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24 Cards in this Set
- Front
- Back
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What does the AUG codon do?
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Acts as the initiation codon and specifies methionine
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What are the stop codons?
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UAA, UAG, UGA
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What is the purpose of tRNA?
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Intermediates between mRNA and amino acids
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How long are tRNAs?
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~80 nucleotides
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What is the anticodon?
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Unpaired nucleotide triplet sequence that recognizes the codon on mRNA
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What are aminoacyl-tRNA synthases?
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Enzymes that couple each amino acid to its appropriate tRNA molecule
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How does aminoacyl-tRNA synthase work?
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It is a two step ATP-dependent rxn
1. Amino acid is activated by linking to AMP 2. AA is joined by an ester linkage to the 3'-OH of the tRNA molecule |
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What is the functional reaction of protein synthesis?
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Formation of peptide bond between carboxyl group of growing chain and free amino group of incoming AA
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What direction is protein synthesized?
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Amino (N)-terminal end to its carboxyl (C)-terminal end
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What is the composition of the ribosome?
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Composed of > 50 proteins and several RNA molecules, composed of 2 subunits 60S and 40S which together constitute an 80S particle; subunits are separate when not synthesizing protein
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How frequently is there a mistake in protein synthesis?
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1 in 10,000 AAs
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How many binding sites does the ribosome contain?
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4
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What is the E site?
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Exit site
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What is the P site?
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Peptidyl-tRNA
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What is the A site
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Aminoacyl-tRNA
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Why are the A and P sites close together?
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To insure formation of bp bonding of tRNAs with codons on mRNA, keeping correct reading frame
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What is the first step of protein elongation?
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Aminoacyl tRNA binds to ribosomal A site by base pairing w/codon on mRNA and a used tRNA is ejected from the E site
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What is the second step of protein elongation?
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New peptide bond is formed, carboxyl end of polypeptide chain is release from tRNA at the P site
-Breakage of bond between peptide tRNA and its AA |
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What is the third step of protein elongation?
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Large subunit translocates, relative to mRNA shifting the 2 tRNAs into the P and E sites
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What is the 4th step of protein elongation?
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Series of conformational changes advance the small subunit and the bound mRNA exactly 3 nucleotides through the ribosome and resetting the ribosome to be ready to receive next incoming amino-acyl tRNA
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What factors ensure the accuracy and efficiency of translation in eukaryotes?
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EF1 and EF2
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What factors ensure the accuracy and efficiency of translation in bacteria?
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EF-Tu and EF-G
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How do elongation factors work?
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Enter and leave the ribosome during each cycle, hydrolyzing GTP to GDP
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Can protein synthesis occur in vitro on ribosomes without the factors?
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Yes, but it is slow, inaccurate and inefficient
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