Chapter 8 & 9 (Questions) Flashcards
1
Q
The process of cellular respiration, which converts simple sugars such as glucose into CO2 and water, is an example of _____.
A
a catabolic pathway
2
Q
Cellular respiration is a
A
catabolic pathway
3
Q
Energy is observed in two basic forms: potential and kinetic. Which of the following correctly matches these forms with a source of energy?
A
the covalent bonds of a sugar molecule: potential energy.
4
Q
Bonds are a form of potential energy because the energy
A
arises from the relative positions of the atoms that form the bond.
5
Q
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?
A
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
Q
Which of the following statements about equilibrium of chemical reactions is correct?
A
A reactions that is at equilibrium is not capable of doing any work.
7
Q
The ΔG for a reaction at equilibrium is zero, which means that
A
there is no free energy available to do any work.
8
Q
Which of the following statements about ATP (adenosine triphosphate) is correct?
A
The cycling between ATP and ADP + Pi provides an energy coupling between catabolic and anabolic pathways.
9
Q
Catabolic pathways provide the energy needed to make ATP from ADP and Pi. The hydrolysis of
A
ATP to ADP + Pi releases the same amount of energy.
10
Q
Enzymes are described as catalysts, which means that they _____.
A
increase the rate of a reaction without being consumed by the reaction.
This permits enzyme molecules to be used repeatedly.
11
Q
Which of the following would be unlikely to contribute to the substrate specificity of an enzyme?
A
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
Q
Which of the following would be likely to contribute to the substrate specificity of an enzyme?
A
- 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
Q
Which of the following is NOT a way in which an enzyme can speed up the reaction that it catalyzes?
A
The active site can provide heat from the environment that raises the energy content of the substrate.
14
Q
Which of the following are ways in which an enzyme can speed up the reaction that it catalyzes?
A
- 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
Q
An enzyme cannot extract heat from the environment to speed a reaction. It can only
A
lower the activation energy barrier so that more substrates have the energy to react.
16
Q
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?
A
The compound is a competitive inhibitor.
17
Q
A competitive inhibitor slows down the enzyme by competing with the
A
substrate for binding at the active site. Increasing substrate concentrations will reduce the effectiveness of a competitive inhibitor.
18
Q
Which of the following statements about feedback regulation of a metabolic pathway is correct?
A
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
Q
Which of these is exhibiting kinetic energy?
A
a space station orbiting Earth.
20
Q
Kinetic energy is
A
energy of motion.
21
Q
“Conservation of energy” refers to the fact that _____.
A
energy cannot be created or destroyed but can be converted from one form to another
22
Q
Chemical energy is a form of _____ energy.
A
potential
23
Q
Chemical energy is a form of
A
stored energy.
24
Q
In your body, what process converts the chemical energy found in glucose into the chemical energy found in ATP?
A
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.
