- Gene (DNA coded for a polypeptide/protein) is a unit of inheritance
- 4 nucleotides : UCGA
- 20 standard amino acids
- triplet combination : 4x4x4 = 64 different sequences / codons
- base sequences of mRNA; reading 5' to 3'
Features of genetic code
- 3 nonsense / terminator codons (UAA, UAG, UGA) - specify termination of protein synthesis.
- 2 amino acids represented by a single codon (Met, Trp)
- start codon is AUG (Met)
- degenerate - 2 or more synonymous codons code for any particular amino acids
- universality - the same codons stand for the same amino acids in viruses and all organisms from bacteria to higher eukaryotes.
- non-overlapping coding
degeneracy and wobble hypothesis
- 1st 2 bases are constant. 3rd vary.
- do not require 61 aminoacyl-tRNAs
- Wobble hypothesis - formation of nonstandard base pair between the 3' terminal position of codons and the 5' terminal positions of anticodons.