CELLULAR CONTROL

Cellular control module (1) for F215 OCR Biology

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TRANSCRIPTION

Key definition - the creation of a single-stranded mRNA copy of the DNA coding strand

1st stage of protein synthesis:

  • Hydrogen bonds between complementary bases in the DNA molecule break
  • RNA polymerase allows free RNA nucleotides to bind to their exposed complementary bases on the template strand of DNA by hydrogen bonding
  • The mRNA is released from the DNA and passes out of the nucleus, through a pore in the nuclear envelope, to a ribosome
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TRANSLATION

Key definition - the assembly of polypeptides (proteins) at ribosomes

2nd stage of protein synthesis:

  • The mRNA molecule binds to a ribosome - the first exposed mRNA codon is always AUG, which means a tRNA with methionine and the anticodon UAC hydrogen bonds with this initial codon
  • A second tRNA, bearing a different amino acid, binds to the second exposed codon with its complementary anticodon
  • A peptide bond forms between the two adjacent amino acids
  • The ribosome moves along the mRNA to read the next codon so a tRNA brings another amino acid so a peptide bond forms between it and the dipeptide
  • The first tRNA leaves to collect and bring another of its amino acids
  • The polypeptide chain grows until a stop codon is reached and then the polypeptide chain is complete
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