In the Presence of Oxygen, the Three-Carbon Compound Pyruvate Can

question 98

Multiple Choice

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

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Definitions:

Element

A substance that cannot be changed to a simpler substance by a normal chemical reaction.

Neutrons

Subatomic particles without an electric charge, found in the nucleus of an atom, contributing to the atom's mass.

Electrons

subatomic particles with a negative charge, found in all atoms and acting as the primary carrier of electricity in solids.

Valence Shells

The outermost electron shell of an atom that determines its bonding behavior with other atoms.