Ch 7: Cellular Respiration and Fermentation

Question 1

Which of the following statements about the electron transport chain is true?

a. ) The electron transport chain is the first step in cellular respiration.
b. ) NADH and FADH2 donate their electrons to the chain.
c. ) Water is the last electron acceptor.
d. ) Electrons gain energy as they move down the chain.

Answer 1

b.) NADH and FADH2 donate their electrons to the chain.

Question 2

Which stage of glucose metabolism produces the most ATP?

a. ) Electron transport and chemiosmosis
b. ) Glycolysis
c. ) Fermentation of pyruvate to lactate
d. ) Krebs cycle

Answer 2

a.) Electron transport and chemiosmosis

Question 3

Cellular respiration begins with glycolysis in the cytosol. Pyruvate, the product of glycolysis, then enters the mitochondrial matrix, crossing both the outer and inner membranes. Both acetyl CoA formation and the citric acid cycle take place in the ______.

Answer 3

matrix

Question 4

In glycolysis, the six-carbon sugar glucose is converted to two molecules of ________ (three carbons each), with the net production of _ ___ and _ ____ per glucose molecule. There is NO O2 uptake or CO2 release in glycolysis.

Answer 4

pyruvate
2 ATP
2 NADH

Question 5

In acetyl CoA formation, pyruvate (a product of glycolysis) is oxidized to ______ ___, with the reduction of NAD⁺ to NADH and the release of one molecule of ___.

Answer 5

acetyl CoA

CO₂

Question 6

In the citric acid cycle, the two carbons from the acetyl group of acetyl CoA are oxidized to two molecules of ___, while several molecules of ____ are reduced to NADH and one molecule of FAD is reduced to ____. In addition, one molecule of ATP is produced.

Answer 6

CO₂

NAD⁺

FADH₂

Question 7

The NADH and FADH2 produced during the first three stages release their electrons to the electron transport chain of oxidative phosphorylation at the _____ _____________ membrane. The inner membrane provides the barrier that creates an __ gradient during electron transport, which is used for ATP synthesis.

Answer 7

inner mitochondrial
H+

Question 8

In oxidative phosphorylation, the NADH and FADH₂ produced by the first three stages of cellular respiration are oxidized in the electron transport chain, reducing O₂ to water and recycling NAD⁺ and FAD back to the first three stages of cellular respiration. The electron transport reactions supply the energy to drive most of a cell’s ATP production.

Answer 8

***

Question 9

Cellular respiration begins with glycolysis in the cytosol. Pyruvate, the product of glycolysis, then enters the mitochondrial matrix, crossing both the outer and inner membranes. Both acetyl CoA formation and the citric acid cycle take place in the matrix. The NADH and FADH₂ produced during the first three stages release their electrons to the electron transport chain of oxidative phosphorylation at the inner mitochondrial membrane. The inner membrane provides the barrier that creates an H⁺ gradient during electron transport, which is used for ATP synthesis.

Answer 9

***

Question 10

The main coupling among the stages of cellular respiration is accomplished by NAD⁺ and NADH. In the first three stages, NAD⁺ accepts electrons from the oxidation of glucose, pyruvate, and acetyl CoA. The NADH produced in these redox reactions then gets oxidized during oxidative phosphorylation, regenerating the NAD⁺ needed for the earlier stages.

Answer 10

***

Question 11

Under anaerobic conditions (a lack of oxygen), the conversion of pyruvate to acetyl CoA stops. What is the correct explanation for this observation?

Answer 11

NAD⁺ couples oxidative phosphorylation to acetyl CoA formation. The NAD⁺ needed to oxidize pyruvate to acetyl CoA is produced during electron transport. Without O₂, electron transport stops, and the oxidation of pyruvate to acetyl CoA also stops because of the lack of NAD⁺.

Question 12

Suppose that a cell’s demand for ATP suddenly exceeds its supply of ATP from cellular respiration.

How would this increased demand lead to an increased rate of ATP production?

Answer 12

ATP levels would fall at first, decreasing the inhibition of PFK and increasing the rate of ATP production.

Question 13

During strenuous exercise, anaerobic conditions can result if the cardiovascular system cannot supply oxygen fast enough to meet the demands of muscle cells. Assume that a muscle cell’s demand for ATP under anaerobic conditions remains the same as it was under aerobic conditions.

What would happen to the cell’s rate of glucose utilization?

Answer 13

Glucose utilization would increase a lot.

