Enzymes

Which of the following is TRUE regarding cofactors?

• Coenzymes are often separate from the enzyme and do not need recharged.

• Metal ions must be covalently attached to function as a cofactor.

• Cofactor is a broad term used for all enzyme "helpers".

• Prosthetic groups can dissociate readily and be regenerated for use in another enzyme.

• An apoenzyme implies that a cofactor is present.

Proton transfer from an acid, lowering the free energy of a reaction’s transition state, is characteristic of

• electrostatic catalysis.

• nucleophilic catalysis.

• general base catalysis.

• general acid catalysis.

• concerted acid-base catalysis.

Which of the following processes would yield and increase in rate?

• the proximity of the reacting groups

• the rotational motions of the substrates and catalytic groups

• the orientations of the substrates and catalytic groups

• all of the above

• none of the above

Enzyme X catalyzes the addition of a hydroxyl group to substrate Y. In the process a metal cofactor is reduced and then reoxidized. What class of enzyme is X?

• oxidoreductase

• ligase

• hydrolase

• isomerase

• lyase

The transition state of an enzyme and substrate reaction

• must always bind the enzyme active site with lower energy than the products.

• is stabilized by enhancing the reverse reaction of E + S→ES.

• is composed of true covalent bonds which decrease its energy.

• is stabilized due to the specificity of the active site for the substrate.

• is stabilized by decreasing the effective concentration.

Research scientists are trying to clone a gene. In order to accomplish this task they join two pieces of DNA. Which class of the enzymes below might accomplish this task?

• oxidoredutase

• ligase

• hydrolase

• isomerase

• lyase

The enzyme pictured above is shown in two configurations, A (open) and B (closed). Upon binding substrate in the active site, the enzyme converts the structure shown in B. Which of the following is true based on the given information?

• The enzyme requires a high concentration of substrate to function.

• This example exemplifies the “lock-and-key” model.

• This enzyme must require ATP.

• This example exemplifies the of “induced fit” model.

• None of these are true.

The ability for an enzyme to change its shape upon substrate binding represents the concept of

• lock and key.

• induced fit.

• proximity and orientation effects.

• covalent catalysis.

• none of the above

The highest point in a reaction coordinate diagram represents

• an intermediate of the reaction pathway.

• the reactants in an exergonic reaction.

• the products in an endergonic reaction.

• the transition state.

• the overall delta G for the reaction.

How does a catalyst increase the rate of a reaction?

• It makes the reaction more exergonic.

• It increases the temperature of the reaction.

• It allows reacting molecules to more easily form the transition state.

• It causes a localized increase in the concentration of the reactants.

• none of the above