Chapter 8 & 9 (Questions) Flashcards Preview

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Flashcards in Chapter 8 & 9 (Questions) Deck (370):
1

The process of cellular respiration, which converts simple sugars such as glucose into CO2 and water, is an example of _____.

a catabolic pathway

2

Cellular respiration is a

catabolic pathway

3

Energy is observed in two basic forms: potential and kinetic. Which of the following correctly matches these forms with a source of energy?

the covalent bonds of a sugar molecule: potential energy.

4

Bonds are a form of potential energy because the energy

arises from the relative positions of the atoms that form the bond.

5

Which of the following statements about the combustion of glucose with oxygen to form water and carbon dioxide (C6H12O6 + 6 O2 → 6 CO2 + 6 H2O) is correct?

The entropy of the products is greater than the entropy of the reactants.

A large molecule (glucose) has been converted into several smaller molecules (water and carbon dioxide); thus, the products have more disorder (greater entropy) than the reactants.

6

Which of the following statements about equilibrium of chemical reactions is correct?

A reactions that is at equilibrium is not capable of doing any work.

7

The ΔG for a reaction at equilibrium is zero, which means that

there is no free energy available to do any work.

8

Which of the following statements about ATP (adenosine triphosphate) is correct?

The cycling between ATP and ADP + Pi provides an energy coupling between catabolic and anabolic pathways.

9

Catabolic pathways provide the energy needed to make ATP from ADP and Pi. The hydrolysis of

ATP to ADP + Pi releases the same amount of energy.

10

Enzymes are described as catalysts, which means that they _____.

increase the rate of a reaction without being consumed by the reaction.

This permits enzyme molecules to be used repeatedly.

11

Which of the following would be unlikely to contribute to the substrate specificity of an enzyme?

The enzyme has an allosteric regulatory site.

The allosteric site is distinct from the active site, and does not affect the substrate specificity of the enzyme.

12

Which of the following would be likely to contribute to the substrate specificity of an enzyme?

-A hydrophobic group on the substrate interacts with several hydrophobic amino acids on the enzyme.
-A similar shape exists between a pocket on the surface of the enzyme and a functional group on the substrate.
-A positive charge on the substrate is attracted to a negative charge in the active site of the enzyme.
-The enzyme has the ability to change its configuration in response to the substrate binding.

13

Which of the following is NOT a way in which an enzyme can speed up the reaction that it catalyzes?

The active site can provide heat from the environment that raises the energy content of the substrate.

14

Which of the following are ways in which an enzyme can speed up the reaction that it catalyzes?

-The enzyme binds a cofactor that interacts with the substrate to facilitate the reaction.
-The binding of two substrates in the active site provides the correct orientation for them to react to form a product.
-The active site of the enzyme can provide a microenvironment with a different pH that facilitates the reaction.
-Binding of the substrate to the active site can stretch bonds in the substrate that need to be broken.

15

An enzyme cannot extract heat from the environment to speed a reaction. It can only

lower the activation energy barrier so that more substrates have the energy to react.

16

The binding of a compound to an enzyme is observed to slow down or stop the rate of the reaction catalyzed by the enzyme. Increasing the substrate concentration reduces the inhibitory effects of this compound. Which of the following could account for this observation?

The compound is a competitive inhibitor.

17

A competitive inhibitor slows down the enzyme by competing with the

substrate for binding at the active site. Increasing substrate concentrations will reduce the effectiveness of a competitive inhibitor.

18

Which of the following statements about feedback regulation of a metabolic pathway is correct?

The final product of a metabolic pathway is usually the compound that regulates the pathway.

It is quite common that the end product of the pathway controls the overall rate of the pathway.

19

Which of these is exhibiting kinetic energy?

a space station orbiting Earth.

20

Kinetic energy is

energy of motion.

21

"Conservation of energy" refers to the fact that _____.

energy cannot be created or destroyed but can be converted from one form to another

22

Chemical energy is a form of _____ energy.

potential

23

Chemical energy is a form of

stored energy.

24

In your body, what process converts the chemical energy found in glucose into the chemical energy found in ATP?

cellular respiration

25

Cellular respiration is the name given to the process by which the

body converts food energy to energy stored in ATP.

26

Which of these are by-products of cellular respiration?

heat, carbon dioxide, and water

27

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

exergonic.

Energy has been released.

28

A(n) _____ reaction occurs spontaneously.

exergonic

29

In exergonic reactions the products have

less potential energy than the reactants.

30

Which of these reactions requires a net input of energy from its surroundings?

endergonic

31

The products of endergonic reactions have

more potential energy than the reactants.

32

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

ATP

33

The hydrolysis of ATP provides

the energy needed for an endergonic reaction.

34

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

endergonic.

Energy has been acquired from the surroundings.

35

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

exergonic.

36

The energy released by an exergonic reaction can be used to

drive an endergonic reaction.

37

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.

By acquiring the phosphate group the reactant acquires energy.

38

What are the correct associations with each of these:
1. kinetic energy ...
2. enzyme ...
3. exergonic ...
4. potential energy ...

1. motion
2. protein
3. spontaneous
4. positional energy.

39

What is energy coupling?

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

40

What type of reaction breaks the bonds that join the phosphate groups in an ATP molecule?

hydrolysis

41

Hydrolysis involves

breaking bonds with the addition of water.

42

Adenosine triphosphate (ATP) is the high-energy form of adenosine because it contains the most phosphate groups (three). This molecule fuels many different endergonic (energy-requiring) enzymatic processes in biological organisms.

ATP molecules diffuse or are transported to the place where the energy is needed and deliver chemical energy from the breaking of their phosphate bonds.

43

Which part of the adenosine triphosphate molecule is released when it is hydrolyzed to provide energy for biological reactions?

- y(looks like a y) phosphate (the terminal phosphate)

The y (looks like a y kind of) -phosphate is the primary phosphate group on the ATP molecule that is hydrolyzed when energy is needed to drive anabolic reactions. Located the farthest from the ribose sugar, it has a higher energy than either the - or -phosphate.

44

In general, enzymes are what kinds of molecules?

proteins

45

Enzymes work by _____.

reducing the energy of activation (EA)

46

An enzyme

is an organic catalyst.

47

Enzymes are proteins that

behave as catalysts.

48

What name is given to the reactants in an enzymatically catalyzed reaction?

substrate

49

As a result of its involvement in a reaction, an enzyme _____.

is unchanged.

Enzymes are not changed as a result of their participation in a reaction.

50

The energy of activation must be overcome in order for

a reaction to proceed.

51

Consider a situation in which the enzyme is operating at optimum temperature and , and has been saturated with substrate. What is your best option for increasing the rate of the reaction?

increase the enzyme concentration.

