Chapter30Notes 11.45.23 PM

Chapter30Notes 11.45.23 PM - Page 1 of 20 Figures/Notes for...

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Page 1 of 20 KEY CONCEPTS : ! Translation : the process whereby the genetic code represented in a mRNA is translated into an amino acid sequence of a polypeptide. ! Once again, E. coli is the best understood system and will be discussed in detail, but some features of eucaryotic protein synthesis will be discussed. ! Translation involves over 100 different macromolecules, making it much more complex than those for replication and transcription. ! Amino-acyl tRNAs (aa-tRNAs) are activated amino acid donors for protein synthesis. The amino acid is covalently linked by its C00H group to the 3'( or 2')-OH terminus of its cognate tRNA. ! aa-tRNAs are synthesized by aa-tRNA synthetases (at least one kind per amino acid) in reactions which require the energy form ATP hydrolysis. ! Errors occur in the process about once in 1-10,000 a.a.’s incorporated into proteins. Several “proofreading” mechanisms contribute to assure this accuracy. ! Base-pairing matches mRNA code words (codons) with recognition sequences (anticodons) for each amino acid. ! Protein synthesis occurs in the amino to carboxy terminal direction. Amino acids are added to the C00H end of the growing polypeptide chain. mRNA codons are read from 5' 6 3' direction. ! The ribosome is a ribozyme involved in catalysis of peptide bond formation. Figures/Notes for Chapter 30 Biochemistry 461 Fall 20 10 CHAPTER 30: PROTEIN SYNTHESIS LECTURE TOPICS ! TRANSLATION (mRNA 6 protein) COMPLEXITY, STAGES ! tRNAs and AMINO ACID ACTIVATION ! tRNA: re GENETIC CODE AND TRANSLATION ! RIBOSOME STRUCTURE ! TRANSLATION PROCESS ! PROCARYOTIC, EUCARYOTIC, INHIBITORS
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Page 2 of 20 THERE ARE THREE DISTINCT STAGES OF PROTEIN SYNTHESIS. ! Initiation - Initiator tRNA binds to a start signal on mRNA and base-pairs with the AUG codon. The complex occupies the ribosome P (peptidyl) site. Base-pairing of mRNA sequences near the start signal with 16S RNA in the small ribosome subunit is also required. Requires GTP hydrolysis for energy. ! Elongation begins when an aa-tRNA binds to the ribosome A (amino acyl) site. Then a peptide bond is formed between the COOH group of the amino acid of the aa-tRNA in the P site with the NH 2 group of the amino acid on an aa-tRNA in the A site. The resultant dipeptidyl-tRNA is moved (translocated) from the A to the P site, displacing the tRNA from the P-site to the E site (exit site). The process repeats (powered by GTP hydrolysis) until the stop codon is reached. 23S rRNA is a “ribozyme” finvolved in catalysis of peptide bond formation. ! Termination occurs when specific protein release factors for each stop codon cause hydrolysis of the nascent polypeptide chain from the peptidyl tRNA and its release from the ribosome. !
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Chapter30Notes 11.45.23 PM - Page 1 of 20 Figures/Notes for...

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