Chapter 6 pre/post quiz

The ∆G for a particular enzyme-catalyzed reaction is -20 kcal/mol. If the amount of enzyme in the reaction is doubled, what will be the ∆G for the new reaction?

• -20kcal/mol

• -40 kcal/mol

• 0 kcal/mol

• +40 kcal/mol

• +20 kcal/mol

Anabolic pathways share which of the following characteristics?

• They are usually spontaneous chemical reactions that do not require an input of energy

• They are not dependent on enzymes

• They consume energy to synthesize polymers from monomers.

• They release energy as they degrade polymers to monomers.

Which of the following is the most comprehensive definition of metabolism in living organisms?

• Metabolism depends on a constant supply of energy from food.

• Metabolism consists of all the energy transformation reactions in an organism.

• Metabolism refers to the sum of all biochemical pathways involved in synthesis of macromolecules.

• Metabolism manages the increase of entropy in an organism.

ATP hydrolysis in a test tube releases only about half as much energy as ATP hydrolysis in the cell. Which of the following statements is the best explanation for this observation?

• Reactant and product concentrations in the cell are different from the standard conditions used in a test tube.

• Cells maintain higher internal pressure, which speeds up the reaction rate.

• ATP hydrolysis in cells is catalyzed by enzymes, which releases more energy than the uncatalyzed reaction in a test tube.

• ATP hydrolysis in a cell produces different products than ATP hydrolysis in a test tube.

An aminoacyl-tRNA synthetase is the enzyme that catalyzes the attachment of a particular amino acid to its corresponding tRNA. This reaction requires energy from ATP. The enzyme initially binds the amino acid and ATP, but it is unable to bind the tRNA at this point. Which of the following would be a likely next step in the reaction by which the enzyme ultimately binds the tRNA and attaches the amino acid?

• Hydrolysis of ATP phosphorylates the amino acid, which results in a conformational change in the active site that allows the tRNA to bind

• Transfer of the ATP to the tRNA opens the active site, which allows the tRNA to bind.

• Alteration in the conformation of the tRNA allows it to bind to the active site along with the amino acid and ATP.

• Hydrolysis of ATP activates the amino acid, which is released, opening up the active site to allow binding of the tRNA, followed by binding of a new amino acid.

A noncompetitive inhibitor decreases the rate of an enzymatic reaction by

• changing the ∆G for the reaction.

• binding to the active site of the enzyme.

• changing the shape of the enzyme active site.

• decreasing the activation energy required for the reaction.

Based on the first law of thermodynamics, which of the following statements about a living organism is true?

• The entropy of an organism decreases with time as the organism grows in complexity.

• An organism grows by converting energy into organic matter.

• The organism ultimately must obtain all of the necessary energy for life from its environment.

• The energy content of an organism is constant.

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

• 
  exergonic.

• endergonic.

• spontaneous.

• at equilibrium.

Which of the following statements is a logical consequence of the second law of thermodynamics?

• Every chemical reaction must increase the total entropy of the universe.

• Every energy transfer requires activation energy from the environment.

• If the entropy of a system increases, there must be a corresponding decrease in the entropy of the universe.

• f there is an increase in the energy of a system, there must be a corresponding decrease in the energy of the rest of the universe.

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

• noncompetitive inhibitor of the enzyme

• cofactor necessary for enzyme activity.

• allosteric activator of the enzyme.

• competitive inhibitor of the enzyme.

• coenzyme derived from a vitamin.