《分子生物学 Molecular Biology》课程教学课件（PPT讲稿，英文版）Chapter 17 The mechanism of translation I - initiation

Copyright The McGraw-Hill Companies,Inc.Permission required for reproduction or display. Chapter 17 The mechanism of translation I:initiation

Chapter 17 The mechanism of translation I: initiation

Initiation Translation了 Elongation Termination mRNA →Protein(peptide) Ribosome (factories) tRNA (adaptors)

Translation mRNA Protein (peptide) Ribosome (factories) tRNA (adaptors) Initiation Elongation Termination

Bacteria (recall operons)can dive into an initiation site in the middle of an mRNA; Eukaryotic ribosomes usually only need to find the single 5'initiation site

Bacteria (recall operons) can dive into an initiation site in the middle of an mRNA; Eukaryotic ribosomes usually only need to find the single 5’ initiation site

17.1 Initiation of prokaryotes -Before translation initiation -tRNA charging -Dissociation of ribosome -Formation of the 30s initiation complex -The first codon and the first aminoacyl tRNA -Binding mRNA to the 30s Ribosomeal subunit -Binding fMet-tRNAfMet to the 30s initiation complex -Formation of the 70s initiation complex

17.1 Initiation of prokaryotes -Before translation initiation -tRNA charging -Dissociation of ribosome -Formation of the 30S initiation complex -The first codon and the first aminoacyl tRNA -Binding mRNA to the 30S Ribosomeal subunit -Binding fMet-tRNAfMet to the 30S initiation complex -Formation of the 70S initiation complex

tRNA charging .All tRNAs have the same three bases (CCA)at their 3'- ends,and the terminal adenosine is target for charging. Figure 17.1 tRNA chain -O-P-C OH Ester bone H-C-R H3*

tRNA charging •All tRNAs have the same three bases (CCA) at their 3’- ends, and the terminal adenosine is target for charging. 3’ 2’ Ester bone

tRNA charging reaction 20 synthetases Figure 17.2 H O Aminoacyl-tRNA H,N-C-co0+⊙⊙⊙ synthetase HN-C-C-0- pp ⑧ OH OH OHOH () Amino acid ATP Aminoacyl-AMP H HN-0-® Aminoacyl-tRNA synthetase ⑧ OHOH OH OH OH OH Aminoacyl-AMP tRNA C=0 (2) (Terminal AMP adenosine) HN-C-一H ⑧ Aminoacyl-tRNA

tRNA charging reaction 20 synthetases

小结 √氨基酰-RNA合成酶连接氨基酸到它们 同源的tRNAs。 √这一过程通过两步特定的反应由ATP活 化氨基酸生成AA-RNA和AMP

小 结 ✓氨基酰-tRNA合成酶连接氨基酸到它们 同源的tRNAs。 ✓这一过程通过两步特定的反应由ATP活 化氨基酸生成AA-tRNA和AMP

Dissociation of ribosome .ribosome:contain 30s and 70s subunit .Two subunit have to dissociate after each round of translation for a new initiation complex. .The initiation factors that involve ribosome dissociation. ·IF-1 .IF-1 is actively promoting the dissociation. ·IF-3 .IF-3 binds to the free 30s subunits and prevents their reassociation with 50s subunits

Dissociation of ribosome •ribosome: contain 30S and 70S subunit •Two subunit have to dissociate after each round of translation for a new initiation complex. •The initiation factors that involve ribosome dissociation. •IF-1 •IF-1 is actively promoting the dissociation. •IF-3 •IF-3 binds to the free 30S subunits and prevents their reassociation with 50S subunits

Demonstration of ribosomal subunit exchange No exchange: Growth in light medium Heavy ribosome Heavy ribosome Light ribosome (labeled) (labeled) (unlabeled) Subunit exchange: Growth in light *50S medium *30S 火 Figure 17.3 Hybrid ribosomes Exchange (labeled) partners

Demonstration of ribosomal subunit exchange

10 Heavy:86S Light 0 hybrid ribosomal subunit can exchange 86S 70S (Heavy)Light) 01020304050607080 Figure 174

hybrid ➔ ribosomal subunit can exchange