OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

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In the second stage of protein synthesis, what happens to mRNA bases?

  1. They get attached to enzymes

  2. They pair with the exposed DNA bases

  3. They pair with other mRNA bases

  4. They are replaced with 'T'

The correct answer is: They pair with the exposed DNA bases

In the second stage of protein synthesis, known as transcription, mRNA bases are synthesized by pairing with the exposed DNA bases on the template strand of the DNA. This process ensures that the genetic code carried by the DNA is accurately transcribed into a complementary mRNA strand. Each base in the DNA pairs with its corresponding RNA base: adenine (A) pairs with uracil (U) in RNA (instead of thymine, which pairs with adenine in DNA), and cytosine (C) pairs with guanine (G). The result is a strand of mRNA that mirrors the DNA sequence, thus facilitating the subsequent process of translation, where the mRNA will guide protein synthesis. Other answer choices would not accurately describe the process. For instance, the idea of mRNA bases attaching to enzymes does not reflect the core role of mRNA during transcription. Likewise, pairing with other mRNA bases does not occur during this stage, as the mRNA strand is formed by directly complementing the DNA template. The notion of replacing mRNA bases with 'T' is incorrect because uracil (U) is used in RNA instead of thymine.

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