Question 1

In step 6 of the citric acid cycle, succinate + FAD $\rightarrow$ fumarate + FADH_2. Which statement concerning this reaction is/are TRUE?

Accepted Answer

Fumarate is more oxidized than succinate as it loses electrons, and FAD acts as an oxidizing agent by accepting electrons and becoming FADH2.

Question 2

Which of the following statements is true regarding pyruvate oxidation?

Accepted Answer

Pyruvate oxidation occurs in the matrix of mitochondria, is indeed the second stage of cellular respiration, produces both CO2 and acetyl-CoA, and does not yield ATP via substrate-level phosphorylation, making all the provided statements correct.

Question 3

The citric acid cycle begins when acetyl-CoA combines with _____ to form _____.

Accepted Answer

The citric acid cycle begins when acetyl-CoA combines with oxaloacetate to form citrate. This is the first step of the cycle and is catalyzed by the enzyme citrate synthase. Choice A is incorrect because pyruvate is not a part of the citric acid cycle. Choice B is incorrect because malate is not involved in the initial step of the cycle. Choice C is incorrect because it describes a step that occurs later in the cycle. Choice E is incorrect because cis-aconitate is an intermediate, not a starting compound.

Question 4

The majority of the energy generated in the citric acid cycle is in the form of:

Accepted Answer

The majority of the energy generated in the citric acid cycle is in the form of electrons donated to NAD+ and FAD, which are then used in the electron transport chain to generate ATP through oxidative phosphorylation.

Question 5

If an energy source such as sunlight is available, the citric acid cycle can run in reverse in some organisms.

Accepted Answer

This process is known as the reverse citric acid cycle or the reductive TCA cycle and occurs in some photosynthetic bacteria and archaea. The process involves using energy from sunlight to convert carbon dioxide into organic compounds through the reverse citric acid cycle.

Question 6

Order the following list of molecules according to their potential energy from high to low. A. ATP B. NADH C. NAD⁺ D. FADH₂

Accepted Answer

The answer of Order the following list of molecules according...

Question 7

The citric acid cycle is a cycle because the starting molecule, _____, is regenerated at the end.

Accepted Answer

Oxaloacetate is the starting molecule of the citric acid cycle and is regenerated at the end of the cycle, making it a cycle.

Question 8

Which of the following is a net product of the citric acid cycle for each molecule of pyruvate generated in glycolysis?

Accepted Answer

The answer of Which of the following is a net...

Question 9

Complete oxidation of glucose to CO₂involves two different mechanisms for synthesizing ATP: oxidative phosphorylation and substrate-level phosphorylation. Substrate-level phosphorylation:

Accepted Answer

The answer of Complete oxidation of glucose to CO₂involves...

Question 10

Each round of the citric acid cycle begins when the four-carbon molecule oxaloacetate is converted to the six-carbon molecule citrate. As the cycle progresses, two carbons are eliminated to regenerate the oxaloacetate. The added carbon is supplied by _____ and the two eliminated carbons are released as _____.

Accepted Answer

The added carbon comes from acetyl-CoA, which combines with oxaloacetate to form citrate. As the cycle progresses, two carbons are released as carbon dioxide (CO2).

Question 11

Pyruvate can be used to produce:

Accepted Answer

The answer of Pyruvate can be used to produce:
...

Question 12

During the citric acid cycle:

Accepted Answer

During the citric acid cycle, ATP is synthesized by substrate-level phosphorylation, which is a direct transfer of a phosphate group to ADP from an intermediate.

Question 13

In which stage of cellular respiration is the greatest amount of chemical energy harvested from molecules that are derived from food?

Accepted Answer

The answer of In which stage of cellular respiration is...

Question 14

The citric acid cycle is believed to have developed fairly recently in the evolution of cellular life.

Accepted Answer

The citric acid cycle, also known as the Krebs cycle or the tricarboxylic acid cycle, is a central metabolic pathway found in most living organisms, including bacteria and eukaryotes. It is believed to have evolved very early in the history of life, possibly before the emergence of oxygen-producing photosynthesis.

Question 15

Which of the following molecules has the GREATEST potential energy?

Accepted Answer

ATP has the greatest potential energy because it has three phosphate groups, which can be broken down to release energy.

Question 16

In 1937, two German biochemists published a paper proposing the following reactions as part of glucose oxidation: citrate $\rightarrow$ isocitrate $\rightarrow$$\alpha$-ketoglutarate $\rightarrow$succinate $\rightarrow$ fumarate $\rightarrow$malate $\rightarrow$oxaloacetate
Adding succinate, fumarate, or malate to thin slices of tissue increased oxygen consumption, supporting the hypothesis that these molecules are intermediates in the process. However, a puzzling observation was that intermediates were still present in the reaction mixture at the end of the experiment. If they are intermediates, then they should be consumed as the next product in the pathway is formed. What explains this observation?

