8.1. Genes and the Triplet Code

avatar
Created by
Emma Russell

Cards (16)

  • Polypeptides make up proteins, enzymes are proteins and because enzymes control chemical reactions they're responsible for an organisms development and activities
  • Genome: The complete collection of an organisms genes
  • Proteome: All the proteins in an organism
  • Only 20 different amino acids regularly occur in proteins. Meaning each amino acid must have it's own code of bases on the DNA, and only four bases are present in DNA
  • If each base on the DNA coded for a different amino acid, only 4 amino acids would be coded for.
  • If bases were coded for in pairs, only 16 possible codes would be possible. Whereas if bases were coded in triplets, 64 possible codes would be possible. Which is enough for all the possible codes for amino acids to be satisfied.
  • DNA codes for amino acids but DNA is made up of nucleotides. DNA is NOT made up of amino acids
  • The genetic code is degenerate because there are more codons than amino acids. This means that some amino acids can be represented by multiple codons. For example, leucine has six codons (UUA, UUG, CUU, CUC, CUA, CUG)
  • A few amino acids are coded for with only a single triplet. Whereas the majority of amino acids are coded for by 2 to 6 triplets.
  • A triplet is always read in one particular direction along the DNA strand.
  • The start of a DNA sequence codes for polypeptides is always the same triplet. Stop codons mark the end of a polypeptide chain, and they do not count as an amino acid
  • The genetic code is non-overlapping which means that each base is ONLY ever read ONCE
  • The genetic code is universal, with only a few minor exceptions, each triplet codes for the same amino acid in all organisms. Which is indirect evidence for evolution
  • Three adjacent nucleotides = codon = codes for amino acid
  • The codon AUG codes for methionine and is found at the beginning of every mRNA, indicating the start of a protein.
  • Methionine and Trytophan are the only two amino acids that are coded for by only a single codon.
    AUG is Methionine
    UGG is Trytophan