DNA structure

• • DNA is polymer made from four different nucleotides
  • each nucleotide is made up of sugar, phospate group and base
  • sugar and phospate group form backbone to DNA
  • sugar and phospate groups alternate
• • there are four bases - A, T, C, G
  • complementary base pairing:
  • A links with T
  • C links with G
  • order of bases in gene decides order of amino acis
  • each animo acid coded for by three bases
• • parts of DNA do not code for proteins
  • non-coding parts of DNA switch genes on and off
  • so, control whether gene is expressed - used to make protein
• • proteins made in cytoplasm on ribosomes
  • ribosomes need code in DNA to make proetins
  • DNA is in nucleus
  • so, code from DNA needs to be transported to ribosome
  • mRNA copies code from DNA and carries code to ribosome
  • messenger between DNA and ribosomes
  • correct amino acids brought to ribosomes in correct order by carrier molecules
• • when a protein chain is complete, it folds up to form unique shape
  • shape enables protein to do job as:
  • enzymes - biological catalysts to speed up chemical reaction in body
  • hormones - carry messages around body
  • structural proteins - physically strong e.g collagen that strengthens ligaments