A codon is a three-letter “word” in DNA or RNA that tells the cell which amino acid to add to a growing protein, or when to start or stop making that protein.

Simple definition

  • A codon is a sequence of three nucleotides (bases) in DNA or RNA, such as AUG or GCU.
  • Each codon corresponds to one specific amino acid, or acts as a start or stop signal during protein synthesis.

Where codons are found

  • Codons appear along genes in DNA and in the messenger RNA (mRNA) copied from those genes.
  • During translation , ribosomes read mRNA codons in order to assemble amino acids into a protein chain.

How many codons exist

  • There are 64 possible codons made from combinations of the four bases (A, U/T, G, C) taken three at a time.
  • Of these, 61 codons specify the 20 standard amino acids, and 3 are stop codons that signal the end of the protein.

Special codons

  • A start codon (often AUG in mRNA) tells the ribosome where to begin building the protein and also codes for the amino acid methionine.
  • Stop codons (such as UAA, UAG, UGA in mRNA) do not code for amino acids; they instruct the ribosome to release the completed protein.

Why codons matter today

  • Modern genetics, from understanding inherited diseases to designing mRNA vaccines, relies on reading and editing codons to control which proteins cells make.
  • Changes (mutations) in codons can alter amino acids, sometimes causing disease, but they can also be used deliberately in biotechnology to engineer new or improved proteins.

Information gathered from public forums or data available on the internet and portrayed here.