Question 1

Malate is both the starting and ending product of the citric acid cycle.

Accepted Answer

Malate is not the starting and ending product of the citric acid cycle. The starting product is acetyl-CoA and the ending products are ATP, CO2, and water. Malate is an intermediate product that is formed during the cycle.

Question 2

ATP is not generated directly in the citric acid cycle; instead, an intermediate is first generated by substrate-level phosphorylation. The intermediate is:

Accepted Answer

The intermediate generated by substrate-level phosphorylation in the citric acid cycle is GTP, which is then converted into ATP through the actions of nucleoside diphosphate kinase and adenylate kinase. Therefore, ATP is indirectly generated through the production of GTP.

Question 3

A research group has discovered an organism with cells that contain a previously undescribed organelle. They do some tests on the isolated organelle to see if it is involved in any major metabolic reactions. To do this, they incubate these organelles for a period of time and determine changes in the amount of various substances in the suspending solution. The results follow. $$\begin{array} { | l | l | l | l | l | } 
\hline \text { glucose } & \mathrm { CO } _ { 2 } & \mathrm { O } _ { 2 } & \mathrm { ATP } & \mathrm { NADH } \
\hline \text { no change } & \text { increase } & \text { no change } & \text { increase } & \text { increase } \
\hline
\end{array}$$ Based on this analysis, which metabolic process do you conclude is taking place in this organelle?

Accepted Answer

The increase in CO2, ATP, and NADH without a change in glucose or O2 levels suggests the citric acid cycle is occurring, as it produces these molecules without directly consuming glucose or oxygen.

Question 4

A research group has discovered an organism with cells that contain a previously undescribed organelle. They do some tests on the isolated organelle to see if it is involved in any major metabolic reactions. To do this, they incubate these organelles for a period of time and determine changes in the amount of various substances in the suspending solution. The results are: $$\begin{array} { | l | l | l | l | l | } 
\hline \text { glucose } & \mathrm { CO } _ { 2 } & \mathrm { O } _ { 2 } & \mathrm { ATP } & \text { NADH } \
\hline \text { decrease } & \text { no change } & \text { no change } & \text { increase } & \text { increase } \
\hline
\end{array}$$ Based on this analysis, which metabolic process do you conclude is taking place in this organelle?

Accepted Answer

The decrease in glucose and increase in ATP and NADH, without changes in CO2 or O2 levels, suggests glycolysis is occurring. Glycolysis breaks down glucose to produce ATP and NADH without requiring oxygen or producing CO2, distinguishing it from the citric acid cycle and oxidative phosphorylation, which involve changes in CO2 and O2.

Question 5

The pH in the intermembrane space of the mitochondria should be _____ compared with the matrix due to the concentration of protons in the intermembrane space.

Accepted Answer

The intermembrane space of the mitochondria should have a lower pH than the matrix due to the concentration of protons in the intermembrane space. This is because during the electron transport chain, protons are pumped from the matrix to the intermembrane space, creating a gradient. This gradient causes a higher concentration of protons in the intermembrane space, leading to a lower pH.

Question 6

Recall that the citric acid cycle starts with a four-carbon molecule, but that most of its intermediates are molecules that contain six carbons. How is this possible?

Accepted Answer

The citric acid cycle starts with the four-carbon molecule oxaloacetate combining with acetyl-CoA to form the six-carbon molecule citrate. Through a series of reactions, citrate is converted to isocitrate (six carbons), α-ketoglutarate (five carbons), succinyl-CoA (four carbons), succinate (four carbons), fumarate (four carbons), and finally malate (four carbons). The cycle is then completed when malate is converted back to oxaloacetate (four carbons), thus starting the process over again. Therefore, it is through the reaction of acetyl-CoA and oxaloacetate that the citric acid cycle intermediates gain two additional carbons.

Question 7

Oligomycin is an antibiotic that binds ATP synthase, blocking the flow of protons through the enzyme's proton channel. In addition to preventing synthesis of ATP, what additional effect might you expect in response to the presence of oligomycin?

Accepted Answer

Oligomycin blocks the flow of protons through the proton channel of ATP synthase, which increases the proton gradient across the inner mitochondrial membrane. This leads to a decrease in pH in the intermembrane space, as protons accumulate there due to the inability to flow through ATP synthase.

Question 8

Brown fat is a specialized tissue found in infants and hibernating mammals. Brown fat mitochondria have proton channels located in their inner membranes. What does this mean for the organism?

Accepted Answer

The proton channels in the inner membrane of brown fat mitochondria contribute to the formation of a proton electrochemical gradient. The potential energy of this gradient is then released as heat, which helps to maintain body temperature in infants and hibernating mammals. Therefore, choice C is the best answer. Choices A, B, and D are incorrect.

Question 9

A researcher is studying a population of bacteria that carry out the citric acid cycle, but do so in reverse. What statements are likely TRUE of these bacteria?

