The Genetic Code

• Gene


  A sequence of nucleotides that forms part of a DNA molecule (one DNA molecule contains many genes)
• Protein


  Molecules made up of a series of amino acids bonded together
• Primary structure of a protein

  The initial sequence of amino acids
• Genes in DNA molecules

  Control protein structure and function by determining the exact sequence in which the amino acids join together when proteins are synthesised in a cell
• Triplet code


  The sequence of DNA nucleotide bases found within a gene is determined by a triplet (three-letter) code
• Codon


  Each sequence of three bases (i.e. each triplet of bases) in a gene codes for one amino acid
• Start and stop signals

  Triplets of bases that code for start (TAC - methionine) and stop signals, telling the cell where individual genes start and stop
• The genetic code is non-overlapping - each base is only read once in which codon it is part of
• Degenerate genetic code


  Multiple codons can code for the same amino acids
• The degenerate nature of the genetic code can limit the effect of mutations
• The genetic code is universal - the same triplet codes code for the same amino acids in all living things
• The universal nature of the genetic code is why genetic engineering (the transfer of genes from one species to another) is possible
• Anticodon


  The complementary sequence to the codon on mRNA, found on tRNA molecules that transfer amino acids