In the presence of oxygen, the three-carbon compound pyruvate can be catabolized in the citric acid cycle. First, however, the pyruvate (1) loses a carbon, which is given off as a molecule of CO2, (2) is oxidized to form a two-carbon compound called acetate, and (3) is bonded to coenzyme A. Why is coenzyme A, a sulfur-containing molecule derived from a B vitamin, added?

In the presence of oxygen, the three-carbon compound pyruvate can be catabolized in the citric acid cycle. First, however, the pyruvate (1) loses a carbon, which is given off as a molecule of CO2, (2) is oxidized to form a two-carbon compound called acetate, and (3) is bonded to coenzyme A.
Why is coenzyme A, a sulfur-containing molecule derived from a B vitamin, added? 

A) because sulfur is needed for the molecule to enter the mitochondrion
B) in order to utilize this portion of a B vitamin which would otherwise be a waste product from another pathway
C) to provide a relatively unstable molecule whose acetyl portion can be readily transferred to a compound in the citric acid cycle
D) because it drives the reaction that regenerates NAD?
E) in order to remove one molecule of CO2






Answer: C

In the presence of oxygen, the three-carbon compound pyruvate can be catabolized in the citric acid cycle. First, however, the pyruvate (1) loses a carbon, which is given off as a molecule of CO2, (2) is oxidized to form a two-carbon compound called acetate, and (3) is bonded to coenzyme A. These three steps result in the formation of

In the presence of oxygen, the three-carbon compound pyruvate can be catabolized in the citric acid cycle. First, however, the pyruvate (1) loses a carbon, which is given off as a molecule of CO2, (2) is oxidized to form a two-carbon compound called acetate, and (3) is bonded to coenzyme A.
These three steps result in the formation of 

A) acetyl CoA, O2, and ATP.
B) acetyl CoA, FADH2, and CO2.
C) acetyl CoA, FAD, H2, and CO2.
D) acetyl CoA, NADH, H?, and CO2.
E) acetyl CoA, NAD?, ATP, and CO2.






Answer: D

Yeast cells that have defective mitochondria incapable of respiration will be able to grow by catabolizing which of the following carbon sources for energy?

Yeast cells that have defective mitochondria incapable of respiration will be able to grow by catabolizing which of the following carbon sources for energy? 

A) glucose
B) proteins
C) fatty acids
D) glucose, proteins, and fatty acids
E) Such yeast cells will not be capable of catabolizing any food molecules, and will therefore die.







Answer: A

During intense exercise, as skeletal muscle cells go into anaerobiosis, the human body will increase its catabolism of

During intense exercise, as skeletal muscle cells go into anaerobiosis, the human body will increase its catabolism of 

A) fats only.
B) carbohydrates only.
C) proteins only.
D) fats, carbohydrates, and proteins.
E) fats and proteins only.







Answer: B

High levels of citric acid inhibit the enzyme phosphofructokinase, a key enzyme in glycolysis. Citric acid binds to the enzyme at a different location from the active site. This is an example of

High levels of citric acid inhibit the enzyme phosphofructokinase, a key enzyme in glycolysis. Citric acid binds to the enzyme at a different location from the active site. This is an example of 

A) competitive inhibition.
B) allosteric regulation.
C) the specificity of enzymes for their substrates.
D) an enzyme requiring a cofactor.
E) positive feedback regulation.




Answer: B

What carbon sources can yeast cells metabolize to make ATP from ADP under anaerobic conditions?

What carbon sources can yeast cells metabolize to make ATP from ADP under anaerobic conditions?

A) glucose
B) ethanol
C) pyruvate
D) lactic acid
E) either ethanol or lactic acid






Answer: A

Where do the catabolic products of fatty acid breakdown enter into the citric acid cycle?

Where do the catabolic products of fatty acid breakdown enter into the citric acid cycle? 

A) pyruvate
B) malate or fumarate
C) acetyl CoA
D) a-ketoglutarate
E) succinyl CoA






Answer: C

What is the purpose of beta oxidation in respiration?

What is the purpose of beta oxidation in respiration? 

A) oxidation of glucose
B) oxidation of pyruvate
C) feedback regulation
D) control of ATP accumulation
E) breakdown of fatty acids








Answer: E

In vertebrate animals, brown fat tissue's color is due to abundant blood vessels and capillaries. White fat tissue, on the other hand, is specialized for fat storage and contains relatively few blood vessels or capillaries. Brown fat cells have a specialized protein that dissipates the proton-motive force across the mitochondrial membranes. Which of the following might be the function of the brown fat tissue?

In vertebrate animals, brown fat tissue's color is due to abundant blood vessels and capillaries. White fat tissue, on the other hand, is specialized for fat storage and contains relatively few blood vessels or capillaries. Brown fat cells have a specialized protein that dissipates the proton-motive force across the mitochondrial membranes. Which of the following might be the function of the brown fat tissue? 

A) to increase the rate of oxidative phosphorylation from its few mitochondria
B) to allow the animals to regulate their metabolic rate when it is especially hot
C) to increase the production of ATP
D) to allow other membranes of the cell to perform mitochondrial functions
E) to regulate temperature by converting most of the energy from NADH oxidation to heat






Answer: E

Even though plants carry on photosynthesis, plant cells still use their mitochondria for oxidation of pyruvate. When and where will this occur?

Even though plants carry on photosynthesis, plant cells still use their mitochondria for oxidation of pyruvate. When and where will this occur? 

