1/18/2016 64 codons but only 20 amino acids The Genetic Code AT G Degeneracy-most O A amino acids use more Second leeer than one codon Degeneracy allows for A U O a certain amount of mutation without affecting the protein 61 sense codons that code for amino acids 3 non-sense codons that do not but rather signal the end of protein synthesis Translation Initiation Translation Elongation Ribosomes direct the binding of tRNAs to the codons and ·A second tRNA with the assemble the amino acids into a complementary anticodon chain producing a protein. fills the A site (aminoacyl). Ribosomes assemble on the 5'end A peptide bond is formed of a mRNA transcript. and the polypeptide is mRNA until it attached to the tRNA in t codon,usually the P site. AUG,which codes for methionine. The ribosome moves along .A tRNA molecule with the the mRNA u anticodon and the second peiteerT0afqemtwwne tRNA is in the P site. ne am no ac id enters the The first tRNA is now in and binds to the mRNA. the E site. A second tRNA carrying the Another tRNA fills the A second amino acid approaches site. 1/18/2016 10 The Genetic Code • 64 codons but only 20 amino acids • Degeneracy – most amino acids use more than one codon • Degeneracy allows for a certain amount of mutation without affecting the protein • 61 sense codons that code for amino acids • 3 non-sense codons that do not but rather signal the end of protein synthesis • Ribosomes direct the binding of tRNAs to the codons and assemble the amino acids into a chain producing a protein. Translation Initiation • Ribosomes assemble on the 5′ end of a mRNA transcript. • Ribosome scans the mRNA until it reaches the start codon, usually AUG, which codes for methionine. • A tRNA molecule with the complementary anticodon and methionine amino acid enters the P site (peptidyl) of the ribosome and binds to the mRNA. • A second tRNA carrying the second amino acid approaches. • A second tRNA with the complementary anticodon fills the A site (aminoacyl). id b d i f d Translation Elongation • A peptide bond is formed and the polypeptide is attached to the tRNA in the P site. • The ribosome moves along the mRNA until the second tRNA is in the P site. • The first tRNA is now in the E site. • Another tRNA fills the A site