The genetic code – introns & exons

  • recall that in prokaryotic cells, DNA molecules are short, circular and not associated with proteins, while in the nucleus of eukaryotic cells, DNA molecules are very long, linear and associated with proteins, called histones
  • recall that the mitochondria and chloroplasts of eukaryotic cells also contain DNA which, like the DNA of prokaryotes, is short, circular and not associated with protein
    explain that a gene is a base sequence of DNA that codes for:

    • the amino acid sequence of a polypeptide
    • a functional RNA (including ribosomal RNA and tRNAs)
  • recall that a gene occupies a fixed position, called a locus, on a particular DNA molecule
  • recall that a sequence of three DNA bases, called a triplet, codes for a specific amino acid
  • recall that the genetic code is universal, non-overlapping and degenerate
  • define the terms ‘intron’ and ‘exon’