If an enzyme is saturated with substrate, and it is operating at optimum and optimum temperature, there is very little that can be done except to increase the enzyme concentration. Some enzymes can be activated further by allosteric activators, in which case one might add some activator to the reaction. But otherwise, increasing the enzyme concentration is the only option.

52

A competitive inhibitor has a

structure that is so similar to the substrate that it can bond to the enzyme just like the substrate.

53

A noncompetitive inhibitor

binds to a site on the enzyme that is not the active site.

54

Usually, an irreversible inhibitor forms a

covalent bond with an amino acid side group within the active site, which prevents the substrate from entering the active site or prevents catalytic activity.

55

The competitive inhibitor competes with the

substrate for the active site on the enzyme.

56

When the noncompetitive inhibitor is bonded to the enzyme,

the shape of the enzyme is distorted.

57

Enzyme inhibitors disrupt normal interactions between an

enzyme and its substrate.

58

Competitive inhibitors compete physically and structurally with the substrate for an enzyme’s active site;

they can be outcompeted by adding extra substrate.

59

Noncompetitive inhibitors do not compete for the active site, but

inhibit the enzyme by binding elsewhere and changing the enzyme’s shape

60

Irreversible inhibitors bind directly to the active site by covalent bonds, which

change the structure of the enzyme and inactivate it permanently.

61

Most medications are

enzyme inhibitors of one kind or another.

62

You have added an irreversible inhibitor to a sample of enzyme and substrate. At this point, the reaction has stopped completely.
What can you do to regain the activity of the enzyme?

The enzyme is inactive at this point. New enzyme must be added to regain enzyme activity.

Because they bind directly to the active site by covalent bonds, irreversible inhibitors permanently render an enzyme inactive. Some drugs are irreversible inhibitors, including the antibiotic penicillin (which inhibits an enzyme involved in bacterial cell-wall synthesis) and aspirin (which inhibits cyclooxygenase-2, the enzyme involved in the inflammatory reaction).

63

You have an enzymatic reaction proceeding at the optimum pH and optimum temperature. You add a competitive inhibitor to the reaction and notice that the reaction slows down.
What can you do to speed the reaction up again?

Add more substrate; it will outcompete the inhibitor and increase the reaction rate.

Competitive inhibition can be overcome by adding more substrate to outcompete the inhibitor. Many drugs used to treat different medical conditions, including hypertension, are competitive inhibitors. It is fairly easy to make a molecule that is similar in structure to a particular substrate because the known enzyme’s shape can be used as a model of what the molecule needs to look like. It is more difficult to make a noncompetitive inhibitor because it is less obvious what the noncompetitive inhibitor’s shape and structure should be.

64

An enzyme is denatured when

it loses its native conformation and its biological activity.

65

An enzyme is considered a catalyst because

it speeds up chemical reactions without being used up.

66

An enzyme is considered specific because

of its ability to recognize the shape of a particular molecule.

67

A cofactor, such as a vitamin, binds to

an enzyme and plays a role in catalysis.

68

When properly aligned, the

enzyme and substrate form an enzyme-substrate (ES) complex.

69

A substrate binds to an enzyme at the

active site, where the reaction occurs.

70

In a catalyzed reaction a

reactant is often called a substrate.

71

A substrate binds at an enzyme’s active site;

the enzyme typically recognizes the specific shape of its substrate.

72

A cofactor, such as an inorganic ion or vitamin, may bind to the enzyme and assist in catalyzing the reaction.

The reaction environment must be appropriate for catalysis to proceed.

73

An enzyme will denature, or change its shape and lose its biological activity, at

too high a temperature or at a pH outside the enzyme’s optimal range.

74

Many enzymatic pathways are regulated by the feedback inhibition model described here.

In fact, it is so common that another name for it is end-product inhibition.

75

Which of the following best describes the main purpose of the combined processes of glycolysis and cellular respiration?

transforming the energy in glucose and related molecules in a chemical form that cells can use for work

76

The energy made available during cellular respiration is

coupled to a production of ATP, the basic energy currency that cells use for work.

77

In the combined processes of glycolysis and cellular respiration, what is consumed and what is produced?

Glucose is consumed, and carbon dioxide is produced.

78

The carbon in glucose is oxidized to

carbon dioxide during cellular respiration.

79

Which of the following describes the process of glycolysis?

It represents the first stage in the chemical oxidation of glucose by a cell.

80

Catabolism of glucose begins with

glycolysis.

81

A glucose molecule is completely broken down to carbon dioxide and water in glycolysis and the citric acid cycle, but together these two processes yield only a few molecules of ATP. What happened to most of the energy that the cell obtains from the oxidation of glucose?

It is stored in NADH and FADH2

82

The electrons obtained from the oxidation of glucose are temporarily stored in NADH and FADH2.

The energy derived from the oxidation of NADH and FADH2 is used to drive the electron transport chain and chemiosmotic synthesis of ATP.

83

Which statement about the citric acid cycle is correct?

The last reaction in the citric acid cycle produces a product that is a substrate for the first reaction of the citric acid cycle.

84

The electrons stripped from glucose in cellular respiration end up in which compound?

water.

85

At the end of the electron transport chain, the electrons and hydrogen atoms are added to

oxygen, forming water.

86

Which of the following statements about the chemiosmotic synthesis of ATP is correct?

The chemiosmotic synthesis of ATP requires that the electron transport in the inner mitochondrial membrane be coupled to proton transport across the same membrane.

87

Chemiosmosis uses the energy of a proton gradient to make ATP;

the proton gradient is formed by coupling the energy produced by electron transport with movement of protons across the membrane.

88

Which one of the following statements about the redox reactions of the electron transport chain is correct?

The redox reactions of the electron transport chain are directly coupled to the movement of protons across a membrane.

89

The reduction and oxidation of electron carriers in the electron transport chain provide the energy to

move protons across a membrane against the chemical gradient of protons.

90

In the absence of oxygen, what is the net gain of ATP for each glucose molecule that enters glycolysis?

two ATP.

Four ATP are made, but two ATP are consumed to start the process of glycolysis.

91

In most cells, not all of the carbon compounds that participate in glycolysis and the citric acid cycle are converted to carbon dioxide by cellular respiration. What happens to the carbon in these compounds that does not end up as CO2?

The carbon compounds are removed from these processes to serve as building blocks for other complex molecules.

92

Glycolysis and the citric acid cycle provide many compounds that are

the starting point for the synthesis of amino acids and lipids.

93

Chloroplasts are the sites of

photosynthesis.

94

Photosynthesis produces

glucose and releases oxygen into the atmosphere.

95

Mitochondria are the sites of

cellular respiration.

