The part of protein synthesis that involves decoding the sequence of triplets in messenger RNA, and the concurrent formation of a polypeptide based on that sequence. Translation occurs on ribosomes in the cytoplasm, the proteins being synthesized from the amino terminal. The process is highly endergonic requiring four ATP equivalents per amino acid residue. Four stages may be recognized: activation, initiation, elongation, and termination. During activation amino acids are attached to small soluble * transfer RNA (tRNA) molecules in the cytosol. Each tRNA is specific for one amino acid. In initiation * messenger RNA (mRNA), transcribed from nuclear DNA, attaches to the ribosome. An initiating codon on the mRNA codes for a particular ami-noacyl tRNA, which binds to the mRNA at the ribosome. During elongation another aminoacyl tRNA now binds to the ribosome next to the first, and the two amino acids react to form a dipeptide on the second tRNA. The ribosome then moves along the mRNA, releasing the first tRNA molecule. A third aminoacyl tRNA now attaches to the ribosome and the process repeats, continuing until the full polypeptide chain is formed. At termination, a termination codon on the mRNA causes the release of the completed protein from the final tRNA molecule. The last tRNA and the mRNA then dissociate from the ribosome. Compare transcription. |
