Chapter 8

In cells, what is usually the immediate source of energy for an endergonic reaction?

ATP

How does an enzyme increase the rate of the chemical reaction it catalyzes?

An enzyme reduces the free energy of activation (EA) of the reaction it catalyzes.

Which of the following is true of enzymes?

Enzymes increase the rate of chemical reaction by lowering activation energy barriers.

What is the fate of the phosphate group that is removed when ATP is converted to ADP?

It is acquired by a reactant in an endergonic reaction.

Which of the following statements is most likely to be true in the case of the feedback-regulated enzymatic pathway shown?

P4 binds E1 and deactivates it.

According to the induced fit hypothesis of enzyme catalysis, which of the following is correct?

The binding of the substrate changes the shape of the enzyme's active site.

Which of the following is true for all exergonic reactions?

The reaction proceeds with a net release of free energy.

Reactants capable of interacting to form products in a chemical reaction must first overcome a thermodynamic barrier known as the reaction's

activation energy

A series of enzymes catalyze the reaction X→Y→Z→A. Product A binds to the enzyme that converts X to Y at a position remote from its active site. This binding decreases the activity of the enzyme. Substance A functions as

an allosteric inhibitor.

Sucrose is a disaccharide, composed of the monosaccharides glucose and fructose. The hydrolysis of sucrose by the enzyme sucrase results in

breaking the bond between glucose and fructose and forming new bonds from the atoms of water.

Which term most precisely describes the cellular process of breaking down large molecules into smaller ones?

catabolism

Zinc, an essential trace element for most organisms, is present in the active site of the enzyme carboxypeptidase. The zinc most likely functions as a(n)

cofactor necessary for enzyme activity.

A chemical reaction that has a positive ΔG is correctly described as

endergonic

The reaction ADP + P --> ATP is a(n) _____ reaction.

endergonic

A(n) _____ reaction occurs spontaneously.

exergonic

The energy for an endergonic reaction comes from a(n) _____ reaction.

exergonic

The reaction A --> B + C + heat is released in a(n) _____ reaction.

exergonic

Some of the drugs used to treat HIV patients are competitive inhibitors of the HIV reverse transcriptase enzyme. Unfortunately, the high mutation rate of HIV means that the virus rapidly acquires mutations with amino acid changes that make them resistant to these competitive inhibitors. Where in the reverse transcriptase enzyme would such amino acid changes most likely occur in drug-resistant viruses?

in or near the active site

The active site of an enzyme is the region that

is involved in the catalytic reaction of the enzyme.

What is energy coupling?

the use of energy released from an exergonic reaction to drive an endergonic reaction