PPP_Ch 15 - CHAPTER 15 Translation and proteins Dr....

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CHAPTER 15 Translation and proteins Dr. Sanghamitra Mohanty
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15.1 Translation of mRNA Depends on Ribosomes and Transfer RNAs Translation is the biological polymerization of amino acids into polypeptide chains. This process requires: amino acids messenger RNA (mRNA) ribosomes transfer RNA (tRNA)
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Ribosomes consist of ribosomal proteins and ribosomal RNAs (rRNAs). They have a large subunit and a small subunit ( Figure 15.1 ). The rRNAs provide for important catalytic functions associated with translation . .
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They are 75–90 nucleotides long and contain posttranscriptionally modified bases. The two-dimensional structure of tRNAs is a cloverleaf ( Figure 15.3 and Figure 15.4 ). tRNAs serve as adaptor molecules to adapt the triplet codons in mRNA to the correct amino acid.
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A tRNA has an anticodon that base-pairs with the codon in the mRNA. The corresponding amino acid is bound to the CCA sequence at the 3' end of all tRNAs.
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Aminoacyl tRNA synthetase charges (activates) tRNAs with the appropriate amino acid.
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15.2 TRANSLATION OF MRNA  CAN BE DIVIDED INTO  THREE STEPS Initiation Elongation Termination
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Initiation requires: the small and large ribosomal subunits GTP charged initiator tRNA initiation factors; IF I, II and III ( Figure 15.6 )
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In bacteria, the AUG start codon is preceded by a Shine-Dalgarno sequence , which base-pairs with a region of the 16S rRNA of the 30S small subunit. Elongation requires both ribosomal subunits assembled with the mRNA to form the P (peptidyl) site and A (aminoacyl) site ( Figure 15.7 ).
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The charged tRNAs enter the A site, and The charged tRNAs enter the A site, and peptidyl peptidyl transferase transferase catalyzes peptide bond formation
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PPP_Ch 15 - CHAPTER 15 Translation and proteins Dr....

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