生物化學(xué)Proteinsynthesis課件

1、ProteinsynthesisChapter 13Reverse transcriptiontranslation The nucleotide sequence of mRNA is translated into a sequence of amino acids by a genetic code(遺傳密碼) from its 5 end to 3 end.what the translation needs mRNA (template) amino acids (materials) ribosome (factory, rRNA and protein) ATP and GTP

2、(energy) tRNA (carrier, interpreter)遺傳密碼mRNA 分子中所儲(chǔ)存的遺傳信息是由其分子的四種堿基以特定順序排列成的三個(gè)一組的三聯(lián)體代表的，每種氨基酸都有其特定的三聯(lián)體密碼。That means three nucleotides produce one amino acid(43).the genetic code is degenerate(簡(jiǎn)并). in most cases, one amino acid is coded by several codons, which are called synonymous codons(同義密碼子). the

3、 genetic code is wobbling(擺動(dòng)) each codon is recognized by a triplet of bases, called an anticodon(反義密碼子) in RNA. Each codon base pairs with its complementary anticodon base. However, the pairing of the third base of a codon is less stringent than for the first two bases. 13.2 Transfer RNA the second

4、ary structure of tRNA is cloverleaf(三葉草形). It contains five arms: acceptor stem(受體臂), D arm(雙氫尿嘧啶臂), TC arm(假尿嘧啶臂), anticodon arm and extra arm. the tertiary structure of tRNA is an inverse “L” form.The function of tRNA Each tRNA becomes covalently bonded to a specific amino acid to form aminoacyl-t

5、RNA (氨酰tRNA) which recognizes the corresponding codon in mRNA and ensures that the correct amino acid is added to the growing polypeptide chain.13.4 Process of translation During translation the mRNA is read from 5 end to 3 end, and protein is synthesized in an N terminal to C terminal direction.Pri

6、nciple for DNA replication: base-pairingPrinciple for protein synthesis: anticodon-codon base-pairing （反密碼子密碼子） Amino acid + tRNA + ATP Aminoacyl-tRNA +AMP + PPiaminoacyl-tRNA synthetase(氨酰tRNA合成酶)Each tRNA carries only a single amino acid, and a separate aminoacyl-tRNA synthetase exists for every a

7、mino acid. In prokaryotes the initial amino acid is fMet (甲酰甲硫氨酸)，and the corresponding initial aminocyl-tRNA is fMet-tRNAfMet； In eukaryotes, the initial amino acid is Met，the corresponding initial aminoacyl-tRNA is Met-tRNAMet.Initiation stepP位A位The small subunit (30S) binds to the mRNAThe initiat

8、or tRNA charged with N-formylmethionine (fMet-tRNA) binds to form the 30S initiation complex (30S起始復(fù)合物)The large ribosomal subunit binds to form a 70s initiation complex (70S起始復(fù)合物) with the hydrolysis of GTPElongation of peptide chainAminoacyl-tRNA binding : the corresponding aminacyl-tRNA for the s

9、econd codon binds to the A site（進(jìn)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 (轉(zhuǎn)肽酶)Translocation (移

10、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)After translocation, the A site is empty and ready to receive the next aminoacyl-tRNA.Energy yieldAmino acid activation: 2 ATPFormation of 70S initiation complex :1 GTPAminoacyl-tRNA binding t