction has a higher g . = transition state is the highest e structure not a stable compound. Any direction you go from the transition state is energetically downhill, anything it does turns more stable. The relative initial and final states do not change when a catalyst is added. Catalyst is not consumed during the reaction. Intermediates in the reaction = allow the activation energy to be smaller. G approaches 0 interacts with s, p is formed. In this case, rate is limited by how fast and s interact. Linear phase: rate increases as [s] increases. Like ligand binding: enzyme catalyzes formation of product. This step is like a chemical reaction. Most common model for describing enzymes dp = k2. Reversible binding keq = k1 ate of p formation r. *** derive this equation (michaelis-menten) this will be asked of you on the exam *** Assigned an ec number (enzyme commision) which defines exactly which reaction it catalyzes.

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26. An enzymatic reaction proceeds with maximal velocity (Vmax) when A. the enzyme is in excess of the substrate. B. allosteric activators are present. the reaction is proportional to substrate concentration. D. the substrate concentration exceeds that of a noncompetitive inhibitor. E. the enzyme is saturated with substrate 27- 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. 28. An enzyme affects the rate of a chemical reaction by A. decreasing the free energy change of the reaction. B. increasing the free energy change of the reaction. C. lowering the energy of activation of the reaction. D. displacing the equilibrium constant. E. raising the energy of activation of the reaction. 29. Which statement is CORRECT? A. Enzymes are small molecules that are heat stable. B. Enzymes affect rates of reactions in the forward and reverse direction. C. Enzymes will determine whether a reaction will take place. D. Enzymes are permanently altered following the conversion of substrate to product. 30. Which of the following statements is TRUE? Enzyme catalysis of a chemical reaction: A. increases the energy of the transition state. B. decreases the change in free energy of the reaction. C. increases the change in free energy of the reaction. D. decreases the change in the free energy of activation. 31. Which of the following statements about enzyme substrate complexes is TRUE? A. At high substrate concentration the rate of the reaction is first order. B. The enzyme concentration is higher than the substrate concentration under physiological conditions. C. Alteration in the conformation of the enzyme may occur when substrate binds. D. Increase in enzyme concentration does not affect the rate of the reaction. 32. All of the following statements about enzymes are correct EXCEPT A. enzymes are usually protein in nature and cause reactions to occur B. enzymes form complexes with substrates and products C. enzymes affect the rate of reactions and are not permanently altered during a reaction D enzymes can undergo structural modification during a reaction E. enzyme specificity requires specific functional groups on the enzyme and substrate

Can you please answer my questions fast I appreciate it no explanation is needed

B. C. Mixed tive 8. The panereas is protected from digestion by trypsin (a proteolytic enzyme that it produces) because: A. B. C. D. Trypsin works only on denatured proteins Trypsin is specific for plant proteins Trypsin works only at the surface of membranes Trypsin is not activated until it is proteolytically modified 9. The active site of an enzyme is the region that A. binds allosteric regulators of the enzyme. B. is involved in the catalytic reaction of the enzyme C. binds noncompetitive inhibitors of the enzyme D. is inhibited by the presence of a coenzyme or a cofactor 10. According to the induced fit hypochesis of enzyme catalysis,which of the following is corect? A. The binding of the substrate depends on the shape of the active site B. Some enzymes change their structure when activators bind to the enzyme C. A competitive inhibitor can outcompete the substrate for the active site D. The binding of the substrate changes the shape of the enzyme's active site 11. Increasing the substrate concentration in an enzymatic reaction could overcome which of the following? A. denaturization of the enzyme B. allosteric inhibition C competitive inhibition D. saturation of the enzyme activity 12. Zinc, an essential trace element for most organisms, is present in the active site of the enzyme carboxypeptidase. The zinc most likely functions as a(n) A. competitive inhibitor of the enzyme B. noncompetitive inhibitor of the enzyme C. allosteric activator of the enzyme. D cofactor necessary for enzyme activity 13. Some of the drugs used to treat HIV patients are competitive inhibitors of the HIV reverse transcriptase enzyme. Unfortunately, the high mutation rate of HIV means that the virus rapidly acquires mutations with amino acid changes that make them resistant to these competitive inhibitors. Where in the reverse transcriptase enzyme would such amino acid changes most likely occur in drug-resistant viruses? A. in or near the active site B. at an allosteric site Cat a cofactor binding site D. in regions of the protein that determine packaging into the virus capsid the fever is not controlled? When you have a severe fever, what grave consequence may occur if A. destruction of your enzymes' primary structure B. removal of amine groups from your proteins C. change in the tertiary structure of your enzymes D removal of the amino acids in active sites of your enzymes 14.

