• A?triplet?is a sequence of three DNA bases that codes for a specific amino acid
• A?codon?is a sequence of three?mRNA?bases that codes for a specific amino acid
• A codon is transcribed from the triplet and is complementary to it
• An?anticodon?is a sequence of three?tRNA?bases that are complementary to a codon
• When comparing the genetic code to amino acid sequences, mRNA codons are often used
• The four bases found in RNA molecules (adenine, uracil, cytosine and guanine) have the ability to form?64?different codons
• The genetic code is?degenerate
  • Multiple mRNA codons can encode the same amino acid
  • This means that a?change in the genetic code doesn’t necessarily result in a change in the amino acid sequence
  • UGU and UGC both code for the amino acid cysteine

   

• Some send important signals to the transcription machinery
  • The?START?codon initiates the process of transcription and ensure it starts in the right location (this is always the amino acid methionine in eukaryotic cells, coded for by the codon AUG)
  • STOP?codons cause transcription to terminate and do not code for an amino acid e.g. UAA

   

• The genetic code is?non-overlapping
  • Each base is only read once in the codon it is part of

   

• The number of amino acids in a protein can be calculated using the number of coding nucleotides in the mRNA molecule and vice versa:
  • When given the number of coding mRNA nucleotides, divide by 3 and minus one (for the stop codon – it is best to state this in your answer too)
  • When given the number of amino acids, multiply by 3 and add three (for the stop codon)

   

mRNA Codons and Amino Acids Table