Accepted Answer

Bacteria that carry out the citric acid cycle in reverse are called anaplerotic bacteria. They use the cycle to produce intermediates that can be used to synthesize sugars and other biomolecules. They do not carry out cellular respiration in their mitochondria and do not release CO₂ as a waste product. Option A is incorrect because these bacteria use the reversed citric acid cycle to produce intermediates, not energy. Option E is incorrect because these bacteria do not have mitochondria.

Question 10

A single molecule of glucose requires _____ "turn(s)" through the citric acid cycle for its chemical energy to be completely harvested.

Accepted Answer

A single molecule of glucose enters the citric acid cycle as two molecules of acetyl-CoA, which then goes through a series of reactions that generate energy in the form of ATP, NADH, and FADH2. It takes two turns through the citric acid cycle (one turn for each acetyl-CoA molecule) to completely harvest the energy from a molecule of glucose. Therefore, the answer is B - 2 turns.

Question 11

During the citric acid cycle, the production of CO₂ is the result of the _____ of intermediate compounds of the citric acid cycle coupled to the production of _____.

Accepted Answer

The production of CO2 during the citric acid cycle is the result of the oxidation of intermediate compounds, which is coupled to the production of NADH. This process involves the transfer of electrons to NAD+, forming NADH.

Question 12

Which of the following processes produces the HIGHEST number of reduced electron carriers and thus the GREATEST amount of ATP by oxidative phosphorylation?

Accepted Answer

The citric acid cycle produces the highest number of reduced electron carriers (NADH and FADH2), which go on to generate ATP through oxidative phosphorylation in the electron transport chain. Glycolysis produces a smaller number of reduced electron carriers, and pyruvate oxidation only produces a single NADH molecule. Therefore, the citric acid cycle is the most efficient process for ATP production through oxidative phosphorylation.

Question 13

A research group has discovered an organism with cells that contain a previously undescribed organelle. They do some tests on the isolated organelle to see if it is involved in any major metabolic reactions. To do this, they incubate these organelles for a period of time and determine changes in the amount of various substances in the suspending solution. The results follow. $$\begin{array} { | l | l | l | l | l | } 
\hline \text { glucose } & \mathrm { CO } _ { 2 } & \mathrm { O } _ { 2 } & \mathrm { ATP } & \mathrm { NADH } \
\hline \text { no change } & \text { no change } & \text { decrease } & \text { increase } & \text { decrease } \
\hline
\end{array}$$ Based on this analysis, which metabolic process do you conclude is taking place in this organelle?

Accepted Answer

The decrease in O2 and NADH, along with an increase in ATP, indicates that the organelle is involved in the electron transport chain/oxidative phosphorylation, where oxygen is used as the final electron acceptor, and ATP is generated.

Question 14

Which of these reactions summarizes the overall reactions of cellular respiration?

Accepted Answer

The correct reaction for cellular respiration is glucose (C6H12O6) combining with oxygen (O2) to produce carbon dioxide (CO2), water (H2O), and energy. This is represented in choice A, despite the formatting issues.

Question 15

Atractyloside is a poison that inhibits the transport of ADP from the cytosol across the mitochondrial membranes and into the mitochondrial matrix. The direct effect of this drug is to stop ATP synthesis because:

Accepted Answer

ADP is a necessary substrate for the reaction catalyzed by ATP synthase. Without ADP, ATP cannot be synthesized.

Question 16

Once they have been processed through the citric acid cycle, the acetyl-CoA molecules from a single glucose molecule produce:

Accepted Answer

From a single glucose molecule, two molecules of acetyl-CoA are generated, which enter the citric acid cycle. For each acetyl-CoA molecule processed, the cycle produces 3 NADH, 1 FADH2, 1 ATP (or GTP), and 2 CO2. Therefore, for two acetyl-CoA molecules, this doubles to 6 NADH, 2 FADH2, 2 ATP (or GTP), and 4 CO2.

Question 17

Which is the ONLY reaction in the citric acid cycle that produces ATP by substrate-level phosphorylation?

Accepted Answer

The only reaction in the citric acid cycle that produces ATP by substrate-level phosphorylation is the conversion of succinyl-CoA to succinate by the enzyme succinyl-CoA synthetase, which generates GTP that can be converted to ATP.

Question 18

Which of the following is NOT an end product for an acetyl group that enters the citric acid cycle?

Accepted Answer

The citric acid cycle (also known as the Krebs cycle or TCA cycle) primarily generates ATP, NADH, and FADH2 as end products through a series of enzymatic reactions. These molecules are crucial for cellular energy production and electron transport chain function. Oxaloacetate, however, is not an end product but rather a reactant that combines with acetyl-CoA to begin the cycle, eventually being regenerated to sustain the cycle's continuity.

Question 19

Imagine that you exhale after a deep breath. Which of the following are you NOT exhaling?

