Translation is the process by which polypeptide chains are built, subsequently forming proteins destined to perform a variety of functions in the body. It involves 3 main steps: initiation, elongation, and termination. The mRNA strand formed in transcription attaches to a free ribosome in the cell cytoplasm. The first step of translation then begins. (1) Initiation is the recognition of a start codon, often AUG, on the mRNA strand, and begins the formation of the polypeptide chain. A tRNA molecule bound to the A site (think 'arrival') of the small ribosome sub-unit grabs a methionine amino acid and attaches it to the codon to begin translation at the P site of the small ribosome unit. (2) Elongation is the second step of translation where the polypeptide chain grows (elongates!) at the P site of the small ribosome sub-unit. Each codon (three letter code on the mRNA strand) is matched to a specific amino acid that will be attached to the growing polypeptide chain. After the tRNA molecule has contributed its amino acid to the chain, it occupies and leaves at the E site (think 'exit'). (3) Termination is the third and final step of translation, which is marked by the recognition of a stop codon, which can be UUA, UGA, or UAG, and ends the translation of the mRNA strand. The resulting polypeptide chain (also known as a primary structure of a protein) goes on to take on a specific shape, which depends on the chemical properties of its amino acids. The resulting molecule will be a protein (put simply!).
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