Chapter 9 Multiple choice questions

Inside an active mitochondrion, most electrons follow which pathway?

citric acid cycle- NADH- electron transport chain- oxygen

When skeletal muscle cells are oxygen-deprived, the heart still pumps. What must the heart muscle cells be able to do?

continue aerobic metabolism when skeletal muscle cannot

Which of the following occurs in the cytosol of a eukaryotic cell?

glycolysis and fermentation

A molecule that is phosphorylated

has an increased chemical potential energy; it is primed to do cellular work

Where are the proteins of the electron transport chain located?

mitochondrial inner membrane

The ATP made during glycolysis is generated by

substrate-level phosphorylation

Starting with one molecule of isocitrate and ending with fumarate, how many ATP molecules can be made through substrate-level phosphorylation (see Figure 9.2)?

1

Substrate-level phosphorylation accounts for approximately what percentage of the ATP formed by the reactions of glycolysis?

100%

For each molecule of glucose that is metabolized by glycolysis and the citric acid cycle (see Figure 9.2), what is the total number of NADH + FADH2 molecules produced?

12

How many oxygen molecules (O2) are required each time a molecule of glucose (C6H12O6) is completely oxidized to carbon dioxide and water via aerobic respiration?

6

In a mitochondrion, if the matrix ATP concentration is high, and the intermembrane space proton concentration is too low to generate sufficient proton-motive force, then

ATP synthase will hydrolyze ATP and pump protons into the intermembrane space

In the absence of oxygen, yeast cells can obtain energy by fermentation, resulting in the production of

ATP, CO2, and ethanol (ethyl alcohol)

Which of the following statements describes the results of this reaction? C6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy

C6H12O6 is oxidized and O2 is reduced

During aerobic respiration, which of the following directly donates electrons to the electron transport chain at the lowest energy level?

FADH2

Why is glycolysis considered to be one of the first metabolic pathways to have evolved?

It does not involve organelles or specialized structures, does not require oxygen, and is present in most organisms.

In liver cells, the inner mitochondrial membranes are about five times the area of the outer mitochondrial membranes. What purpose must this serve?

It increases the surface for oxidative phosphorylation

Why is glycolysis described as having an investment phase and a payoff phase?

It uses stored ATP and then forms a net increase in ATP.

You have a friend who lost 7 kg (about 15 pounds) of fat on a regimen of strict diet and exercise. How did the fat leave her body?

It was released as CO2 and H2O

The free energy for the oxidation of glucose to CO2 and water is -686 kcal/mol and the free energy for the reduction of NAD+ to NADH is +53 kcal/mol. Why are only two molecules of NADH formed during glycolysis when it appears that as many as a dozen could be formed?

Most of the free energy available from the oxidation of glucose remains in pyruvate, one of the products of glycolysis.

Which of the following statements describes NAD+?

NAD+ is reduced to NADH during glycolysis, pyruvate oxidation, and the citric acid cycle

Figure 9.3 shows the electron transport chain. Which of the following is the combination of substances that is initially added to the chain?

NADH, FADH2, and O2

When electrons move closer to a more electronegative atom, what happens?

The more electronegative atom is reduced, and energy is released.

A mutation in yeast makes it unable to convert pyruvate to ethanol. How will this mutation affect these yeast cells?

The mutant yeast will be unable to grow anaerobically.

When electrons flow along the electron transport chains of mitochondria, which of the following changes occurs?

The pH of the matrix increases.

In cellular respiration, the energy for most ATP synthesis is supplied by

a proton gradient across a membrane.

The oxygen consumed during cellular respiration is involved directly in which process or event?

accepting electrons at the end of the electron transport chain

Which of the following intermediary metabolites enters the citric acid cycle and is formed, in part, by the removal of a carbon (CO2) from one molecule of pyruvate?

acetyl CoA

The primary role of oxygen in cellular respiration is to

act as an acceptor for electrons and hydrogen, forming water

The transport of pyruvate into mitochondria depends on the proton-motive force across the inner mitochondrial membrane. How does pyruvate enter the mitochondrion?

active transport

Chemiosmotic ATP synthesis (oxidative phosphorylation) occurs in

all respiring cells, both prokaryotic and eukaryotic, using either oxygen or other electron acceptors.

Which kind of metabolic poison would most directly interfere with glycolysis?

an agent that closely mimics the structure of glucose but is not metabolized

The synthesis of ATP by oxidative phosphorylation, using the energy released by movement of protons across the membrane down their electrochemical gradient, is an example of

an endergonic reaction coupled to an exergonic reaction

What is the term for metabolic pathways that release stored energy by breaking down complex molecules?

catabolic pathways

Most CO2 from catabolism is released during

the citric acid cycle.

In chemiosmosis, what is the most direct source of energy that is used to convert ADP + i to ATP?

energy released from movement of protons through ATP synthase, down their electrochemical gradient

During aerobic respiration, electrons travel downhill in which sequence?

food-NADH- electron transport chain- oxygen

What carbon sources can yeast cells metabolize to make ATP from ADP under anaerobic conditions?

glucose

Even though plants carry on photosynthesis, plant cells still use their mitochondria for oxidation of pyruvate. When and where will this occur?

in all cells all the time

In prokaryotes, the respiratory electron transport chain is located

in the plasma membrane.

Phosphofructokinase is an allosteric enzyme that catalyzes the conversion of fructose 6-phosphate to fructose 1,6-bisphosphate, an early step of glycolysis. In the presence of oxygen, an increase in the amount of ATP in a cell would be expected to

inhibit the enzyme and thus slow the rates of glycolysis and the citric acid cycle

An organism is discovered that thrives both in the presence and absence of oxygen in the air. Curiously, the consumption of sugar increases as oxygen is removed from the organism's environment, even though the organism does not gain much weight. This organism

is a facultative anaerobe.

The molecule that functions as the reducing agent (electron donor) in a redox or oxidation-reduction reaction

loses electrons and loses potential energy.

Carbon dioxide (CO2) is released during which of the following stages of cellular respiration?

oxidation of pyruvate to acetyl CoA and the citric acid cycle

One function of both alcohol fermentation and lactic acid fermentation is to

oxidize NADH to NAD+

When a glucose molecule loses a hydrogen atom as the result of an oxidation-reduction reaction, the molecule becomes

oxidized.

When a molecule of NAD+ (nicotinamide adenine dinucleotide) gains a hydrogen atom (not a proton), the molecule becomes

reduced

In alcohol fermentation, NAD+ is regenerated from NADH by

reduction of acetaldehyde to ethanol (ethyl alcohol)

An electron loses potential energy when it

shifts to a more electronegative atom

What is proton-motive force?

the force provided by a transmembrane hydrogen ion gradient

The direct energy source that drives ATP synthesis during respiratory oxidative phosphorylation in eukaryotic cells is

the proton-motive force across the inner mitochondrial membrane

In glycolysis, for each molecule of glucose oxidized to pyruvate

two molecules of ATP are used and four molecules of ATP are produced