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

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Which base is replaced with 'U' in mRNA?

  1. A

  2. T

  3. C

  4. G

The correct answer is: T

In the process of transcription, the base thymine (T) found in DNA is replaced with uracil (U) in messenger RNA (mRNA). This substitution occurs because uracil serves a similar function as thymine, pairing with adenine (A) during the synthesis of RNA. In DNA, thymine is one of the four nucleobases, while RNA contains uracil instead of thymine. This difference is crucial in the formation of RNA, as it allows the correct pairing of bases and maintains the fidelity of the genetic code during protein synthesis. Understanding this substitution is fundamental in genetics and molecular biology, as it helps facilitate the transcription of genetic information from DNA to RNA, ultimately leading to protein synthesis.

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