96

Carbon dioxide and water are the by-products of

cellular respiration.

97

Glycolysis occurs in the

cytosol.

98

The citric acid cycle transfers electrons to

NADH and FADH2.

99

Oxygen is the final electron acceptor of

cellular respiration.

100

Which term describes the degree to which an element attracts electrons?

electronegativity

101

Electronegativity is the tendency of an atom to

attract electrons toward itself.

102

Which terms describe two atoms when they form a bond in which electrons are completely transferred from one atom to the other?

Anion and Cation.

Each atom will carry a charge from the transfer of electrons.

103

Which of the following statements is not true of most cellular redox reactions?

A hydrogen atom is transferred to the atom that loses an electron.

104

Which of the following statements are true of most cellular redox reactions?

-Changes in potential energy can be released as heat.
-The reactant that is oxidized loses electrons.
-The electron acceptor is reduced.
-A hydrogen atom (proton, or H+) is often transferred to the atom that gains an electron

105

How many NADH are produced by glycolysis?

2.

106

Two NADH molecules are produced by

glycolysis.

107

In glycolysis, ATP molecules are produced by _____.

substrate-level phosphorylation.

A phosphate group is transferred from glyceraldehyde phosphate to ADP.

108

Which of these is NOT a product of glycolysis?

FADH2.

109

FADH2 is a product of the

citric acid cycle.

110

Which of these are products of glycolysis?

pyruvate
NADH
ATP

111

In glycolysis, what starts the process of glucose oxidation?

ATP.

Some ATP energy is used to start the process of glucose oxidation.

112

In glycolysis there is a net gain of _____ ATP.

2.


It takes 2 ATP to produce 4 ATP.

113

In glycolysis, as in all the stages of cellular respiration, the transfer of electrons from electron donors to electron acceptors plays a critical role in the overall conversion of the energy in foods to energy in ATP.

These reactions involving electron transfers are known as oxidation-reduction, or redox, reactions.

114

When a compound donates (loses) electrons, that compound becomes

oxidized. Such a compound is often referred to as an electron donor.

115

When a compound accepts (gains) electrons, that compound becomes

reduced. Such a compound is often referred to as an electron acceptor.

116

In glycolysis, the carbon-containing compound that functions as the electron donor is

glucose.

117

Once the electron donor in glycolysis gives up its electrons,

it is oxidized to a compound called pyruvate.

118

NAD+ is the compound that functions as the

electron acceptor in glycolysis.

119

The reduced form of the electron acceptor in glycolysis is

NADH.

120

In the net reaction for glycolysis, glucose (the electron donor) is oxidized to

pyruvate. The electrons removed from glucose are transferred to the electron acceptor, NAD+, creating NADH.

121

Which of these enters the citric acid cycle?

acetyl CoA.

Acetyl CoA is a reactant in the citric acid cycle

122

In the citric acid cycle, ATP molecules are produced by _____.

substrate-level phosphorylation.

A phosphate group is transferred from GTP to ADP.

123

Which of these is NOT a product of the citric acid cycle?

acetyl CoA.

124

Acetyl CoA enters the

citric acid cycle.

125

Which of these are products of the citric acid cycle?

ATP
NADH + H^+
FADH2
CO2

126

During acetyl CoA formation and the citric acid cycle,

all of the carbon atoms that enter cellular respiration in the glucose molecule are released in the form of CO2.

127

The net result of this complex series of reactions in the citric acid cycle is the

complete oxidation of the two carbon atoms in the acetyl group of acetyl CoA to two molecules of CO2.

128

In the sequential reactions of acetyl CoA formation and the citric acid cycle, pyruvate (the output from glycolysis) is completely oxidized, and the

electrons produced from this oxidation are passed on to two types of electron acceptors.

129

Pyruvate is oxidized to

CO2

130

NAD+ is reduced to

NADH

131

FAD is reduced to

FADH2

132

As in glycolysis, the electrons removed from carbon-containing intermediates during acetyl CoA formation and the citric acid cycle are passed to the electron carrier NAD+, reducing it to NADH.

The citric acid cycle also uses a second electron carrier, FAD (flavin adenine dinucleotide), the oxidized form, and FADH2, the reduced form.

133

Why is the citric acid cycle a cyclic pathway rather than a linear pathway?
In the oxidation of pyruvate to acetyl CoA, one carbon atom is released as CO2. However, the oxidation of the remaining two carbon atoms—in acetate—to CO2 requires a complex, eight-step pathway—the citric acid cycle. Consider four possible explanations for why the last two carbons in acetate are converted to CO2 in a complex cyclic pathway rather than through a simple, linear reaction.
Use your knowledge of the first three stages of cellular respiration to determine which explanation is correct.

It is easier to remove electrons and produce CO2 from compounds with three or more carbon atoms than from a two-carbon compound such as acetyl CoA.

Although it is possible to oxidize the two-carbon acetyl group of acetyl CoA to two molecules of CO2, it is much more difficult than adding the acetyl group to a four-carbon acid to form a six-carbon acid (citrate). Citrate can then be oxidized sequentially to release two molecules of CO2.

134

For each glucose that enters glycolysis, _____ acetyl CoA enter the citric acid cycle.

2

135

Each glucose produces two pyruvates,

each of which is converted into acetyl CoA.

136

For each glucose that enters glycolysis, _____ NADH + H+ are produced by the citric acid cycle.

6

137

3 NADH + H+ are produced per

each acetyl CoA that enters the citric acid cycle.

138

In cellular respiration, most ATP molecules are produced by _____.

oxidative phosphorylation.

This process utilizes energy released by electron transport.

139

The final electron acceptor of cellular respiration is _____.

oxygen.

Oxygen is combined with electrons and hydrogen to form water.

140

During electron transport, energy from _____ is used to pump hydrogen ions into the _____.

NADH and FADH2 ... intermembrane space

141

The energy released as electrons, which have been donated by NADH and FADH2, is passed along the electron transport chain and

used to pump hydrogen ions into the intermembrane space.

142

ATP synthase phosphorylates

ADP.

143

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

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

144

Concentration gradients are a form of

potential energy.

145

The reactions of cellular respiration can be broken down into four stages:

1. glycolysis
2. acetyl coenzyme A (acetyl CoA) formation
3. citric acid cycle (also known as the Krebs cycle)
4. oxidative phosphorylation (electron transport and chemiosmotic ATP synthesis)

146

Glycolysis occurs in the

cytosol
(cytoplasm)

147

acetyl CoA formation occurs in the

mitochondrial matrix

148

the citric acid cycle occurs in the

mitochondrial matrix

149

oxidative phosphorylation occurs in the

inner mitochondrial membrane

150

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.

