MCAT Biochemistry Question 77: Answer and Explanation

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Question: 77

2. Which of the following statements regarding differences between DNA and RNA is FALSE?

  • A. DNA is double-stranded, whereas RNA is single-stranded.
  • B. DNA uses the nitrogenous base thymine; RNA uses uracil.
  • C. The sugar in DNA is deoxyribose; the sugar in RNA is ribose.
  • D. DNA strands replicate in a 5′ to 3′ direction, whereas RNA is synthesized in a 3′ to 5′ direction.

Correct Answer: D

Explanation:

Because we are looking for the false statement, we have to read each choice to eliminate those that are true or find one that is overtly false. Let’s quickly review the main differences between DNA and RNA. DNA is double-stranded, with a deoxyribose sugar and the nitrogenous bases A, T, C, and G. RNA, on the other hand, is usually single-stranded, with a ribose sugar and the bases A, U, C, and G. Choice (D) is false because both DNA replication and RNA synthesis proceed in a 5′ to 3′ direction.

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