MCAT Biochemistry Question 35: Answer and Explanation

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Question: 35

5. Hormones are found in the body in very low concentrations, but tend to have a strong effect. What type of receptor are hormones most likely to act on?

I. Ligand-gated ion channels

II. Enzyme-linked receptors

III. G protein-coupled receptors

  • A. I only
  • B. III only
  • C. II and III only
  • D. I, II, and III

Correct Answer: C

Explanation:

For a ligand present in low quantities to have a strong action, we expect it to initiate a second messenger cascade system. Second messenger systems amplify signals because enzymes can catalyze a reaction more than once while they are active, and often activate other enzymes. Both enzyme-linked receptors and G protein-coupled receptors use second messenger systems, while ion channels do not.

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