Question 1

Which statement best describes the role of enzymes in biochemical reactions?

Accepted Answer

Enzymes lower the activation energy ($$\Delta G$$^{\ddagger}$$) without altering the overall free energy change ($$\Delta G$$) of the reaction.

Question 2

Which of the following best explains why enzymes are highly specific catalysts?

Accepted Answer

Enzymes have active sites with a unique three-dimensional shape and arrangement of atoms that bind only specific substrates.

Question 3

A reaction has a standard free energy change ($$\Delta G$$^{\circ}$$) of -7.53$ kJ/mol. If the concentrations of reactants and products are not at standard conditions, which equation would you use to calculate the actual free energy change ($$\Delta G$$)?

Accepted Answer

$$\Delta G = \Delta G$$^{\circ}$$ + RT \ln \left( \frac{[C][D]}{[A][B]} \right)$$

Question 4

Which of the following statements about cofactors is TRUE?

Accepted Answer

Cofactors can be either small organic molecules (coenzymes) or inorganic ions (metals).

Question 5

Which enzyme class catalyzes the transfer of functional groups from one molecule to another?

Accepted Answer

Transferases

Question 6

The induced fit model of enzyme-substrate binding proposes that:

Accepted Answer

The enzyme changes shape upon substrate binding, forming a complementary active site only after binding.

Question 7

Which of the following best describes the transition state in an enzyme-catalyzed reaction?

Accepted Answer

It is a fleeting molecular structure with the highest free energy along the reaction pathway.

Question 8

Which of the following is a function of proteases?

Accepted Answer

Catalyze the hydrolysis of peptide bonds using water.

Question 9

A potent inhibitor of an enzyme is found to structurally resemble the transition state of the enzyme's catalyzed reaction. This inhibitor is best described as:

Accepted Answer

A transition-state analog (TSA)

Question 10

Which of the following statements about Gibbs free energy ($$\Delta G) is $$correct?

Accepted Answer

$$\Delta G$$ determines whether a reaction can occur spontaneously.

Question 11

An enzyme catalyzes a reaction with a rate enhancement of $$1.4 	imes 10$$^{17}$$ compared to the uncatalyzed rate. What is the most likely reason for this dramatic increase?

Accepted Answer

The enzyme lowers the activation energy ($$\Delta G$$^{\ddagger}$$) required for the reaction.

Question 12

Which of the following is a common feature of enzyme active sites?

Accepted Answer

Active sites are three-dimensional clefts or crevices formed by amino acids from different parts of the sequence.

Question 13

Which equation relates the equilibrium constant ($$K_{eq}) to $$the standard free energy change ($$\Delta G$$^{\circ}$$)?

Accepted Answer

$$K_{eq} = e$$^{-\Delta G^{\circ}$$/RT}$$

Question 14

A cell is performing glycolysis and the concentrations of the following are measured: Fructose 1,6-bisphosphate = $$5.1 	imes 10$$^{-4}$$ M, Dihydroxyacetone phosphate = 3.4$$ 	imes $$10^{-4} M$$, Glyceraldehyde 3-phosphate = $$9.6 	imes 10$$^{-5}$$ M. The standard free energy change ($$\Delta $$G^{\circ}) $$for the reaction is $$+23.8 kJ/$$mol. Which formula would you use to calculate the actual $$\Delta G$$ under these conditions?

Accepted Answer

$$\Delta G = \Delta G$$^{\circ}$$ + RT \ln \left( \frac{[DHAP][G3P]}{[FBP]} \right)$$

Question 15

Which of the following is NOT a type of enzyme specificity?

Accepted Answer

Specificity for the temperature at which the enzyme operates.

Question 16

Which statement about the effect of enzymes on reaction equilibrium is correct?

Accepted Answer

Enzymes do not affect the equilibrium constant ($$K_{eq}$$); they only increase the rate at which equilibrium is reached.

Question 17

Which of the following is a correct description of a coenzyme?

Accepted Answer

A coenzyme is a small organic molecule, often vitamin-derived, that assists in enzyme catalysis.

Question 18

Which of the following best describes the binding energy in enzyme catalysis?

Accepted Answer

It is the energy released by weak interactions between enzyme and substrate, maximized when the substrate is in the transition state.

Question 19

Which of the following is TRUE regarding the role of water in enzyme active sites?

Accepted Answer

Water is usually excluded unless it is a reactant; the active site often has a nonpolar microenvironment.

Enzyme Catalysis, Cofactors, and Thermodynamics in Biochemistry

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