The activity of an enzyme was examined in the laboratory as it catalyzed the for

Question

The activity of an enzyme was examined in the laboratory as it catalyzed the formation of the product B, from the substrate A. This reaction was carried out in an aqueous solution consisting of water and copper sulfate at a pH of 7. While attempting to repeat the experiment, a biochemist uses a solution of pure distilled water (pH = 7) and observes that the rate of formation of B has decreased dramatically. Which is the most likely possible explanation for this result?

Enzyme-substrate affinities are influenced by non-covalent intermolecular interactions such as hydrogen bonding, ionic interactions, hydrophobic interactions and van der Waals forces between the two molecules. The dissociation constant (abbreviated KD; has molar (M) units) is commonly used to describe the affinity between an enzyme and its substrate. The smaller the dissociation constant, the higher the affinity between enzyme and substrate (i.e., the more tightly bound the substrate is).

A kinase is an enzyme that catalyzes the transfer of phosphate groups to specific substrates. Protein kinases often have multiple substrates. A theoretical kinase can phosphorylate five different substrates (A-E). The dissociation constants for these substrates and the kinase are listed below. Which substrate will produce the greatest concentration of enzyme–substrate complex?

Substrate E, KD = 107 M.

Substrate D, KD = 104 M.

Substrate C, KD = 100 M.

Substrate A, KD = 10–7 M.

Substrate B, KD = 10–4 M.

Fumarase is the enzyme that catalyzes the following reaction between fumarate and water to produce malate in cells. Which statement can be used as evidence that orientation of reactant molecules is part of the function of fumarase as a catalyst?

Fumarase does not use a coenzyme but requires one Fe2+ ion at its active site.

The enzyme alcohol dehydrogenase was purified from yeast cells. It was then dialyzed against a buffer solution, which means that it was placed inside a bag consisting of a semipermeable membrane that allowed small molecules and ions to pass through, but not the enzyme. The enzyme was removed from the dialysis bag, incubated with the small compound N-ethylmaleimide, and then dialyzed a second time. At each step, the enzyme’s catalytic activity was measured and expressed as a percentage of its original activity shown in the table below. Which statement expresses a valid conclusion that can be made based on these results?

A branched metabolic pathway involving various metabolites (indicated by letters) is shown below. The enzymes catalyzing the steps in this pathway are indicated with numbers. Based on the pathway shown, which of the following would most likely be expected?

C6H12O6 + 6 O2  ?  6 CO2 + 6 H2O.

C2H5OH + NAD+ ? C2H4O + NADH + H+.

2 C4H10 + 13 O2 ? 8 CO2 + 10 H2O.

NADH + H+ + ½ O2 ? NAD+ + H2O.

ADP + Pi ? ATP + H2O.

Which half-reactions represent a change from more stored free energy to less stored free energy?

AH ? A and NADH ? NAD+.

AH ? A and NAD+ ? NADH.

B ? BH and NADH ? NAD+.

AH ? A and B ? BH.

B ? BH and NAD+ ? NADH.

The figure below shows a series of coupled reactions. Which terms belong in the numbered boxes?

1.

The activity of an enzyme was examined in the laboratory as it catalyzed the formation of the product B, from the substrate A. This reaction was carried out in an aqueous solution consisting of water and copper sulfate at a pH of 7. While attempting to repeat the experiment, a biochemist uses a solution of pure distilled water (pH = 7) and observes that the rate of formation of B has decreased dramatically. Which is the most likely possible explanation for this result?

The enzyme’s optimal activity is not at pH 7. Sulfate ions inhibit binding of A to the enzyme’s active site. The enzyme needs copper ions to act as cofactors for optimal enzyme activity. The enzyme needs the presence of a coenzyme to function. B is unstable and cannot be measured. 2.

Enzyme-substrate affinities are influenced by non-covalent intermolecular interactions such as hydrogen bonding, ionic interactions, hydrophobic interactions and van der Waals forces between the two molecules. The dissociation constant (abbreviated KD; has molar (M) units) is commonly used to describe the affinity between an enzyme and its substrate. The smaller the dissociation constant, the higher the affinity between enzyme and substrate (i.e., the more tightly bound the substrate is).

A kinase is an enzyme that catalyzes the transfer of phosphate groups to specific substrates. Protein kinases often have multiple substrates. A theoretical kinase can phosphorylate five different substrates (A-E). The dissociation constants for these substrates and the kinase are listed below. Which substrate will produce the greatest concentration of enzyme–substrate complex?

Substrate E, KD = 107 M.