151

Oxidative phosphorylation consists of two tightly linked processes - electron transport and ATP synthesis. In electron transport, the NADH and FADH2 produced in the first three stages of cellular respiration are oxidized by O2 (the oxidative part of this stage).

These redox reactions also drive the pumping of protons across the inner mitochondrial membrane, creating a proton ( H+) gradient. This H+ gradient is used to power the chemiosmotic synthesis of ATP from ADP and Pi (the phosphorylation part of this stage).

152

In mitochondrial electron transport, what is the direct role of O2?

to function as the final electron acceptor in the electron transport chain

153

The only place that O2 participates in cellular respiration is at the end of the electron transport chain, as the final electron acceptor.

Oxygen's high affinity for electrons ensures its success in this role. Its contributions to driving electron transport, forming a proton gradient, and synthesizing ATP are all indirect effects of its role as the terminal electron acceptor.

154

How would anaerobic conditions (when no O2 is present) affect the rate of electron transport and ATP production during oxidative phosphorylation? (Note that you should not consider the effect on ATP synthesis in glycolysis or the citric acid cycle.)

Both electron transport and ATP synthesis would stop.

155

Oxygen plays an essential role in cellular respiration because it is the final electron acceptor for the entire process. Without O2, mitochondria are unable to oxidize the NADH and FADH2 produced in the first three steps of cellular respiration, and thus cannot make any ATP via oxidative phosphorylation.

In addition, without O2 the mitochondria cannot oxidize the NADH and FADH2 back to NAD+ and FAD, which are needed as inputs to the first three stages of cellular respiration.

156

he rate of cellular respiration is regulated by its

major product, ATP, via feedback inhibition

157

high levels of ATP inhibit phosphofructokinase (PFK), an early enzyme in glycolysis. As a result,

the rate of cellular respiration, and thus ATP production, decreases. Feedback inhibition enables cells to adjust their rate of cellular respiration to match their demand for ATP.

158

Suppose that a cell’s demand for ATP suddenly exceeds its supply of ATP from cellular respiration.
Which statement correctly describes how this increased demand would lead to an increased rate of ATP production?

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

159

An increased demand for ATP by a cell will cause an initial decrease in the level of cellular ATP.

Lower ATP decreases the inhibition of the PFK enzyme, thus increasing the rate of glycolysis, cellular respiration, and ATP production. It is the initial decrease in ATP levels that leads to an increase in ATP production.

160

In muscle cells, fermentation produces _____.

lactate and NAD^+.

161

In fermentation _____ is reduced and _____ is oxidized.

pyruvate ... NADH

The pyruvate from glycolysis is reduced to either lactate or ethanol, and NADH is oxidized to NAD+.

162

Which molecule is metabolized in a cell to produce energy for performing work?

glucose.

163

Glucose is used to produce

high-energy ATP in a cell.

164

The potential energy in an ATP molecule is derived mainly from

its three phosphate groups.

165

The three phosphate groups in an ATP molecule carry negative charges that

strongly repel each other and give ATP a large amount of potential energy.

166

Which process is not part of the cellular respiration pathway that produces large amounts of ATP in a cell?

fermentation.

167

Fermentation is an alternate pathway used when

oxygen levels are low.

168

Which processes are part of the cellular respiration pathway that produces large amounts of ATP in a cell?

Electron transport chain
Krebs cycle
Glycolysis

169

Which step of the cellular respiration pathway can take place in the absence of oxygen?

Glycolysis

170

Glycolysis can take place in the absence of oxygen; its product, pyruvate, enters the

cellular respiration pathway or undergoes fermentation depending on the availability of oxygen.

171

Into which molecule are all the carbon atoms in glucose ultimately incorporated during cellular respiration?

Carbon dioxide.

All of the carbon atoms in glucose are incorporated into carbon dioxide: Two molecules are formed as pyruvate is converted to acetyl CoA, and four molecules are formed during the Krebs cycle.

172

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

NADH and FADH2 donate their electrons to the chain.

The electrons lose energy as they move down the chain, and this energy is used to create a proton gradient that drives the synthesis of ATP.

173

Which stage of glucose metabolism produces the most ATP?

Electron transport and chemiosmosis

174

Electron transport and chemiosmosis (oxidative phosphorylation) can yield around

26 molecules of ATP.

175

The reactions that generate the largest amounts of ATP during cellular respiration take place in

the mitochondria.

176

Glycolysis takes place in the cytoplasm, whereas the Krebs cycle and the electron transport chain, which generate the largest amounts of ATP during cellular respiration, take place in

the mitochondria.

177

fermentation in human muscle produces

lactate

178

fermentation in yeast and bacteria produces

ethanol

179

aerobic oxidation produces

acetyl CoA

180

In the presence of oxygen, human cells carry out aerobic respiration, which yields

acetyl CoA.

181

In the absence of oxygen, human cells can carry out lactic acid fermentation, which yields

lactate.

182

Yeasts and many bacteria carry out alcohol fermentation, which takes place under anaerobic conditions, and produces

ethanol.

183

Reactants in the anaerobic reduction of pyruvate during lactic acid fermentation

pyruvate
NADH

184

Products in the anaerobic reduction of pyruvate during lactic acid fermentation

lactate
NAD^+

185

When an animal engages in strenuous usage of its muscles, anaerobic conditions ensue, and pyruvate is reduced to lactate.

In the process, NADH is oxidized to NAD+. This NAD+ can further oxidize glyceraldehyde-3-phosphate to produce more ATP.

186

Chloroplasts are the sites of

photosynthesis.

187

Photosynthesis produces

glucose and releases oxygen into the atmosphere.

188

Mitochondria are the sites of

cellular respiration.

189

Carbon dioxide and water are the by-products of

cellular respiration.

190

Glycolysis occurs in the

cytosol.

191

The citric acid cycle transfers electrons to

NADH and FADH2.

192

Oxygen is the final electron acceptor of

cellular respiration.

193

Which term describes the degree to which an element attracts electrons?

electronegativity

194

Electronegativity is the tendency of an atom to

attract electrons toward itself.

195

Which terms describe two atoms when they form a bond in which electrons are completely transferred from one atom to the other?

Anion and Cation.

Each atom will carry a charge from the transfer of electrons.

196

Which of the following statements is not true of most cellular redox reactions?

A hydrogen atom is transferred to the atom that loses an electron.

197

Which of the following statements are true of most cellular redox reactions?

-Changes in potential energy can be released as heat.
-The reactant that is oxidized loses electrons.
-The electron acceptor is reduced.
-A hydrogen atom (proton, or H+) is often transferred to the atom that gains an electron

198

How many NADH are produced by glycolysis?

2.

199

Two NADH molecules are produced by

glycolysis.

