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

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Why is mRNA necessary for protein synthesis?

It prevents protein degradation
DNA cannot leave the nucleus
mRNA enhances ribosome function
mRNA regulates gene expression

The correct answer is: DNA cannot leave the nucleus

mRNA, or messenger RNA, plays a crucial role in protein synthesis because it serves as the bridge between DNA in the nucleus and the ribosomes in the cytoplasm, where proteins are produced. DNA contains the genetic blueprint for all the proteins a cell can make, but it is located in the nucleus and cannot leave this compartment. This spatial separation requires a messenger, which is the mRNA. During transcription, a specific segment of DNA is transcribed into mRNA, which then exits the nucleus through nuclear pores. Once in the cytoplasm, mRNA guides the ribosomes in assembling amino acids into a polypeptide chain, following the sequence of codons that corresponds to the original DNA template. This process ensures that the genetic information encoded in DNA is accurately translated into functional proteins necessary for various cellular processes. Other options, while they might have relevance in a broader biological context, do not directly explain the essential function of mRNA in the process of protein synthesis as clearly as the role of mRNA in conveying information from DNA to the ribosomes.