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Straight from the Progress Note question bank, each with a cited explanation. No account needed.
Coenzyme A (CoA) plays a central role in metabolism, most familiarly as acetyl-CoA. What is its primary function?
Answer: E. Coenzyme A is a coenzyme whose reactive thiol (–SH) group forms high-energy thioester bonds with acyl groups, letting it carry and transfer those groups — most notably as acetyl-CoA — between metabolic reactions, for example delivering the two-carbon acetyl unit from pyruvate oxidation into the citric acid cycle. A describes nucleic acids, B describes ATP synthase, C describes hemoglobin, and D describes phospholipids, none of which is CoA's role. Carrying and transferring acyl groups such as acetyl is coenzyme A's central function.
A student adds a catalyst to a reaction mixture. Which thermodynamic and kinetic parameters are immediately affected?
Answer: C. Catalysts lower activation energy by stabilizing the transition state, increasing reaction rate. They do not alter ΔG° and therefore do not change equilibrium position. This distinction is central to catalytic function.
In a DNA double helix, the two strands are described as 'antiparallel.' What does this mean?
Answer: E. 'Antiparallel' means the two strands of the double helix run in opposite directions: one is oriented 5'→3' while its complementary partner runs 3'→5'. A is wrong because the strands are complementary, not identical, and B has both strands parallel, which they are not. C misstates the bonding (the strands are held together by hydrogen bonds, not covalent bonds), and D contradicts the need to break hydrogen bonds to separate them; opposite 5'/3' orientation is what antiparallel means.
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