Which of the following are effects produced by an enzyme on the reaction S lefta

Question

Which of the following are effects produced by an enzyme on the reaction S leftarrow rightarrow P with forward rate constant k_1 and reverse reaction rate constant k_2? a) The reaction equilibrium is shifted away from the products: b) The formation of transition state is promoted c) Delta G increases d) activation energy. Delta G* decreases e) The rate constant for the reverse reaction increases f) The activation energy increases What would be the strongest interaction between Asp on the substrate and Lys on the enzyme active site at pH = 7? (choose one best answer) a) ionic interaction b) hydrophobic c) H-bonding d) disulfide formation An enzyme belonging to which of the six classes of enzymes would be expected to catalyze the following reaction? And what cofactor would be expected to be needed? (choose one best answer). a. oxidoreductase and FAD b) oxidoreductase and NAD^+ c. hydrolase and Mg^2+ d. transferase and pyridoxal phosphate. e. isomerase and no cofactor n

Explanation / Answer

Ans. 1. Enzyme acts as biocatalyst. So, like other catalysts, enzyme also decreases the activation energy of the reaction (D). Lowering of activation energy favors the formation of transition state complex (B).

The rate constant for both the forward and backward reactions are increased in same proportion (E). The simultaneous proportionate increment in reaction rates of both forward and backward reaction causes the equilibrium constant remaining unaffected.

Thus, correct options are- B, D, E.

Option C. dG0 = -RT ln K. Since enzyme does not affect the value of equilibrium constant K, dG0 also remains unaffected.

Option A: Equilibrium remains unaffected.

Option F. Activation energy decreases.

#2. Correct option. A. Both Aspartic acid (negatively charged side chain) and Lysine (positively charged side chain) strongly interacts through ionic interactions because of having oppositely charged side chains.

Hydrophobic interaction occurs between non-polar side chains of hydrophobic amino acids. Since these amino acids’ side chain are polar and charged, hydrophobic interaction is insignificant.

Ionic interactions have more profound effects than H-bonds in catalysis.

Disulfide bond forms between two cysteine residues, but not between any other residues.

#3. Correct option. A

The reaction, conversion of succinate into fumarate is catalyzed by succinate dehydrogenase- class oxidoreductase, requires FAD as cofactor.

#4. C. Isomerase

Note the change in structure of the reactant and the product. There is shifting of a double bond within the molecule.

The enzymes catalyzing intramolecular (within the molecule) geometric or structural changes are classified as ‘Isomerases’.

#5. B. Transferase

Note that a phosphate group is being transferred to the substrate sugar. The enzyme belongs to class transferase.

The enzymes catalyzing the transfer of a function group from donor to acceptor molecule belong to ‘Transferases’. Generally, the functional group on donor is considered (formally) to be exchanged with a hydrogen on the acceptor molecule.

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