生物化学ProteinsynthesisPPT课件.ppt

Chapter 13 Proteinsynthesis what the translation needs 13.1 The genetic code 遗传密码 mRNA 分子中所储存的遗传信息是由其分子的四种碱基以特定顺序排列成的三个一组的三联体代表的，每种氨基酸都有其特定的三联体密码。 13.2 Transfer RNA 13.3 Ribosomes 13.4 Process of translation Principle for DNA replication: base-pairing Principle for protein synthesis: anticodon-codon base-pairing （反密码子－密码子） Initiation step The small subunit (30S) binds to the mRNA The initiator tRNA charged with N-formylmethionine (fMet-tRNA) binds to form the 30S initiation complex (30S起始复合物) The large ribosomal subunit binds to form a 70s initiation complex (70S起始复合物) with the hydrolysis of GTP Elongation of peptide chain Aminoacyl-tRNA binding : the corresponding aminacyl-tRNA for the second codon binds to the A site（进位）（GTP hydrolysis） Peptide bond formation: the carboxyl end of the amino acid bound to the tRNA in the P site becomes joined by a peptide bond to the amino group of the amino acid linked to the tRNA in the A site，catalyzed by peptidyl transferase (转肽酶) Translocation (移位): ribosome moves along the mRNA (5’ to 3’) by three nucleotides so that the dipeptidyl-tRNA in the A site moves to the P site to place the next codon in the A site (GTP hydrolysis) Termination (合成终止) Termination codons appear at the A site (UAG,UAA, UGA) Release factors (终止因子) binds to the ribosome. Peptidyl transferase is transformed to become a hydrolase(水解酶) so that the polypeptide is transferred to a water molecule, effectively cleaving the bond between the polypeptide and tRNA in the P site. Then the polypeptide leaves the ribosome, flollowed by mRNA and free tRNA. The ribosome dissociates into 30S and 50S subunits ready to start translation afresh. (1 ATP) Energy yield Amino acid activation: 2 ATP Formation of 70S initiation complex :1 GTP Aminoacyl-tRNA binding to A site: 1 GTP Translocation: 1 GTP Polyribosome * * Reverse transcription translation The nucleotide sequence of mRNA is translated into a sequence of amino a