Cellular Control

Cellular Control

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Gene - length of DNA, codes for one or more polypeptides.

Sequence of nucleotide bases on a gene provides a code. It is a triplet code (3 nucleotide bases).


  • First stage of protein synthesis. One strand of DNA is used as a template.
  • Gene unwinds and unzips. H bonds between complimentary bases break.
  • RNA nucleotides bind to exposed bases.
  • mRNA is complementary to template DNA strand.
  • mRNA is released from the DNA and passes out of the nucleus through a pore in the nuclear envelope.
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Second stge of Protein Synthesis. Amino acids are arranged in a sequence dictated by the sequence of codons on mRNA.

Sequence of Amino acids is important because :

  • Forms Primary structure of a protein.
  • Primary structure determines tertiary structure.
  • Tertiary structure allows protein to function, if altered the active site may have altered shape.
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Translatin continued.

How the Polypeptide is assembled.

  • Molecule of mRNA binds to a ribosome. 2 codons attached to small sub unit of the ribosome and exposed to large unit of ribosome.
  • Second tRNA, with different amino acid binds to second exposed codon.
  • Peptide bond forms between two adactent amino acids.
  • Ribosome moves along the mRNA reading the next codon. Third tRNA brings another amino acid and a peptide bond forms between it and the dipeptide. First tRNA leaves and can collect and bring another amino acid.
  • Polypeptide chain grows until a stop codon is reached.
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