Substrate D, KD = 104 M.

Substrate C, KD = 100 M.

Substrate A, KD = 10–7 M.

Substrate B, KD = 10–4 M.

3.

Fumarase is the enzyme that catalyzes the following reaction between fumarate and water to produce malate in cells. Which statement can be used as evidence that orientation of reactant molecules is part of the function of fumarase as a catalyst?

The active site of fumarase contains a histidine and a lysine that function as an acid and a base, respectively, during catalysis.

Fumarase does not use a coenzyme but requires one Fe2+ ion at its active site.

Fumarase binds one fumarate molecule and one water molecule the same way for every reaction. Mutation of the active site lysine to other amino acids obliterates or severely reduces activity in fumarase. Fumarase catalyzes both the forward and reverse reactions between fumarate and malate. 4.

The enzyme alcohol dehydrogenase was purified from yeast cells. It was then dialyzed against a buffer solution, which means that it was placed inside a bag consisting of a semipermeable membrane that allowed small molecules and ions to pass through, but not the enzyme. The enzyme was removed from the dialysis bag, incubated with the small compound N-ethylmaleimide, and then dialyzed a second time. At each step, the enzyme’s catalytic activity was measured and expressed as a percentage of its original activity shown in the table below. Which statement expresses a valid conclusion that can be made based on these results?

N-ethylmaleimide is a reversible inhibitor of alcohol dehydrogenase. N-ethylmaleimide is a noncompetitive inhibitor of alcohol dehydrogenase. N-ethylmaleimide is an irreversible inhibitor of alcohol dehydrogenase. N-ethylmaleimide is a competitive inhibitor of alcohol dehydrogenase. N-ethylmaleimide is an activator of alcohol dehydrogenase. 5.

A branched metabolic pathway involving various metabolites (indicated by letters) is shown below. The enzymes catalyzing the steps in this pathway are indicated with numbers. Based on the pathway shown, which of the following would most likely be expected?

Enzyme 7 is allosterically inhibited by metabolite K. Metabolite D functions as a competitive inhibitor of enzyme 1. Enzyme 3 is allosterically inhibited by metabolite G. Enzyme 10 is allosterically activated by metabolite E. Metabolite G functions as a competitive inhibitor of enzyme 4. 6. Which reaction is not an example of a redox reaction?

C6H12O6 + 6 O2  ?  6 CO2 + 6 H2O.

C2H5OH + NAD+ ? C2H4O + NADH + H+.

2 C4H10 + 13 O2 ? 8 CO2 + 10 H2O.

NADH + H+ + ½ O2 ? NAD+ + H2O.

ADP + Pi ? ATP + H2O.

7. What amount of free energy is released by the oxidation of 2 moles of NADH? 7.3 kcal. 21.9 kcal. 104.8 kcal. 52.4 kcal. 14.6 kcal. 8.

Which half-reactions represent a change from more stored free energy to less stored free energy?

AH ? A and NADH ? NAD+.

AH ? A and NAD+ ? NADH.

B ? BH and NADH ? NAD+.

AH ? A and B ? BH.

B ? BH and NAD+ ? NADH.

9.

The figure below shows a series of coupled reactions. Which terms belong in the numbered boxes?

1 = oxidation; 2 = reduction; 3 = oxidation; 4 = reduction. 1 = reduction; 2 = oxidation; 3 = reduction; 4 = oxidation. 1 = oxidation; 2 = reduction; 3 = reduction; 4 = oxidation. 1 = oxidation; 2 = oxidation; 3 = reduction; 4 = reduction. 1 = reduction; 2 = reduction; 3 = oxidation; 4 = oxidation. 10. 14.Catabolic interconversion is a metabolic pathway in which _____. small molecules are broken down into CO2 and water molecules and requires energy. a citric acid intermediate is a starting point. a large molecule is broken down into its constituent molecules and releases energy. many small molecules are combined into larger molecules and a pathway that requires energy. large molecules are built up into even larger molecules and a pathway that requires energy.

Explanation / Answer

1.
Correct option:

Explanation: Copper ions in aqueous solution acts as a cofactor for the enzyme for the formation of product B from substrate A. Without the cofactor the conversion of substrate A to product B reduces drastically.

2.
Correct option:

Explanation: Substrate A has the smallest KD value among the substrates. Hence it will have higher affinity.

3.
Correct option:

4.
Correct option:

Explanation: Since N-ethylmaleimide is an irreversible inhibitor of alcohol dehydrogenase the enzymatic activity is reduced to zero.

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