tailieunhanh - Lecture Molecular biology: Chapter 17 - Robert F. Weaver

Chapter 17 - The mechanism of translation I: Initiation. This chapter concerns the initiation of translation in eukaryotes and bacteria. Because the nomenclatures of the two systems are different, it is easier to consider them separately. Therefore, let us begin with a discussion of the simpler system, initiation in bacteria. Then we will move on to the more complex eukaryotic scheme. | Molecular Biology Fourth Edition Chapter 17 The Mechanism of Translation I: Initiation Lecture PowerPoint to accompany Robert F. Weaver Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Initiation of Translation in Bacteria Two important events must occur before translation initiation can take place Generate a supply of aminoacyl-tRNAs Amino acids must be covalently bound to tRNAs Process of bonding tRNA to amino acid is called tRNA charging Dissociation of ribosomes into their two subunits The cell assembles the initiation complex on the small ribosomal subunit The two subunits must separate to make assembly possible 17- tRNA Charging All tRNAs have same 3 bases at 3’-end (CCA) Terminal adenosine is the target for charging with amino acid Amino acid attached by ester bond between Its carboxyl group 2’- or 3’-hydroxyl group of terminal adenosine of tRNA 17- Two-Step Charging Aminoacyl-tRNA synthetases join amino acids to their . | Molecular Biology Fourth Edition Chapter 17 The Mechanism of Translation I: Initiation Lecture PowerPoint to accompany Robert F. Weaver Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Initiation of Translation in Bacteria Two important events must occur before translation initiation can take place Generate a supply of aminoacyl-tRNAs Amino acids must be covalently bound to tRNAs Process of bonding tRNA to amino acid is called tRNA charging Dissociation of ribosomes into their two subunits The cell assembles the initiation complex on the small ribosomal subunit The two subunits must separate to make assembly possible 17- tRNA Charging All tRNAs have same 3 bases at 3’-end (CCA) Terminal adenosine is the target for charging with amino acid Amino acid attached by ester bond between Its carboxyl group 2’- or 3’-hydroxyl group of terminal adenosine of tRNA 17- Two-Step Charging Aminoacyl-tRNA synthetases join amino acids to their cognate tRNAs This is done in a two-step reaction: Begins with activation of the amino acid with AMP derived from ATP In the second step, the energy from the aminoacyl-AMP is used to transfer the amino acid to the tRNA 17- Aminoacyl-tRNA Synthetase Activity 17- Dissociation of Ribosomes E. coli ribosomes dissociate into subunits at the end of each round of translation IF1 actively promotes this dissociation IF3 binds to free 30S subunit and prevents reassociation with 50S subunit to form a whole ribosome 17- Ribosomal Subunit Exchange 17- Formation of the 30S Initiation Complex When ribosomes have been dissociated into 50S and 30S subunits, cell builds a complex on the 30S subunit: mRNA Aminoacyl-tRNA Initiation factors IF3 binds by itself to 30S subunit IF1 and IF2 stabilize this binding IF2 can bind alone, but is stabilized with help of IF1 and IF3 IF1 does not bind alone 17- First Codon and the First Aminoacyl-tRNA Prokaryotic initiation codon is: Usually AUG Can .