The genetic code

• What is a gene?

  A section of DNA that contains the coded information for making polypeptides and functional RNA
• What is a locus?

  A particular point on a section of DNA
• The gene is a base sequence that codes for:

  • The amino acid sequence of a polypeptide
  • rRNA and tRNA
• The genetic code:

  • 3 bases for each amino acid, called a triplet
  • 64 possible triplets
  • 20 amino acids
• Degenerate:

  • more than one triplet can code for the same amino acid
• A triplet is always read in a particular direction along the DNA strand
• Stop codes:

  • mark the end of a polypeptide chain
• Non-overlapping:

  • the code is read in triplets
  • 123, 456. Not 123, 234
• Universal:

  • the code is the same in every organism