Regulation of gene expression after transcription
The regulation of gene expression can still occur after mRNA has left the nucleus, and once a polypeptide has been synthesised.
The product of a gene usually needs modification before it is functional.
Post-transcriptional modification: The transcribed mRNA sequence can be altered to influence the rate of translation and to alter the function of the protein produced.
Sections of mRNA can be removed to change the proteins that will be produced.
Post-transcriptional modification is a more common form of gene regulation in eukaryotes than in prokaryotes.
Translation: Proteins and some RNA molecules can bind to specific mRNA sequences during translation. This stops translation by preventing tRNA and ribosomes from binding to the mRNA.
Post-translational modification: once a polypeptide has been transcribed, the protein can be altered or activated by changing its structure.
Similarly, the rate of protein degradation can be controlled. This enables the cell to respond to changes in its environment, and to only use the most functional new proteins.