Question 14

ATP made during fermentation comes from glycolysis, which produces a net of only 2 ATP per glucose molecule. In contrast, aerobic cellular respiration produces about 30 ATP per glucose molecule. To meet the same ATP demand under anaerobic conditions as under aerobic conditions, a cell’s rate of glycolysis and glucose utilization must increase about 15-fold.

Answer 14

***

Question 15

A negative ΔG indicates that the products of the chemical process store ____ ______ than the reactants and that the reaction can happen spontaneously—in other words, without an input of energy.

Answer 15

less energy

Question 16

Not all redox reactions involve the complete transfer of electrons from one substance to another; some change the degree of ________ _______ in covalent bonds.

Answer 16

electron sharing

Question 17

An electron loses ________ ______ when it shifts from a less electronegative atom toward a more electronegative one, just as a ball loses potential energy when it rolls downhill.

Answer 17

potential energy

Question 18

What are the reactants in the process of cellular respiration?

Answer 18

glucose and oxygen

Question 19

What are the products of cellular respiration?

Answer 19

carbon dioxide, water, and energy (ATP + heat)

Question 20

In general, organic molecules that have an abundance of hydrogen are excellent fuels because their bonds are a source of “hilltop” electrons, whose energy may be released as these electrons “fall” down an energy gradient during their transfer to oxygen. The summary equation for respiration indicates that hydrogen is transferred from glucose to oxygen. But the important point, not visible in the summary equation, is that the energy state of the electron changes as hydrogen (with its electron) is transferred to oxygen. In respiration, the oxidation of glucose transfers electrons to a _____ _____ _____, liberating energy that becomes available for ATP synthesis. So, in general, we see fuels with multiple C−H bonds oxidized into products with multiple ___ bonds.

Answer 20

lower energy state

C−O

Question 21

As is often the case in oxidation reactions, each electron travels with a proton—thus, as a hydrogen atom. The hydrogen atoms are not transferred directly to oxygen, but instead are usually passed first to an electron carrier, a ________ called nicotinamide adenine dinucleotide, a derivative of the vitamin ______.

Answer 21

coenzyme

niacin

Question 22

This coenzyme is well suited as an electron carrier because it can cycle easily between its oxidized form, NAD+, and its reduced form, NADH. As an electron acceptor, NAD+ functions as an __________ _____ during respiration.

Answer 22

oxidizing agent

Question 23

How does NAD+ trap electrons from glucose and other organic molecules in food? Enzymes called ______________ remove a pair of hydrogen atoms (2 electrons and 2 protons) from the substrate (glucose, in the preceding example), thereby oxidizing it. The enzyme delivers _ ______ along with 1 ______ to its coenzyme, NAD+, forming NADH (Figure 7.4). The other proton is released as a hydrogen ion (H+) into the surrounding solution:

Answer 23

dehydrogenases

2 electrons

proton

Question 24

The full name for NAD⁺, nicotinamide adenine dinucleotide, describes its structure. The molecule consists of two nucleotides joined together at their phosphate groups. Nicotinamide is a ___________ ____, although not one that is present in DNA or RNA. NAD+ is the most _________ electron acceptor in cellular respiration and functions in several of the redox steps during the breakdown of glucose.

Answer 24

nitrogenous base

versatile

Question 25

An electron transport chain consists of a number of molecules, mostly proteins, built into the inner membrane of the mitochondria of eukaryotic cells and the plasma membrane of aerobically respiring prokaryotes. Electrons removed from glucose are shuttled by NADH to the “top,” higher-energy end of the chain. At the “bottom,” lower-energy end, O₂ captures these electrons along with hydrogen nuclei (H+), forming _____. (Anaerobically respiring prokaryotes have an ________ ________ at the end of the chain that is different from O2.)

Answer 25

water

electron acceptor

Question 26

In the electron transport chain, each “downhill” carrier is more ______________ than, and thus capable of oxidizing, its “uphill” neighbor, with oxygen at the bottom of the chain. Therefore, the electrons transferred from glucose to NAD+, reducing it to NADH, fall down an energy gradient in the electron transport chain to a far more stable location in the electronegative oxygen atom. Put another way, oxygen pulls electrons down the chain in an energy-yielding tumble analogous to gravity pulling objects downhill.

Answer 26

electronegative

Question 27

In eukaryotic cells, the inner membrane of the mitochondrion is the site of electron transport and another process called chemiosmosis, together making up oxidative phosphorylation. (In prokaryotes, these processes take place in the ______ ________.)

