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

What happens during stage 3 of protein synthesis?

1. The ribosome attaches to the DNA strand

2. The mRNA peels off from the DNA

3. Free amino acids bind to the ribosome

4. The DNA strands rejoin

The correct answer is: The mRNA peels off from the DNA

During stage 3 of protein synthesis, the correct process involves the mRNA peeling off from the DNA. This stage follows transcription, where the DNA is first transcribed to produce mRNA. Once the mRNA molecule is synthesized, it detaches from the DNA, allowing the DNA strands to return to their double helical structure. This step is crucial as it ensures that the genetic information encoded in the DNA can be translated into a protein without interfering with the stable double-stranded structure of DNA. The peeling off of mRNA is essential for it to carry the genetic instructions from the nucleus to the ribosome, where translation into proteins occurs. The other choices do not accurately represent stage 3 of protein synthesis. The ribosome attaching to the DNA does not occur at this point since transcription has already taken place. Free amino acids binding to the ribosome is part of the translation process, which happens after the mRNA has detached. Lastly, the rejoining of DNA strands occurs after the mRNA has synthesized and released, not during the process of protein synthesis itself. Thus, the detachment of the mRNA is a key step in enabling the translation machinery to function correctly.