Accepted Answer

Glycolysis occurs in the cytoplasm and does not produce gaseous waste products like CO2, which are exhaled.

Question 20

Very low concentrations of detergent make membranes leaky to small molecules and ions without damaging proteins. In isolated mitochondria exposed to detergent, the molecules of the electron transport chain and of ATP synthase remain intact. Do you expect ATP synthesis to continue in the presence of low concentrations of detergent?

Accepted Answer

ATP synthesis depends on the maintenance of a proton gradient across the mitochondrial inner membrane. A leaky membrane would allow protons to leak back into the matrix, preventing the establishment of a proton gradient necessary for ATP synthesis.

Quiz 7: Cellular Respiration: Harvesting Energy From Carbohydrates and Other Fuel Molecules

Malate is both the starting and ending product of the citric acid cycle.

ATP is not generated directly in the citric acid cycle; instead, an intermediate is first generated by substrate-level phosphorylation. The intermediate is:

The pH in the intermembrane space of the mitochondria should be _____ compared with the matrix due to the concentration of protons in the intermembrane space.

Recall that the citric acid cycle starts with a four-carbon molecule, but that most of its intermediates are molecules that contain six carbons. How is this possible?

Oligomycin is an antibiotic that binds ATP synthase, blocking the flow of protons through the enzyme's proton channel. In addition to preventing synthesis of ATP, what additional effect might you expect in response to the presence of oligomycin?

Brown fat is a specialized tissue found in infants and hibernating mammals. Brown fat mitochondria have proton channels located in their inner membranes. What does this mean for the organism?

A researcher is studying a population of bacteria that carry out the citric acid cycle, but do so in reverse. What statements are likely TRUE of these bacteria?

A single molecule of glucose requires _____ "turn(s) " through the citric acid cycle for its chemical energy to be completely harvested.

During the citric acid cycle, the production of CO₂ is the result of the _ of intermediate compounds of the citric acid cycle coupled to the production of _.

Which of the following processes produces the HIGHEST number of reduced electron carriers and thus the GREATEST amount of ATP by oxidative phosphorylation?

Which of these reactions summarizes the overall reactions of cellular respiration?

Atractyloside is a poison that inhibits the transport of ADP from the cytosol across the mitochondrial membranes and into the mitochondrial matrix. The direct effect of this drug is to stop ATP synthesis because:

Once they have been processed through the citric acid cycle, the acetyl-CoA molecules from a single glucose molecule produce:

Which is the ONLY reaction in the citric acid cycle that produces ATP by substrate-level phosphorylation?

Which of the following is NOT an end product for an acetyl group that enters the citric acid cycle?

Imagine that you exhale after a deep breath. Which of the following are you NOT exhaling?

Quiz 7: Cellular Respiration: Harvesting Energy From Carbohydrates and Other Fuel Molecules

Malate is both the starting and ending product of the citric acid cycle.

ATP is not generated directly in the citric acid cycle; instead, an intermediate is first generated by substrate-level phosphorylation. The intermediate is:

The pH in the intermembrane space of the mitochondria should be _____ compared with the matrix due to the concentration of protons in the intermembrane space.

Recall that the citric acid cycle starts with a four-carbon molecule, but that most of its intermediates are molecules that contain six carbons. How is this possible?

Oligomycin is an antibiotic that binds ATP synthase, blocking the flow of protons through the enzyme's proton channel. In addition to preventing synthesis of ATP, what additional effect might you expect in response to the presence of oligomycin?

Brown fat is a specialized tissue found in infants and hibernating mammals. Brown fat mitochondria have proton channels located in their inner membranes. What does this mean for the organism?

A researcher is studying a population of bacteria that carry out the citric acid cycle, but do so in reverse. What statements are likely TRUE of these bacteria?

A single molecule of glucose requires _____ "turn(s) " through the citric acid cycle for its chemical energy to be completely harvested.

During the citric acid cycle, the production of CO2 is the result of the _____ of intermediate compounds of the citric acid cycle coupled to the production of _____.

Which of the following processes produces the HIGHEST number of reduced electron carriers and thus the GREATEST amount of ATP by oxidative phosphorylation?

Which of these reactions summarizes the overall reactions of cellular respiration?

Atractyloside is a poison that inhibits the transport of ADP from the cytosol across the mitochondrial membranes and into the mitochondrial matrix. The direct effect of this drug is to stop ATP synthesis because:

Once they have been processed through the citric acid cycle, the acetyl-CoA molecules from a single glucose molecule produce:

Which is the ONLY reaction in the citric acid cycle that produces ATP by substrate-level phosphorylation?

Which of the following is NOT an end product for an acetyl group that enters the citric acid cycle?

Imagine that you exhale after a deep breath. Which of the following are you NOT exhaling?

During the citric acid cycle, the production of CO₂ is the result of the _ of intermediate compounds of the citric acid cycle coupled to the production of _.