Answer 27

plasma membrane

Question 28

Oxidative phosphorylation accounts for almost __% of the ATP generated by respiration. A smaller amount of ATP is formed directly in a few reactions of glycolysis and the citric acid cycle by a mechanism called ________ _____ _____________. This mode of ATP synthesis occurs when an enzyme transfers a phosphate group from a substrate molecule to ADP, rather than adding an inorganic phosphate to ADP as in oxidative phosphorylation. “Substrate molecule” here refers to an organic molecule generated as an intermediate during the catabolism of glucose.

Answer 28

90

substrate-level phosphorylation

Question 29

For each molecule of glucose degraded to carbon dioxide and water by respiration, the cell makes up to about __ molecules of ATP, each with 7.3 kcal/mol of free energy. Respiration cashes in the large denomination of energy banked in a single molecule of glucose (686 kcal/mol) for the small change of many molecules of ATP, which is more practical for the cell to spend on its work.

Answer 29

32

Question 30

The net energy yield from glycolysis per glucose molecule is…

Answer 30

….2 ATP, plus 2 NADH, plus 2 pyruvate, plus 2 H2O.

Question 31

The net energy yield PER GLUCOSE MOLECULE from the citric acid cycle (Krebs cycle) is:

Answer 31

2 ATP

6 NADH

2 FADH₂

(these numbers represent 2 full turns of the citric acid cycle – since each molecule of glucose produces 2 pyruvate molecules, which in turn produce 2 acetyl groups)

Question 32

The first 4 ATP molecules produced by cellular respiration are all done by…

Answer 32

….substrate level phosphorylation.

Question 33

The proximate (immediate) source of energy for oxidative phosphorylation is _____.

Answer 33

kinetic energy that is released as hydrogen ions diffuse down their concentration gradient

Question 34

In muscle cells, fermentation produces _____.

Answer 34

lactate and NAD+

(it doesn’t produce ATP, but it does provide glycolysis with NAD+ which it needs to produce 2 ATP)

Question 35

In fermentation _____ is reduced and _____ is oxidized.

Answer 35

pyruvate

NADH

Question 36

What is the primary role of oxygen in cellular respiration?

Answer 36

to serve as an acceptor for electrons and protons, forming water

Question 37

The basic function of fermentation is…

Answer 37

…the regeneration of NAD⁺, which allows continued ATP production by glycolysis.

Question 38

Which catabolic processes may have been used by cells on ancient Earth before free oxygen became available?

a. ) only glycolysis and fermentation
b. ) only glycolysis and pyruvate oxidation
c. ) only glycolysis and the citric acid cycle
d. ) glycolysis, pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation, using an electron acceptor other than oxygen
e. ) only oxidative phosphorylation, using an electron acceptor other than oxygen

Answer 38

d.) glycolysis, pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation, using an electron acceptor other than oxygen

Question 39

A mutation in yeast knocks out the ability of cells to convert pyruvate to ethanol. How might this mutation affect these yeast cells?

Answer 39

The mutant yeast will be unable to grow anaerobically.

Question 40

Oxidative phosphorylation is made up of both the ______ ________ _____ AND ____________.

Answer 40

electron transport chain

chemiosmosis

Question 41

The electron transport chain requires “energy”, but does not actually utilize ATP, or produce ATP. Where (what phase) is the ATP produced?

Answer 41

in chemiosmosis

Question 42

Is energy required for the hydrogen ions to move down their concentration gradient (from the intermembrane space into the matrix)?

Answer 42

no, this is passive transport (??)

Question 43

After FADH₂ and NADH “drop off” their electrons, they become oxidized to FAD+ and NAD+, and return to “help” in earlier phases of cellular respiration.

Question 44

In general, the hydrolysis of ATP drives cellular work by _________.

a. changing to ADP and phosphate
b. releasing heat
c. lowering the free energy of the reaction
d. acting as a catalyst
e. releasing free energy that can be coupled to other reactions

Answer 44

e. releasing free energy that can be coupled to other reactions

Question 45

Which is a correct description of the events of cellular respiration and the sequence of events in cellular respiration?

a. glycolysis; oxidative phosphorylation; citric acid cycle; oxidation of pyruvate
b. oxidation of glucose to pyruvate; reduction of pyruvate; citric acid cycle; oxidative phosphorylation
c. glycolysis; reduction of pyruvate; citric acid cycle; oxidative phosphorylation
d. oxidation of pyruvate; citric acid cycle; oxidation of glucose to pyruvate; oxidative phosphorylation
e. oxidation of glucose to pyruvate; oxidation of pyruvate; oxidation of acetyl-CoA; oxidative phosphorylation

Answer 45

e. oxidation of glucose to pyruvate; oxidation of pyruvate; oxidation of acetyl-CoA; oxidative phosphorylation