200

In glycolysis, ATP molecules are produced by _____.

substrate-level phosphorylation.

A phosphate group is transferred from glyceraldehyde phosphate to ADP.

201

Which of these is NOT a product of glycolysis?

FADH2.

202

FADH2 is a product of the

citric acid cycle.

203

Which of these are products of glycolysis?

pyruvate
NADH
ATP

204

In glycolysis, what starts the process of glucose oxidation?

ATP.

Some ATP energy is used to start the process of glucose oxidation.

205

In glycolysis there is a net gain of _____ ATP.

2.


It takes 2 ATP to produce 4 ATP.

206

In glycolysis, as in all the stages of cellular respiration, the transfer of electrons from electron donors to electron acceptors plays a critical role in the overall conversion of the energy in foods to energy in ATP.

These reactions involving electron transfers are known as oxidation-reduction, or redox, reactions.

207

When a compound donates (loses) electrons, that compound becomes

oxidized. Such a compound is often referred to as an electron donor.

208

When a compound accepts (gains) electrons, that compound becomes

reduced. Such a compound is often referred to as an electron acceptor.

209

In glycolysis, the carbon-containing compound that functions as the electron donor is

glucose.

210

Once the electron donor in glycolysis gives up its electrons,

it is oxidized to a compound called pyruvate.

211

NAD+ is the compound that functions as the

electron acceptor in glycolysis.

212

The reduced form of the electron acceptor in glycolysis is

NADH.

213

In the net reaction for glycolysis, glucose (the electron donor) is oxidized to

pyruvate. The electrons removed from glucose are transferred to the electron acceptor, NAD+, creating NADH.

214

Which of these enters the citric acid cycle?

acetyl CoA.

Acetyl CoA is a reactant in the citric acid cycle

215

In the citric acid cycle, ATP molecules are produced by _____.

substrate-level phosphorylation.

A phosphate group is transferred from GTP to ADP.

216

Which of these is NOT a product of the citric acid cycle?

acetyl CoA.

217

Acetyl CoA enters the

citric acid cycle.

218

Which of these are products of the citric acid cycle?

ATP
NADH + H^+
FADH2
CO2

219

During acetyl CoA formation and the citric acid cycle,

all of the carbon atoms that enter cellular respiration in the glucose molecule are released in the form of CO2.

220

The net result of this complex series of reactions in the citric acid cycle is the

complete oxidation of the two carbon atoms in the acetyl group of acetyl CoA to two molecules of CO2.

221

In the sequential reactions of acetyl CoA formation and the citric acid cycle, pyruvate (the output from glycolysis) is completely oxidized, and the

electrons produced from this oxidation are passed on to two types of electron acceptors.

222

Pyruvate is oxidized to

CO2

223

NAD+ is reduced to

NADH

224

FAD is reduced to

FADH2

225

As in glycolysis, the electrons removed from carbon-containing intermediates during acetyl CoA formation and the citric acid cycle are passed to the electron carrier NAD+, reducing it to NADH.

The citric acid cycle also uses a second electron carrier, FAD (flavin adenine dinucleotide), the oxidized form, and FADH2, the reduced form.

226

Why is the citric acid cycle a cyclic pathway rather than a linear pathway?
In the oxidation of pyruvate to acetyl CoA, one carbon atom is released as CO2. However, the oxidation of the remaining two carbon atoms—in acetate—to CO2 requires a complex, eight-step pathway—the citric acid cycle. Consider four possible explanations for why the last two carbons in acetate are converted to CO2 in a complex cyclic pathway rather than through a simple, linear reaction.
Use your knowledge of the first three stages of cellular respiration to determine which explanation is correct.

It is easier to remove electrons and produce CO2 from compounds with three or more carbon atoms than from a two-carbon compound such as acetyl CoA.

Although it is possible to oxidize the two-carbon acetyl group of acetyl CoA to two molecules of CO2, it is much more difficult than adding the acetyl group to a four-carbon acid to form a six-carbon acid (citrate). Citrate can then be oxidized sequentially to release two molecules of CO2.

227

For each glucose that enters glycolysis, _____ acetyl CoA enter the citric acid cycle.

2

228

Each glucose produces two pyruvates,

each of which is converted into acetyl CoA.

229

For each glucose that enters glycolysis, _____ NADH + H+ are produced by the citric acid cycle.

6

230

3 NADH + H+ are produced per

each acetyl CoA that enters the citric acid cycle.

231

In cellular respiration, most ATP molecules are produced by _____.

oxidative phosphorylation.

This process utilizes energy released by electron transport.

232

The final electron acceptor of cellular respiration is _____.

oxygen.

Oxygen is combined with electrons and hydrogen to form water.

233

During electron transport, energy from _____ is used to pump hydrogen ions into the _____.

NADH and FADH2 ... intermembrane space

234

The energy released as electrons, which have been donated by NADH and FADH2, is passed along the electron transport chain and

used to pump hydrogen ions into the intermembrane space.

235

ATP synthase phosphorylates

ADP.

236

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

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

237

Concentration gradients are a form of

potential energy.

238

The reactions of cellular respiration can be broken down into four stages:

1. glycolysis
2. acetyl coenzyme A (acetyl CoA) formation
3. citric acid cycle (also known as the Krebs cycle)
4. oxidative phosphorylation (electron transport and chemiosmotic ATP synthesis)

239

Glycolysis occurs in the

cytosol
(cytoplasm)

240

acetyl CoA formation occurs in the

mitochondrial matrix

241

the citric acid cycle occurs in the

mitochondrial matrix

242

oxidative phosphorylation occurs in the

inner mitochondrial membrane

243

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.

244

Oxidative phosphorylation consists of two tightly linked processes - electron transport and ATP synthesis. In electron transport, the NADH and FADH2 produced in the first three stages of cellular respiration are oxidized by O2 (the oxidative part of this stage).

These redox reactions also drive the pumping of protons across the inner mitochondrial membrane, creating a proton ( H+) gradient. This H+ gradient is used to power the chemiosmotic synthesis of ATP from ADP and Pi (the phosphorylation part of this stage).

245

In mitochondrial electron transport, what is the direct role of O2?

to function as the final electron acceptor in the electron transport chain

246

The only place that O2 participates in cellular respiration is at the end of the electron transport chain, as the final electron acceptor.

Oxygen's high affinity for electrons ensures its success in this role. Its contributions to driving electron transport, forming a proton gradient, and synthesizing ATP are all indirect effects of its role as the terminal electron acceptor.

247

How would anaerobic conditions (when no O2 is present) affect the rate of electron transport and ATP production during oxidative phosphorylation? (Note that you should not consider the effect on ATP synthesis in glycolysis or the citric acid cycle.)