A) in photosynthetic cells in the light, while photosynthesis occurs concurrently
B) in nonphotosynthesizing cells only
C) in cells that are storing glucose only
D) in all cells all the time
E) in photosynthesizing cells in the light and in other tissues in the dark







Answer: D

Phosphofructokinase is an allosteric enzyme that catalyzes the conversion of fructose 6-phosphate to fructose 1,6-bisphosphate, an early step of glycolysis. In the presence of oxygen, an increase in the amount of ATP in a cell would be expected to

Phosphofructokinase is an allosteric enzyme that catalyzes the conversion of fructose 6-phosphate to fructose 1,6-bisphosphate, an early step of glycolysis. In the presence of oxygen, an increase in the amount of ATP in a cell would be expected to 

A) inhibit the enzyme and thus slow the rates of glycolysis and the citric acid cycle.
B) activate the enzyme and thus slow the rates of glycolysis and the citric acid cycle.
C) inhibit the enzyme and thus increase the rates of glycolysis and the citric acid cycle.
D) activate the enzyme and increase the rates of glycolysis and the citric acid cycle.
E) inhibit the enzyme and thus increase the rate of glycolysis and the concentration of citrate.







Answer: A

Phosphofructokinase is an important control enzyme in the regulation of cellular respiration. Which of the following statements correctly describes phosphofructokinase activity?

Phosphofructokinase is an important control enzyme in the regulation of cellular respiration. Which of the following statements correctly describes phosphofructokinase activity? 

A) It is inhibited by AMP.
B) It is activated by ATP.
C) It is activated by citrate, an intermediate of the citric acid cycle.
D) It catalyzes the conversion of fructose 1,6-bisphosphate to fructose 6-phosphate, an early step of glycolysis.
E) It is an allosteric enzyme.






Answer: E

You have a friend who lost 7 kg (about 15 pounds) of fat on a regimen of strict diet and exercise. How did the fat leave her body?

You have a friend who lost 7 kg (about 15 pounds) of fat on a regimen of strict diet and exercise. How did the fat leave her body? 

A) It was released as CO2 and H2O.
B) It was converted to heat and then released.
C) It was converted to ATP, which weighs much less than fat.
D) It was broken down to amino acids and eliminated from the body.
E) It was converted to urine and eliminated from the body.






Answer: A

A mutation in yeast makes it unable to convert pyruvate to ethanol. How will this mutation affect these yeast cells?

A mutation in yeast makes it unable to convert pyruvate to ethanol. How will this mutation affect these yeast cells? 

A) The mutant yeast will be unable to grow anaerobically.
B) The mutant yeast will grow anaerobically only when given glucose.
C) The mutant yeast will be unable to metabolize glucose.
D) The mutant yeast will die because they cannot regenerate NAD? from NAD.
E) The mutant yeast will metabolize only fatty acids.





Answer: A

When skeletal muscle cells undergo anaerobic respiration, they become fatigued and painful. This is now known to be caused by

When skeletal muscle cells undergo anaerobic respiration, they become fatigued and painful. This is now known to be caused by 

A) buildup of pyruvate.
B) buildup of lactate.
C) increase in sodium ions.
D) increase in potassium ions.
E) increase in ethanol.







Answer: B

When skeletal muscle cells are oxygen-deprived, the heart still pumps. What must the heart muscle cells be able to do?

When skeletal muscle cells are oxygen-deprived, the heart still pumps. What must the heart muscle cells be able to do? 

A) derive sufficient energy from fermentation
B) continue aerobic metabolism when skeletal muscle cannot
C) transform lactate to pyruvate again
D) remove lactate from the blood
E) remove oxygen from lactate






Answer: B

When an individual is exercising heavily and when the muscle becomes oxygen-deprived, muscle cells convert pyruvate to lactate. What happens to the lactate in skeletal muscle cells?

When an individual is exercising heavily and when the muscle becomes oxygen-deprived, muscle cells convert pyruvate to lactate. What happens to the lactate in skeletal muscle cells? 

A) It is converted to NAD?.
B) It produces CO2 and water.
C) It is taken to the liver and converted back to pyruvate.
D) It reduces FADH2 to FAD?.
E) It is converted to alcohol.







Answer: C

Why is glycolysis considered to be one of the first metabolic pathways to have evolved?

Why is glycolysis considered to be one of the first metabolic pathways to have evolved? 

A) It produces much less ATP than does oxidative phosphorylation.
B) It does not involve organelles or specialized structures, does not require oxygen, and is present in most organisms.
C) It is found in prokaryotic cells but not in eukaryotic cells.
D) It relies on chemiosmosis, which is a metabolic mechanism present only in the first cells' prokaryotic cells.
E) It requires the presence of membrane-enclosed cell organelles found only in eukaryotic cells.







Answer: B

Which statement best supports the hypothesis that glycolysis is an ancient metabolic pathway that originated before the last universal common ancestor of life on Earth?

Which statement best supports the hypothesis that glycolysis is an ancient metabolic pathway that originated before the last universal common ancestor of life on Earth?

A) Glycolysis is widespread and is found in the domains Bacteria, Archaea, and Eukarya.
B) Glycolysis neither uses nor needs O2.
C) Glycolysis is found in all eukaryotic cells.
D) The enzymes of glycolysis are found in the cytosol rather than in a membrane-enclosed organelle.
E) Ancient prokaryotic cells, the most primitive of cells, made extensive use of glycolysis long before oxygen was present in Earth's atmosphere.







Answer: A

An organism is discovered that thrives both in the presence and absence of oxygen in the air. Curiously, the consumption of sugar increases as oxygen is removed from the organism's environment, even though the organism does not gain much weight. This organism

An organism is discovered that thrives both in the presence and absence of oxygen in the air. Curiously, the consumption of sugar increases as oxygen is removed from the organism's environment, even though the organism does not gain much weight. This organism 

A) must use a molecule other than oxygen to accept electrons from the electron transport chain.
B) is a normal eukaryotic organism.
C) is photosynthetic.
D) is an anaerobic organism.
E) is a facultative anaerobe.








Answer: E