LEC11 - C B A Interaction between tRNA and mRNA There are...

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C B A
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Interaction between tRNA and mRNA There are 61 codons (3 stop codons). Cells contain only 30 - 40 tRNAs. Therefore, a single tRNA needs to be able to recognize more than one codon. This is possible because unusual pairings are allowed at the third position of the codon (wobble position)
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Due to the 3D structure of the tRNA, imperfect pairing is acceptable
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Wobble pairing allows a single tRNA to read more than one codon
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Examples of unusual base pairs found between codons and anticodons in the 3rd position Deaminated adenosine
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61 codons (3 stop codons) ~40 tRNAs 20 amino acids More than one anticodon (tRNA) per amino acid Many tRNAs can recognize more than one codon (wobble)
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Example: Alanine GCU GCC GCA GCG Codons (degeneracy) 5’ 3’ tRNA anticodon IGC IGC IGC CGC (Wobble) 5’ 3’
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What codons will be recognized by a tRNA with an anticodon 5’ IUA 3’ A. 5’ AAU 3’, 5’ UAU 3’, 5’ CAU 3’ B. 5’ UAA 3’, 5’ UAU 3’, 5’ UAC 3’ C. 5’ AAU 3’, 5’ UAU 3’, 5’ CAU 3’, 5’ AGU 3’, 5’ UGU 3’, 5’ CGU 3’ D. 5’ UAA 3’, 5’ UAU 3’, 5’ UAC 3’, 5’ UGA 3’, 5’ UGU 3’, 5’ UGC 3’
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Charging of tRNA Catalyzed by tRNA synthetases Two-step reaction requiring ATP (example of adenylylation) One tRNA synthetase for each amino acid
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Recognition of tRNA by aminoacyl-tRNA synthetase Anticodon Discriminator site: 4 th base from 3’ end D-loop
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Models of the complexes between tRNA and aminoacyl-tRNA synthetase blue = synthetase red = tRNA yellow = ATP
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