Both electron transport and ATP synthesis would stop.

248

Oxygen plays an essential role in cellular respiration because it is the final electron acceptor for the entire process. Without O2, mitochondria are unable to oxidize the NADH and FADH2 produced in the first three steps of cellular respiration, and thus cannot make any ATP via oxidative phosphorylation.

In addition, without O2 the mitochondria cannot oxidize the NADH and FADH2 back to NAD+ and FAD, which are needed as inputs to the first three stages of cellular respiration.

249

he rate of cellular respiration is regulated by its

major product, ATP, via feedback inhibition

250

high levels of ATP inhibit phosphofructokinase (PFK), an early enzyme in glycolysis. As a result,

the rate of cellular respiration, and thus ATP production, decreases. Feedback inhibition enables cells to adjust their rate of cellular respiration to match their demand for ATP.

251

Suppose that a cell’s demand for ATP suddenly exceeds its supply of ATP from cellular respiration.
Which statement correctly describes how this increased demand would lead to an increased rate of ATP production?

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

252

An increased demand for ATP by a cell will cause an initial decrease in the level of cellular ATP.

Lower ATP decreases the inhibition of the PFK enzyme, thus increasing the rate of glycolysis, cellular respiration, and ATP production. It is the initial decrease in ATP levels that leads to an increase in ATP production.

253

In muscle cells, fermentation produces _____.

lactate and NAD^+.

254

In fermentation _____ is reduced and _____ is oxidized.

pyruvate ... NADH

The pyruvate from glycolysis is reduced to either lactate or ethanol, and NADH is oxidized to NAD+.

255

Which molecule is metabolized in a cell to produce energy for performing work?

glucose.

256

Glucose is used to produce

high-energy ATP in a cell.

257

The potential energy in an ATP molecule is derived mainly from

its three phosphate groups.

258

The three phosphate groups in an ATP molecule carry negative charges that

strongly repel each other and give ATP a large amount of potential energy.

259

Which process is not part of the cellular respiration pathway that produces large amounts of ATP in a cell?

fermentation.

260

Fermentation is an alternate pathway used when

oxygen levels are low.

261

Which processes are part of the cellular respiration pathway that produces large amounts of ATP in a cell?

Electron transport chain
Krebs cycle
Glycolysis

262

Which step of the cellular respiration pathway can take place in the absence of oxygen?

Glycolysis

263

Glycolysis can take place in the absence of oxygen; its product, pyruvate, enters the

cellular respiration pathway or undergoes fermentation depending on the availability of oxygen.

264

Into which molecule are all the carbon atoms in glucose ultimately incorporated during cellular respiration?

Carbon dioxide.

All of the carbon atoms in glucose are incorporated into carbon dioxide: Two molecules are formed as pyruvate is converted to acetyl CoA, and four molecules are formed during the Krebs cycle.

265

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

NADH and FADH2 donate their electrons to the chain.

The electrons lose energy as they move down the chain, and this energy is used to create a proton gradient that drives the synthesis of ATP.

266

Which stage of glucose metabolism produces the most ATP?

Electron transport and chemiosmosis

267

Electron transport and chemiosmosis (oxidative phosphorylation) can yield around

26 molecules of ATP.

268

The reactions that generate the largest amounts of ATP during cellular respiration take place in

the mitochondria.

269

Glycolysis takes place in the cytoplasm, whereas the Krebs cycle and the electron transport chain, which generate the largest amounts of ATP during cellular respiration, take place in

the mitochondria.

270

fermentation in human muscle produces

lactate

271

fermentation in yeast and bacteria produces

ethanol

272

aerobic oxidation produces

acetyl CoA

273

In the presence of oxygen, human cells carry out aerobic respiration, which yields

acetyl CoA.

274

In the absence of oxygen, human cells can carry out lactic acid fermentation, which yields

lactate.

275

Yeasts and many bacteria carry out alcohol fermentation, which takes place under anaerobic conditions, and produces

ethanol.

276

Reactants in the anaerobic reduction of pyruvate during lactic acid fermentation

pyruvate
NADH

277

Products in the anaerobic reduction of pyruvate during lactic acid fermentation

lactate
NAD^+

278

When an animal engages in strenuous usage of its muscles, anaerobic conditions ensue, and pyruvate is reduced to lactate.

In the process, NADH is oxidized to NAD+. This NAD+ can further oxidize glyceraldehyde-3-phosphate to produce more ATP.

279

Which of the following correctly states the relationship between anabolic and catabolic pathways?

Anabolic pathways synthesize more complex organic molecules using the energy derived from catabolic pathways.

280

Which of the following situations does NOT represent an energy transformation?

the coupling of ATP hydrolysis to the production of a proton gradient across a membrane by a proton pump

281

Organisms are described as thermodynamically open systems. Which of the following statements is consistent with this description?

Organisms acquire energy from, and lose energy to, their surroundings.

282

Consider the growth of a farmer's crop over a season. Which of the following correctly states a limitation imposed by the first or second law of thermodynamics?

To obey the first law, the crops must represent an open system.

283

Which of the following states the relevance of the first law of thermodynamics to biology?

Energy can be freely transformed among different forms as long as the total energy is conserved.

284

Which is the most abundant form of energy in a cell?

Chemical energy

285

Which of the following is an example of the second law of thermodynamics as it applies to biological reactions?

The aerobic respiration of one molecule of glucose produces six molecules each of carbon dioxide and water.

The second law of thermodynamics states that every energy transformation makes the universe more disordered—carbon dioxide and water are more disordered than glucose.

286

According to the second law of thermodynamics, which of the following is true?

The decrease in entropy associated with life must be compensated for by increased entropy in the environment in which life exists.

287

If the entropy of a living organism is decreasing, which of the following is most likely to be occurring simultaneously?

Energy input into the organism must be occurring to drive the decrease in entropy.

288

Which of the following has the most free energy per molecule?

a starch molecule

289

The electronic arrangement in which of the following molecules means that this (these) molecule(s) has/have greater free energy than the others?

methane

290

Which part of the equation ΔG = ΔH - TΔS tells you if a process is spontaneous?

ΔG

291

If, during a process, the system becomes more ordered, then _____.

ΔS is negative

292

When one molecule is broken down into six component molecules, which of the following will always be true?

ΔS is positive.

293

From the equation ΔG = ΔH - TΔS it is clear that _____.

-a decrease in the system's total energy will increase the probability of spontaneous change
-increasing the entropy of a system will increase the probability of spontaneous change
-increasing the temperature of a system will increase the probability of spontaneous change

294

An exergonic (spontaneous) reaction is a chemical reaction that _____.

releases energy when proceeding in the forward direction

295

Which of the following reactions would be endergonic?

glucose + fructose → sucrose

296

Molecules A and B contain 110 kcal/mol of free energy and molecules B and C contain 150 kcal/mol of energy. A and B are converted to C and D. What can be concluded?

