Module 5

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Module 5
2012-12-10 21:13:01
Biomedical core

Objective 10
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  1. A sequence of mRNA bases that codes for a protein is called a
  2. The complementary sequence of tRNA bases is called
    an anticodon
  3. The acceptor arm "stem" carries
    an amino acid
  4. Each tRNA type has a specific anticodon at one end and a "matching"
    amino acid at the other.
  5. What shape is tRNA?
    Cloverleaf-shaped RNA molecule
  6. Step 1 of 7 in the translation process:
    Ribosomes attaches to mRNA: Ribosome assembly. 5'-AUG-3' is always the start codon. Its anticodn is 5'-CAU-3' (remember, it's antiparallel and complementary). The tRNA with the anticodon CAU always carries a methionine. When the AUG start signal is detected on the mRNA, Met-tRNA binds there.
  7. Step 2 of 7 in the translation process:
    AUG start codon matches up to tRNA-methionine: The binding of Met-tRNA triggers self-assembly of the ribosome at the site of tRNA binding. The large (60S) ribosomal subunit always assembles fo that the Met-tRNA is enveloped in the P site. The A site is empty at this point.
  8. Step 3 of 7 in the translation process:
    tRNA-amino acid arrives: Ribosome is assembled and ready to begin synthesis of the protein strand.  The next codon is read.  The Asp-tRNA nestles into the A site, next to the Met-tRNA which is still in the P site.
  9. Step 4 of 7 in the translation process:
    Peptide bonds form: Amino acids who find themselves snuggled together in the P and A sites decide they might as well form a peptide bond.  When they do, the synthesis of protein has begun. The methionine is transferred to the Asp-tRNA and the tRNA which used to carry methionine is released to go get another one. This leaves the P site open.
  10. Step 5 of 7 in the translation process:
    Ribosome shifts three mRNA bases (met-tRNA is released, open spot occupied by new amino acid-tRNA): Met-Cys-tRNA moves inot the vacant P site as the ribosome ratchets three bases down (i.e., toward the 3' end) the mRNA molecule. Now, the A site is empy. The next codon is 5'-AUU-3'. This codes for isoleucine, so the Ile-tRNA will be bound to the ribosome complex at that site.
  11. Step 6 of 7 in the translation process:
    Polypeptide chain grows: Process continues, and the polypeptide chain grows.
  12. Step 7 of 7 in the translation process:
    Ribosome reaches stop codon; polypeptide released: The stop codon is reached. There is no tRNA for the stop codon; rather, the stop codon leaves the A site empy and the full-length protein is bound to the last tRNA at the P site. The ribosome disassembles, and the tRNA, protein, and ribosomal subunits all drift wawy from each other.