Translation occurs in living cells. Explain how translation is carried out, from the initiation stage onwards.

Translation is the process where mRNA in the cytoplasm becomes a functional protein. Translation follows transcription, where an mRNA for a protein-coding gene is made. The mRNA leaves the nucleus through pores and is translated in the cytoplasm. Amino acids, the building blocks of proteins, are activated for transcription by specialised tRNA molecules (transfer RNA). The formation of a tRNA/amino acid complex is catalysed by a tRNA-activating enzyme and requires ATP. There is a specific tRNA for all 20 amino acids. Each tRNA has a different anticodon, which is complementary to a codon of mRNA. A codon is a 3 base pair sequence. Translation is carried out by a ribosome consisting of a large and small subunit, and has a catalytic function. The ribosome has an A, P, and E site where the amino acid carrying tRNAs can interact. There are three stages: initiation, elongation, and termination. Translation is carried out as follows:Initiation: an mRNA molecule binds to the small ribosomal subunit and slides in a 5' to 3' direction until start codon 'AUG' is reached on the mRNA. An initiator tRNA carrying methionine binds to the start codon 'AUG' at the P site on the ribosome. The large ribosomal subunit binds to the small subunit and a second tRNA with an amino acid binds to complementary mRNA at the A site. A peptide bond forms between methionine and the other amino acid. Inactivated tRNAs leave ribosome at E site. Elongation: mRNA continues to slide along the ribosome in a 5' to 3' direction. Complementary tRNAs carrying amino acids come in and move from the A site to the P site and are inactivated when their amino acid forms a peptide bond with adjacent amino acids. Then the inactivated tRNAs leave at the E site. An elongating strand of amino acids is formed by the ribosome. Termination: translation ends when a stop codon is reached, 'UAA' 'UAG' or 'UGA'. The polypeptide is released and the two ribosomal subunits disassemble.