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Lecture 32 Translation notes

Lecture 32 Translation notes - Lecture 32 Translation and...

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Lecture 32 Translation and Protein Targeting 6 th Ed. Chapter 17, pp. 313-321 KNOW figs 17.15, 17.17, 17.18, and 17.19 7 th Ed. Chapter 17, pp. 320-326. KNOW figs 17.16-17.19 Translation is protein synthesis, using the information in an mRNA molecule to specify the order of amino acids in a protein. One codon (3 nucleotides in a row) specifies 1 amino acid. Unlike DNA and RNA synthesis, we can’t use base pairing between a template and a new strand to make a protein. Instead, we need an adaptor: something that recognizes BOTH a specific amino acid AND a specific codon. Transfer RNAs (tRNAs) are these adaptors. tRNAs . tRNA molecules are about 80 nucleotides long. tRNAs are extensively folded, by internal base pairing. This means that short stretches of nucleotides in one part of the tRNA molecule are complementary to short stretches in another part of the same molecule. These stretches base pair with each other. The result is that tRNAs have secondary structure, and fold up into a compact, distinctive shape that would have a cloverleaf-like appearance if artificially flattened out. tRNAs interpret the genetic code by acting as adaptors. For this reason, there are many different tRNAs. Each tRNA has a sequence of 3 nucleotides called an anticodon at one end. Each anti-codon is designed to bind to a codon in an mRNA molecule, by base-pairing rules. At the other end, each tRNA binds to a specific amino acid. In a sense, tRNAs are the only molecules that actually "know" which codon corresponds to which amino acid. Before translation starts, amino acids are covalently linked to the correct tRNA molecule. To do this, an enzyme called an aminoacyl-tRNA synthetase binds a specific amino acid and a specific tRNA. There are many aminoacyl-tRNA synthetases; 1 for each tRNA and amino acid pair. Each enzyme SPECIFICALLY recognizes only the correct amino acid and the correct tRNA. This enzyme hydrolyzes ATP, and uses the energy to covalently link the tRNA and the amino acid. The result is an aminoacyl-tRNA; also called a charged tRNA . The Ribosome . To understand how translation works, we first need to know something about the structure of the ribosome. Ribosomes contain 2 subunits; the large subunit and the small subunit. Each contains 1 molecule of RNA and several polypeptides. The RNA in ribosomes is called rRNA. It is the most abundant RNA in the cell.
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