The reaction that proceeds to convert A and B to C and D is endergonic; the products are more organized than the reactants.

C and D contain more energy than do A and B; therefore they are more organized and their construction required an input of energy.

297

Which of the following determines the sign of ΔG for a reaction?

the free energy of the reactants and the free energy of the products

298

Metabolic pathways in cells are typically far from equilibrium. Which of the following processes tend(s) to keep these pathways away from equilibrium?

-the continuous removal of the products of a pathway to be used in other reactions
-an input of free energy from outside the pathway

299

Which of the following is an example of the cellular work accomplished with the free energy derived from the hydrolysis of ATP, involved in the production of electrochemical gradients?

proton movement against a gradient of protons

300

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

releasing free energy that can be coupled to other reactions

301

Which of the following statements correctly describes some aspect of ATP hydrolysis being used to drive the active transport of an ion into the cell against the ion's concentration gradient?

This is an example of energy coupling.

302

Much of the suitability of ATP as an energy intermediary is related to the instability of the bonds between the phosphate groups. These bonds are unstable because _____.

the negatively charged phosphate groups vigorously repel one another and the terminal phosphate group is more stable in water than it is in ATP

303

When 1 mole of ATP is hydrolyzed in a test tube without an enzyme, about twice as much heat is given off as when 1 mole of ATP is hydrolyzed in a cell. Which of the following best explains these observations?

In the cell, the hydrolysis of ATP is coupled to other endergonic reactions.

304

What best characterizes the role of ATP in cellular metabolism?

The free energy released by ATP hydrolysis may be coupled to an endergonic process via the formation of a phosphorylated intermediate.

305

The formation of glucose-6-phosphate from glucose is an endergonic reaction and is coupled to which of the following reactions or pathways?

the hydrolysis of ATP

306

A chemical reaction is designated as exergonic rather than endergonic when _____.

the potential energy of the products is less than the potential energy of the reactants

307

Which of the following is changed by the presence of an enzyme in a reaction?

the activation energy

308

What do the sign and magnitude of the ΔG of a reaction tell us about the speed of the reaction?

Neither the sign nor the magnitude of ΔG have anything to do with the speed of a reaction.

309

How do enzymes lower activation energy?

by locally concentrating the reactants

310

Which of the following statements about enzymes is true?

Enzymes speed up the rate of the reaction without changing the DG for the reaction.

311

Which of the following statements about enzyme function is correct?

Enzymes can lower the activation energy of reactions, but they cannot change the equilibrium point because they cannot change the net energy output.

312

A plot of reaction rate (velocity) against temperature for an enzyme indicates little activity at 10°C and 45°C, with peak activity at 35°C. The most reasonable explanation for the low velocity at 10°C is that _____.

there is too little activation energy available

313

Which of the following statements about enzymes is incorrect?

An enzyme is consumed during the reaction it catalyzes.

314

Which of the following statements about enzymes is correct?

-An enzyme lowers the activation energy of a chemical reaction.
-Enzymes can be used to accelerate both anabolic and catabolic reactions.
-An enzyme is very specific in terms of which substrate it binds to.
-Most enzymes are proteins.

315

Which of the following statements about the active site of an enzyme is correct?

The active site may resemble a groove or pocket in the surface of a protein into which the substrate fits.

316

What is meant by the "induced fit" of an enzyme?

The enzyme changes its shape slightly as the substrate binds to it

317

Which of the following statements correctly describe(s) the role(s) of heat in biological reactions?

-Heat from the environment is necessary for substrates to get over the activation energy barrier.
-The kinetic energy of the substrates is increased as the amount of heat in the system is increased.

318

Above a certain substrate concentration, the rate of an enzyme-catalyzed reaction drops as the enzymes become saturated. Which of the following would lead to a faster conversion of substrate into product under these saturated conditions?

-an increase in concentration of enzyme
-increasing the temperature by a few degrees

319

Enzyme activity is affected by pH because _____.

high or low pH may disrupt hydrogen bonding or ionic interactions and thus change the shape of the active site

320

Which of these statements about enzyme inhibitors is true?

The action of competitive inhibitors may be reversible or irreversible.

321

Succinylcholine is structurally almost identical to acetylcholine. If succinylcholine is added to a mixture that contains acetylcholine and the enzyme that hydrolyzes acetylcholine (but not succinylcholine), the rate of acetylcholine hydrolysis is decreased. Subsequent addition of more acetylcholine restores the original rate of acetylcholine hydrolysis. Which of the following correctly explains this observation?

Succinylcholine must be a competitive inhibitor with acetylcholine.

322

The process of stabilizing the structure of an enzyme in its active form by the binding of a molecule is an example of _____.

allosteric regulation

323

Which of the following statements about allosteric proteins is/are true?

-They exist in active and inactive conformations.
-They are acted on by inhibitors.
-They are sensitive to environmental conditions.

324

The binding of an allosteric inhibitor to an enzyme causes the rate of product formation by the enzyme to decrease. Which of the following best explains why this decrease occurs?

The allosteric inhibitor causes a structural change in the enzyme that prevents the substrate from binding at the active site.

325

Under most conditions, the supply of energy by catabolic pathways is regulated by the demand for energy by anabolic pathways. Considering the role of ATP formation and hydrolysis in energy coupling of anabolic and catabolic pathways, which of the following statements is most likely to be true?

High levels of ADP act as an allosteric activator of catabolic pathways

326

A molecule becomes more oxidized when it _____.

loses an electron

327

In the overall process of glycolysis and cellular respiration, _____ is oxidized and _____ is reduced.

glucose ... oxygen

328

Most of the ATP produced in cellular respiration comes from which of the following processes?

oxidative phosphorylation

329

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

oxidation of glucose to pyruvate; oxidation of pyruvate; oxidation of acetyl-coA; oxidative phosphorylation

330

Oxygen gas (O2) is one of the strongest oxidizing agents known. The explanation for this is that _____.

the oxygen atom is very electronegative

331

The function of cellular respiration is to _____.

extract usable energy from glucose.

The most prevalent and efficient catabolic pathway is cellular respiration, in which oxygen is consumed as a reactant, along with the organic fuel (frequently glucose).

332

During the reaction C6H12O6 + 6 O2 → 6 CO2 + 6 H2O, which compound is reduced as a result of the reaction?

oxygen

333

Each ATP molecule contains about 1% of the amount of chemical energy available from the complete oxidation of a single glucose molecule. Cellular respiration produces about 32 ATP from one glucose molecule. What happens to the rest of the energy in glucose?