1. C6H12O6 + 6O2 Ã 6CO2 + 6H2O Glucose is being _____ to _____ and oxygen is being _____ to _____. a. oxidized; carbon dioxide; reduced; water b. oxidized; water; reduced; carbon dioxide Incorrect c. reduced; water; oxidized; carbon dioxide d. reduced; carbon dioxide; oxidized; water

2. Which of the following stages in the breakdown of the piece of toast you had for breakfast generates the most ATP? a. the citric acid cycle Incorrect b. glycolysis c. the digestion of starch to glucose d. oxidative phosphorylation

3. Which of the following is a catabolic pathway? a. gluconeogenesis b. production of starch Incorrect c. glycolysis d. production of glycogen

4. Per molecule, the oxidation of a fatty acid results in _____ energy storage than the oxidation of glucose. a. the same b. less Incorrect c. more d. None of the above; fatty acids cannot be oxidized.

5. Of the eight reactions in the citric acid cycle, how many are oxidation-reduction reactions? a. one b. two c. three d. four e. five

6. The process of glycolysis transfers the energy in sugar molecules into the stored energy of activated carriers such as ATP and NADH. Which statement is true about glycolysis? a. Only eukaryotic organisms do glycolysis. b. The ten reactions of glycolysis are identical in all eukaryotic cells, but are different in prokaryotic cells due to their diverse metabolic strategies. Incorrect c. The ten reactions of glycolysis are identical in almost all living organisms on the planet. d. There are many ways to oxidize glucose and transfer energy into activated carriers; the diversity of organisms on the planet is reflected in the diversity of their mechanisms of glycolysis.

7. Referring to the sentence completed in #13 above, the purpose of the latter reaction (in active muscle cells) is to _____. a. accumulate lactic acid in the cell, which provides additional energy for the production of ATP Incorrect b. slow down glycolysis until oxygen becomes available again c. accelerate the Krebs cycle, which will restore the oxygen supply d. regenerate NAD+ so that glycolysis can continue in the absence of oxygen

8. What are the products of the citric acid cycle? a. carbon dioxide, NADH, FADH2 and GTP b. carbon dioxide, NAD+, FAD and GTP c. NADH, FADH2, and acetyl CoA Incorrect d. carbon dioxide and water

9. Which statement is true about enzymes? a. Enzymes catalyze chemical reactions because they make inherently endergonic reactions exergonic. b. Each enzyme in a cell can catalyze many different chemical reactions involving chemically different substrates. Incorrect c. Enzymes can only catalyze reactions in one direction. d. After catalyzing a reaction, an enzyme is permanently altered and can no longer bind substrate. e. None of the above is true. 1

10. âG measures the change in free energy in a system as it converts reactant (Y) into product (X). When [X] = [Y], âG is equal to _____. a. RT b. ÎGÂ° + RT c. ÎGÂ° d. ln [X]/[Y]

11. The âGÂ° for the hydrolysis of ATP is -7.3 kcal/mol. What conditions in the cell would lead to a âG for ATP hydrolysis of -11 kcal/mol? a. An increase in the ATP/ADP ratio b. An increase in anabolic activity in the cell c. Transport of ATP out of the compartment where the reaction is occurring Incorrect d. A decrease in the ATP/ADP ratio

12. In the first reaction of glycolysis, a phosphate transferred from ATP to a glucose molecule to produce glucose-6-phosphate and ADP. Under conditions existing in the cell, the free energy change for this reaction is -8.0 kcal/mole. Which of the following statements is true? Recall that the âGÂ° for the hydrolysis of ATP is -7.3 kcal/mol. a. Glucose concentrations in the cell are always low, making this reaction more favorable than would be expected. b. This reaction is less favorable than would be expected, given the âGÂ° of ATP hydrolysis. c. Glucose-6-P concentrations in the cell are very low relative to glucose concentrations, making the reaction more favorable than would be expected. d. The âGÂ° for the addition of a phosphate to glucose must be -0.7 kcal/mole.

13. Protein E can bind to two different proteins, S and I. The binding reactions are described by the following equations and values: E + S --> ES Keq for ES = 10 E + I> EI Keq for EI = 2 Given the equilibrium constant values, which one of the following statements is true? a. When S is present in excess, no I molecules will bind to E. b. E binds I more tightly than S. c. The binding energy of the ES interaction is greater than that of the EI interaction. d. Changing an amino acid on the binding surface of I from a basic amino acid to an acidic one will probably make the free energy of association with E more negative.

BCH 2333 Lecture Notes - Lecture 13: Activation Energy, Hydrolysis, Hydrolase

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