When does protein expression occur?

The primary control point for protein expression is during the initiation of transcription. RNA transcription is an efficient control point because many proteins can be generated from a single mRNA molecule. Genetic information in the DNA is decoded through transcriptional processes to produce mRNA. The information coded by mRNA is then translated into a protein. In prokaryotic cells, the process of transcription and translation occurs simultaneously. In eukaryotes, the process of transcription and translation is separate. Transcription occurs in the nucleus, and translation occurs in the cytoplasm. In translation, ribosomes decode the mRNA sequence in sets of three nucleotides (codons). tRNA molecules each carry a specific amino acid, and recognize the codons on the mRNA through their complementary anticodons. The ribosome then catalyzes the formation of peptide bonds between amino acids, resulting in the synthesis of a polypeptide chain.