It is converted to heat.

The process is only about 38% efficient, with the rest of the energy lost as heat.

334

Which of the following statements is the best explanation of what happens to the temperature and carbon dioxide concentration during a one-hour class period in a classroom of 300 students if the heating and air conditioning is turned off and all doors are kept closed?

Temperature and the level of carbon dioxide rise as heat and carbon dioxide are by-products of cellular respiration.

The oxidation of organic molecules produces carbon dioxide, and as the exergonic process of cellular respiration is not 100% efficient, some energy is lost to the environment as heat.

335

A small amount of ATP is made in glycolysis by which of the following processes?

transfer of a phosphate group from a fragment of glucose to ADP by substrate-level phosphorylation

336

Where do the reactions of glycolysis occur in a eukaryotic cell?

the cytosol

337

A chemist has discovered a drug that blocks phosphoglucoisomerase, an enzyme that catalyzes the second reaction in glycolysis. He wants to use the drug to kill bacteria in people with infections. However, he cannot do this because _____.

human cells must also perform glycolysis; the drug might also poison them

338

In glycolysis, there is no production of carbon dioxide as a product of the pathway. Which of the following is the best explanation for this?

The products of glycolysis contain the same total number of carbon atoms as in the starting material.

339

Of the following molecules in the glycolytic pathway (the process of glycolysis), the one with the most chemical energy is _____.

fructose-1,6-bisphosphate

340

Most of the NADH that delivers electrons to the electron transport chain comes from which of the following processes?

the citric acid cycle

341

In an experiment, mice were fed glucose (C6H12O6) containing a small amount of radioactive oxygen. The mice were closely monitored, and after a few minutes radioactive oxygen atoms showed up in _____.

carbon dioxide.

One molecule of CO2 is formed when pyruvate is converted to acetyl CoA, and two molecules of CO2 are produced in the citric acid cycle.

342

In preparing pyruvate to enter the citric acid cycle, which of the following steps occurs?

Pyruvate is oxidized and decarboxylated, and the removed electrons are used to reduce an NAD+ to an NADH.

In addition to these events, a molecule of coenzyme A is attached to the resulting acetyl group.

343

Why is the citric acid cycle called a cycle?

The four-carbon acid that accepts the acetyl CoA in the first step of the cycle is regenerated by the last step of the cycle.

344

In the citric acid cycle, for each pyruvate that enters the cycle, one ATP, three NADH, and one FADH2 are produced. For each glucose molecule that enters glycolysis, how many ATP, NADH, and FADH2 are produced in the citric acid cycle?

two ATP, six NADH, two FADH2

345

Where do the reactions of the citric acid cycle occur in eukaryotic cells?

the matrix of the mitochondrion

346

How many molecules of ATP are gained by substrate-level phosphorylation from the complete breakdown of a single molecule of glucose in the presence of oxygen?

four

347

Which of the following represents the major (but not the only) energy accomplishment of the citric acid cycle?

formation of NADH and FADH2

348

After completion of the citric acid cycle, most of the usable energy from the original glucose molecule is in the form of _____.

NADH

349

Which of the following accompanies the conversion of pyruvate to acetyl CoA before the citric acid cycle?

release of CO2 and synthesis of NADH

350

The energy given up by electrons as they move through the electron transport chain is used in which of the following processes?

pumping H+ across a membrane

351

The ATP synthase in a human cell obtains energy for synthesizing ATP directly from which of the following processes?

the flow of H+ across the inner mitochondrial membrane through the ATP synthase enzyme

352

When a poison such as cyanide blocks the electron transport chain, glycolysis and the citric acid cycle also eventually stop working. Which of the following is the best explanation for this?

NAD+ and FAD are not available for glycolysis and the citric acid cycle to continue.

353

Most of the electrons removed from glucose by cellular respiration are used for which of the following processes?

-reducing NAD+ to NADH in glycolysis and the citric acid cycle
-producing a proton gradient for ATP synthesis in the mitochondria

354

Which part of the catabolism of glucose by cellular respiration requires molecular oxygen (O2) and produces CO2?

the combination of the citric acid cycle and electron transport

355

During aerobic respiration, molecular oxygen (O2) is used for which of the following purposes?

at the end of the electron transport chain to accept electrons and form H2O

O2 is the final electron acceptor.

356

Which of the following substances is/are involved in oxidative phosphorylation?

ADP
Oxygen
ATP

357

Which of the following best describes the electron transport chain?

Electrons are passed from one carrier to another, releasing a little energy at each step.

358

Which of the following is the source of the energy that produces the chemiosmotic gradient in mitochondria?

electrons moving down the electron transport chain

359

During respiration in eukaryotic cells, the electron transport chain is located in or on the _____.

inner membrane of the mitochondrion

360

The overall efficiency of respiration (the percentage of the energy released that is saved in ATP) is approximately _____.

35%

361

Fermentation is essentially glycolysis plus an extra step in which pyruvate is reduced to form lactate or alcohol and carbon dioxide. This last step _____.

enables the cell to recycle the reduced NADH to oxidized NAD+

362

Sports physiologists at an Olympic training center wanted to monitor athletes to determine at what point their muscles were functioning anaerobically. They could do this by checking for a buildup of which of the following compounds?

lactate

363

In glycolysis in the absence of oxygen, cells need a way to regenerate which compound?

NAD+

364

Muscle tissues make lactate from pyruvate to do which of the following?

regenerate NAD+

365

In brewing beer, maltose (a disaccharide of glucose) is _____.

the substrate for alcoholic fermentation.

In alcoholic fermentation, maltose is cleaved into two glucose molecules, which undergo glycolysis. The resulting pyruvate is converted to ethanol in two steps, one of which regenerates the supply of NAD+ needed for continued glycolysis.

366

If muscle cells in the human body consume O2 faster than it can be supplied, which of the following is likely to result?

-The muscle cells will have more trouble making enough ATP to meet their energy requirements.
-The cells will not be able to carry out oxidative phosphorylation.
-The cells will consume glucose at an increased rate.

367

Of the metabolic pathways listed below, which is the only pathway found in all organisms?

glycolysis

368

When protein molecules are used as fuel for cellular respiration, _____ are produced as waste.

amino groups

369

A gram of fat oxidized by respiration produces approximately twice as much ATP as a gram of carbohydrate. Which of the following best explains this observation?

Fats are better electron donors to oxygen than are sugars.

370

If significant amounts of materials are removed from the citric acid cycle to produce amino acids for protein synthesis, which of the following will result?

-Less ATP will be produced by the cell.
-Less CO2 will be produced by the cell.
-The four-carbon compound that combines with acetyl CoA will have to be made by some other process.