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