Transcription and translation

• Describe the stages in transcription of a gene?


  DNA helicase breaks the hydrogen bonds separating the helix.

  Complementary RNA nucleotides form hydrogen bonds with the bases of exposed nucleotides.

  RNA polymerase joins the RNA nucleotides together forming phosphodiester bonds.

  The enzymes make their way along DNA until end gene.

  mRNA formed - complementary to antisense strand

  Thymine is replaced by uracil.

  RNA polymerase detaches from DNA and helix reforms.

  mRNA exits the nucleus
• Describe the stages of translation

  mRNA binds to start codon on small subunit on ribosome.

  tRNA with complementary anticodon and amino acid, binds to mRNA start codon.

  Another tRNA moves into place, the anticodon on this tRNA is complementary to second codon on mRNA.

  The amino acids bind together by a peptide bond - catalysed by peptidyl transferase.

  The ribosome moves along, the tRNA then detaches and leaving behind the amino acid.

  Forms polypeptide.

  stop codon then releases the polypeptide.