Protein Synthesis - Translation
Translation = the assembly of polypeptides at the ribosomes.The polypeptides are assembeld into the sequence dictated by the sequence of codons on the mRNA
The genetic code is translated into a sequence of amino acids = make up the polpeptide
Anticodon = a sequence of three adjacent nucleotides in transfer RNA, which designates a specific amino acid.
1) The mRNA molcule binds to a ribosome (either in the cytoplasm or on the RER)
2) Two codons (six bases, three bases for each codon) attach to the small subunit of the ribosome. They are exposed to the large subunit of the ribosome.
3) The first codon is ALWAYS AUG so the anticodon UAC binds to the codon by hydrogen bonds. A transfer RNA (tRNA) brings the anticodon to the codon, using ATP and an enzyme.
4) A tRNA molecule brings a different amino acid to the second exposed codon. The amino acid has a complementary anticodon.
5) A peptide bond forms between the two adjacent amino acids. An enzyme within the small subunit of the ribosome cataylses the reaction.
6) The ribosome moves along the mRNA molecule. Another amino acid is brought to the strand by tRNA. Hydrogen bonds form between the codon and the amino acid and a peptide bond forms between the amino acid and the dipeptide.
7) The polypeptide chain grows until a "stop" codon is reached, UAA, UAC or UGA. There are no corresponding tRNA's for these codons.