Translation_geneexpinbrief_nucleus_structure_and_epigenetics

Translation_geneexpinbrief_nucleus_structure_and_epigenetics

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Genetic Code mRNA code to amino acid code
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Starting Translation
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Degeneracy (redundancy) of the code UAU Tyr UGU Cys UAC Tyr UGC Cys UAA Stop UGA Stop UAG Stop UGG Trp In this small corner of the universal decoder chart you see that several codons can encode the amino acids or stop signals. Given amino acids tend to be encoded by related codons (UAU or UAC, for example). This helps reduce the likelihood that base substitutions change the amino acid sequence of a protein.
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Base pairing can be sloppy (wobble) at the 3’ position of the codon U of tRNA can pair with A or G of mRNA G of tRNA can pair with U or C of mRNA I (inosine, derivative of guanine) can pair with U, C, or A
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tRNA provides link between aa’s and codons 1 anti-codon can recognize > 1 mRNA codon For replication and transcription, the cell uses base pairing of complementary nucleotides… what about translation? The problem: the structures of amino acids and nucleotides are not complementary. The solution: tRNA serves as an intermediary. one end - attached to a specific amino acid other end - complementary to codon (“anticodon”)
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transfer RNA (tRNA) Made by RNA polymerase III in eukaryotes 70-90 nucleotides long Contains 1. a conserved region (3’-ACC) where the amino acid is attached and 2. a unique region called the “anticodon triplet” 3. The red and blue are the D and T arms, which help with recognition by the ribosome Amino acid binding site
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Getting the tRNA ready for translation AA’s are added onto the free 3’ OH of tRNA This process is called “charging” -O-P-O-C-C-NH 2 O O O = = R - H
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Cellular machine for protein synthesis: ribosome Shown are the prokaryotic ribosome subunits Composition: two subunits: small & large 60% rRNA (initiation, alignment, peptide bond) 40% proteins 4.2 x 10 6 Da over 100,000 atoms X-ray structure (a big deal) See http://www.rcsb.org/pdb/molecules/pdb10_1.html 30S subunit 50S subunit
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The 30S (small) and 50S (large) subunits come together to form three functional tRNA binding sites in bacteria: similar in eukaryotes The active sites on the ribosome for tRNA are mostly RNA
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Simplified view of the ribosome E
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Translation Nobelprize.org Protein Synthesis Animation Video http://www.youtube.com/watch?v=Ikq9AcBcohA&feature=related
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Summary of initiation in prokaryotes or eukaryotes tRNA-Met binds IF2-GTP and small subunit tRNA-Met enters P site Small ribosome subunit binds to mRNA Initiation factors (IFs) helps assemble the small ribosome subunit-mRNA complex.
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