DNA Structure and Replication · USMLE Step 1

Which of the following correctly describes the directionality of new DNA strand synthesis by DNA polymerase?

  1. 5′ to 3′
  2. 3′ to 5′
  3. Either direction depending on strand
  4. Direction changes after RNA primer removal
Show answer and explanation

Correct answer: 5′ to 3′

DNA polymerases catalyze synthesis in the 5′→3′ direction, adding new nucleotides to the 3′-OH end of the growing strand.

Difficulty: Medium Question 9 of 20

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