Biol 131 Question Bank Energy & Metabolism

1. Consider a chemical reaction that has a ΔH of -3 and a ΔST of +5.

A.  Which of these values represents the change in bond energy? ____

B.  What does the other value represent? ______

C.  Is the reaction endergonic or exergonic (circle)?

D.  Is the system more or less (circle) disordered as a result of this reaction?

E.  What is the ΔG of the reaction? ______

2. Living organisms require a continual supply of energy to exist because they

A. defy the laws of thermodynamics.

B. convert it into heat energy, which powers biosynthetic reactions.

C. must continually create new molecular bonds.

D. cause the entropy in the universe to decrease.

3. For each of the pairs A–F to the right, circle the more reduced member (#1 or #2) of the pair.

4. Which one of the following statements about enzymes is correct?

A. An enzyme can catalyze a thermodynamically unfavorable reaction.

B. Enzymes are permanently altered after catalyzing a reaction.

C. An enzyme can catalyze many chemically different reactions.

D. An enzyme can bind to many structurally unrelated molecules.

5. Why do cells use enzymes rather than heat to speed up reactions?

A. Heat does not appreciably speed up chemical reactions.

B. Metabolic reactions are only thermodynamically possible with enzymes.

C. Heat only affects certain types of molecules.

D. Enzymes can cause specific chemical changes.

6. A new antibiotic has been developed that acts as a “competitive inhibitor” of a critical bacterial enzyme. Based upon this information would you expect that the antibiotic:

A. will bind to an allosteric site on the enzyme.

B. will bind to the same site on the enzyme as the substrate.

C. chemically reacts with the substrate before binding to the enzyme.

D. covalently binds to the active site of the enzyme to inactivate it.

7. Consider the following 4 reactions:

1. ADP + Pi ® ATP DG = +7.3 kcal/mole

2. glucose-1-phosphate ® glucose-6-phosphate DG = –1.7 kcal/mole

3. glucose + fructose ® sucrose DG = +5.5 kcal/mole

4. glucose ® CO2 + H2O DG = –686 kcal/mole

A. Which of these reactions will NOT occur spontaneously? ______

B. Reaction 4 represents the overall reaction for cellular respiration. Based upon the ΔG of the reaction ADP + Pi ® ATP, ______ATPs could theoretically be produced with the complete oxidation of glucose to CO2. In reality, only 36 ATP are produced in cells during this reaction; what happens to the rest of the energy? ______

8. The graph to the right is an energy diagram for a reaction in which substrate S is converted to product P.

A. Is this an exergonic or endergonic (circle) reaction?

B. Indicate the following on the graph:

1. The activation energy for the reaction

2. The free energy change for the reaction

3. Draw a new curve on the graph to indicate how an enzyme that converts S to P will change the energetics of the reaction.

C. Which of the following reactions might this curve represent?

1. ADP + Pi ® ATP

2. dipeptide ® two amino acids

3. glucose + fructose ® sucrose

Explain:

9. Suppose you were to measure the effect of temperature on the rate of an enzyme-catalyzed reaction.

A. In the space to the right, draw the pattern of enzymatic activity you would expect to find.

B. Why does temperature cause enzyme activity to change as it does at lower temperatures?

C. Why does temperature cause enzyme activity to change as it does at higher temperatures?

10. In the process referred to as feedback inhibition:

A. end-products of a metabolic pathway cycle back to the beginning and serve as substrates.

B. beginning substrates of a metabolic pathway inhibit enzymes further down in the pathway.

C. end-products that accumulate inhibit one or more enzymes earlier in the pathway.

D. enzymes from the end of a metabolic pathway inhibit enzymes earlier in the pathway

11. In red blood cells the enzyme Carbonic Anhydrase catalyzes the following reversible reaction: CO2 + H2O ↔ H2CO3. The H2CO3 produced is the principal form in which CO2 is carried to the lungs through the blood.

In the lungs the enzyme operates in the direction of CO2 production:

H2CO3 → CO2 + H2O

In the peripheral tissues, the enzyme operates in the opposite direction:

CO2 + H2O → H2CO3

A. Which gas is continuously removed from the blood in the lungs? ______Why will this tend to force the enzymatic reaction toward production of CO2?

B. Which gas is continually released into the blood from peripheral tissues? ______Why will this tend to force the reaction toward H2CO3 production?

12. Substrates bind to the ______site of an enzyme, which speeds up the reaction by reducing / increasing (circle) the activation energy List three ways in which the enzyme alters the activation energy.

1.

2.

3.

13. In the diagram of ATP to the right:

A. Label the triphosphate and the two other molecular components of ATP.

B. Label the bond that is broken in the reaction in which ATP is converted to ADP.

C. Label the bond that is broken in the reaction in which ATP is converted to AMP.

14. The enzyme phosphoglucomutase will convert glucose-6-phosphate to fructose-6-phosphate. Suppose that you combined 100 mg of glucose-6-phosphate with the enzyme; would you expect it all to be converted to fructose-6-phosphate? Explain your answer.

15. Using the diagram to the right, draw lines that show the possible ways in which the intermediates or end-products of this pathway could possibly participate in feedback inhibition. Can you find all 6 ways?

16. Alcohol consumption leads to abnormal accumulation of NADH and other metabolic imbalances. As shown above, alcohol is metabolized in the liver by two reactions, first by the enzyme ADH in the cytosol and then by the enzyme ALDH in mitochondria. One treatment of alcoholism is the drug disulfiram, a noncompetitive inhibitor of ALDH. A person on disulfiram who consumes alcohol will experience an accumulation of acetaldehyde, which causes nausea and vomiting, a significant deterrent to further drinking. (For A – D, circle the correct answer)

A. NAD+ is a(n) enzyme/ coenzyme / prosthetic group.

B. In these reaction NAD+ is receiving / donating electrons.

C. In these reactions, ethanol and acetaldehyde are oxidized / reduced .

D. These molecules are undergoing catabolism / anabolism .

E. Circle and name the three functional groups that are being altered by these reactions. Of these functional groups the ______group is the most oxidized and the ______group is the most reduced.

F. Considering that disulfiram is a noncompetitive inhibitor, would you expect it to bind to and block the ALDH catalytic site? Explain.

17. A. Explain how you know that in the reaction shown here, where xxx is converted to zzz, that xxx is more oxidized than zzz?

B. Explain how you know that in the reaction shown here, where aaa is converted to bbb, that the reaction is exogonic (energy releasing)?

How do you know that this reaction does not involve oxidation/reduction?

18. Consider the reaction shown below. For questions A-D circle the correct answers.

A. Aspartate is oxidized / reduced / neither .

B. ATP is oxidized / reduced / neither .

C. NH3 is a cofactor / coenzyme / substrate .

D. The overall reaction is catabolic / anabolic .

E. Draw an energy curve for this reaction.

·  Label the substrates and products;

·  Label the activation energy between two points on the curve.

·  Label the ΔG between two points on the curve.

·  Draw a dotted line to show how the curve would be different in the absence of a catalytic enzyme.

Biol 131 Question bank Energy and Metabolism

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