Accepted Answer

The intermediates succinate, fumarate, and malate are constantly regenerated in the citric acid pathway, therefore they are still present in the reaction mixture at the end of the experiment.

Question 17

Following the citric acid cycle but before the electron transport chain and oxidative phosphorylation, how much potential energy has been transferred to the bonds of ATP (at 7.3 kcal/mol)? the bonds of NADH (at 53 kcal/mol)? If glucose oxidation to CO₂ and H₂O has a $\Delta$G of 676 kcal/mol, what proportion of potential energy has been captured? Where would you predict the remaining potential energy has gone?

Accepted Answer

The answer of Following the citric acid cycle but before...

Question 18

Acetate is the starting point for synthesis of a cell's _____.

Accepted Answer

The answer of Acetate is the starting point for synthesis...

Question 19

Following the citric acid cycle but before the electron transport chain and oxidative phosphorylation, most of the energy from the original glucose molecule is found in:

Accepted Answer

The NADH produced in the citric acid cycle carries most of the energy from the original glucose molecule. This NADH will then be used in the electron transport chain and oxidative phosphorylation to produce ATP.

Question 20

The citric acid cycle takes place in the:

Accepted Answer

The citric acid cycle, also known as the Krebs cycle, occurs in the mitochondrial matrix. This is where the enzymes and cofactors involved in the cycle are located, and where the reactions take place. The other options listed are not correct, as they do not correspond to the location of the citric acid cycle.

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

In step 6 of the citric acid cycle, succinate + FAD $\rightarrow$ fumarate + FADH_2. Which statement concerning this reaction is/are TRUE?

Which of the following statements is true regarding pyruvate oxidation?

The citric acid cycle begins when acetyl-CoA combines with _ to form _.

The majority of the energy generated in the citric acid cycle is in the form of:

If an energy source such as sunlight is available, the citric acid cycle can run in reverse in some organisms.

Order the following list of molecules according to their potential energy from high to low. A. ATP B. NADH C. NAD⁺ D. FADH₂

The citric acid cycle is a cycle because the starting molecule, _____, is regenerated at the end.

Which of the following is a net product of the citric acid cycle for each molecule of pyruvate generated in glycolysis?

Complete oxidation of glucose to CO₂involves two different mechanisms for synthesizing ATP: oxidative phosphorylation and substrate-level phosphorylation. Substrate-level phosphorylation:

Pyruvate can be used to produce:

During the citric acid cycle:

In which stage of cellular respiration is the greatest amount of chemical energy harvested from molecules that are derived from food?

The citric acid cycle is believed to have developed fairly recently in the evolution of cellular life.

Which of the following molecules has the GREATEST potential energy?

Acetate is the starting point for synthesis of a cell's _____.

Following the citric acid cycle but before the electron transport chain and oxidative phosphorylation, most of the energy from the original glucose molecule is found in:

The citric acid cycle takes place in the:

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

In step 6 of the citric acid cycle, succinate + FAD →\rightarrow→ fumarate + FADH2. Which statement concerning this reaction is/are TRUE?

Which of the following statements is true regarding pyruvate oxidation?

The citric acid cycle begins when acetyl-CoA combines with _____ to form _____.

The majority of the energy generated in the citric acid cycle is in the form of:

If an energy source such as sunlight is available, the citric acid cycle can run in reverse in some organisms.

Order the following list of molecules according to their potential energy from high to low. A. ATP B. NADH C. NAD+ D. FADH2

The citric acid cycle is a cycle because the starting molecule, _____, is regenerated at the end.

Which of the following is a net product of the citric acid cycle for each molecule of pyruvate generated in glycolysis?

Complete oxidation of glucose to CO2 involves two different mechanisms for synthesizing ATP: oxidative phosphorylation and substrate-level phosphorylation. Substrate-level phosphorylation:

Pyruvate can be used to produce:

During the citric acid cycle:

In which stage of cellular respiration is the greatest amount of chemical energy harvested from molecules that are derived from food?

The citric acid cycle is believed to have developed fairly recently in the evolution of cellular life.

Which of the following molecules has the GREATEST potential energy?

Acetate is the starting point for synthesis of a cell's _____.

Following the citric acid cycle but before the electron transport chain and oxidative phosphorylation, most of the energy from the original glucose molecule is found in:

The citric acid cycle takes place in the:

In step 6 of the citric acid cycle, succinate + FAD $\rightarrow$ fumarate + FADH_2. Which statement concerning this reaction is/are TRUE?

The citric acid cycle begins when acetyl-CoA combines with _ to form _.

Order the following list of molecules according to their potential energy from high to low. A. ATP B. NADH C. NAD⁺ D. FADH₂

Complete oxidation of glucose to CO₂involves two different mechanisms for synthesizing ATP: oxidative phosphorylation and substrate-level phosphorylation. Substrate-level phosphorylation: