Where does transcription occur and what does it produce?

• A. Transcription copies DNA into mRNA in the nucleus; translation uses mRNA to assemble proteins at ribosomes in the cytoplasm.
• B. Transcription occurs in cytoplasm; translation occurs in nucleus.
• C. Both occur in mitochondria.
• D. Transcription copies RNA into DNA.

Answer: (A)

Transcription is the process of copying the information in a gene’s DNA into an RNA molecule. In a typical eukaryotic cell, this happens in the nucleus because DNA is housed there. The product is messenger RNA (mRNA), which carries the genetic message out of the nucleus to a ribosome. Translation then uses that mRNA as a template to assemble amino acids into a protein, a task carried out at ribosomes in the cytoplasm (often on the rough endoplasmic reticulum as well).

So transcription in the nucleus producing mRNA and then translation in the cytoplasm producing the protein is the standard flow of genetic information. Transcription in the cytoplasm would be unusual for most genes, copying RNA into DNA would be reverse transcription, and saying both processes occur in mitochondria ignores the common cellular arrangement in the rest of the cell.