Stages of protein synthesis. Illustration of the synthesis of proteins in cells using the instructions in messenger ribonucleic acid (mRNA). The mRNA strand (green) is read by temporarily formed ribosomes (small subunit, yellow; large subunit, orange). These move from the 5' to the 3' end of mRNA. Protein synthesis occurs between the start (AUG) and stop codons (dark green). The protein chain (polypeptide, blue) grows from N-terminal initiation (top left) through elongation (centre) to C-terminal capping or termination (lower right). The ribosome subunits are then released until needed again. For this artwork with labels, see C023/8872.