The Genetic Code

The Genetic Code

  • The genetic code is the set of rules that dictates how a sequence of nucleotides in DNA codes for specific amino acids to produce proteins.
  • It is a triplet code where three bases (codon) on the mRNA strand corresponds to a specific amino acid.
  • The genetic code is universal, all organisms (with rare exceptions) use the same code which suggests a common evolutionary origin.
  • The genetic code is ambiguous, meaning each codon codes for only one amino acid. This prevents errors in protein synthesis.

Characteristics of Genetic Code

  • Redundancy: More than one codon can code for a single amino acid. This is called redundancy or degeneracy, which acts as a buffer against mutations resulting in changes in protein sequences.
  • Initiation codon: AUG is the start codon, and it codes for the amino acid methionine.
  • Termination codons: There are three stop codons (UAA, UAG, UGA) that do not code for an amino acid and signal the end of protein synthesis.

Reading the Genetic Code

  • The genetic code is read by mRNA, from the 5’ end to the 3’ end, in a successive and non-overlapping manner.
  • Any alteration in the normal reading sequence such as deletions or additions can cause frameshift mutations, leading to an entirely different set of amino acids being coded and potentially dysfunctional proteins.

Codon Usage

  • Codon usage varies among species which is known as codon bias. This aids the organism in regulating gene expression.
  • Certain codons are preferred over others for the same amino acids, a phenomenon observed due to variations in tRNA populations in different organisms.