5 Where does transcription occur in the cell?
Up to now we have described the processes of transcription without considering where each occurs within the cell.
Given that transcription — the production of mRNA — requires a DNA template, where do you think this process occurs in the cell?
It must occur in the nucleus where the DNA in the cell is located.
However, once mRNA is produced, it leaves the nucleus and protein synthesis – translation – occurs in the cytoplasm. Thus transcription and translation are separated both in space within the cell and in time, in that one occurs after the other, as shown schematically in Figure 11.8. Thus the role of mRNA is to carry a coded message from the nucleus where the information is stored, to the cytoplasm where the coded message is translated into a specific protein; hence it’s name – messenger RNA.
Translation occurs at particular sites within the cytoplasm; it occurs on ribosomes. Ribosomes are large aggregates of proteins and ribosomal RNA (rRNA). Hence three types of RNA are involved in the process of translation but only one of them, mRNA, codes for proteins.
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