Chapter 13 Smartwork

How do enzymes maximize the energy harvested from the oxidation of food molecules?

a. They allow a larger amount of energy to be released from food molecules such as glucose.

b. They allow what would otherwise be an energetically unfavorable oxidation reaction to occur.

c. They guarantee that each reaction involved in the oxidation of food molecules proceeds in just one direction.

d. They allow the stepwise oxidation of food molecules, which releases energy in small amounts.

d. They allow the stepwise oxidation of food molecules, which releases energy in small amounts.

Enzymes allow cells to carry out the oxidation of sugars in a tightly controlled stepwise series of reactions. These reactions pay out energy in small packets to activated carriers, which allows cells to capture much of the energy released by the oxidative breakdown of glucose in the high-energy bonds of ATP and other activated carriers.

Which of the following generates the largest number of ATP molecules?

a. glycolysis

b. citric acid cycle

c. gluconeogenesis

d. electron-transport chain

d. electron-transport chain

The electron-transport chain in the inner mitochondrial membrane generates large amounts of ATP from electrons donated by the active carriers produced during glycolysis and the citric acid cycle.

In step 6 of glycolysis, glyceraldehyde 3-phosphate, which has one phosphate group, is converted into 1,3-bisphosphoglycerate, which has two. Where does the extra phosphate group come from?

a. ATP

b. NADPH

c. fructose 1,6-bisphosphate

d. a free phosphate molecule

d. a free phosphate molecule

This is the only substrate-level phosphorylation in glycolysis that creates a high-energy phosphate linkage directly from a free phosphate.

In eukaryotic cells, why must metabolism be tightly regulated?

a. The substrates involved in metabolic reactions are chemically reactive.

b. The substrates involved in metabolic reactions can be used by a number of different enzymes.

c. Anabolic and catabolic pathways must compete for scarce resources.

d. All metabolic reactions require energy.

b. The substrates involved in metabolic reactions can be used by a number of different enzymes.

Pyruvate alone is a substrate for half a dozen or more different enzymes, each of which modifies it chemically in a different way. Pyruvate can be used to produce acetyl CoA, can be converted to lactate during fermentation, or can be used to make oxaloacetate or the amino acid alanine. All these pathways compete for pyruvate molecules, and similar competitions for thousands of other small molecules go on in cells all the time. Thus, metabolism must be tightly regulated so that these competing reactions can be coordinated and controlled.