Methionine Amino Acid Code (Met, M)

Protein sequences usually use one-letter codes because they are compact. In that notation, Mmeans Methionine. The three-letter code Met is easier to read in structure notes, mutation descriptions, and teaching materials.

Codons are different from amino acid letter codes. A codon is a three-base RNA word read during translation, while an amino acid code is the protein shorthand. The codons AUG all point to Methioninein the standard genetic code.

The Methionine amino acid is classified here as sulfur-containing. That label is a shortcut for first-pass interpretation, not a complete description of every chemical behavior.

Methionine is often checked because hydrophobic residues tend to be important in protein cores, membranes, and folded structural regions. The exact effect depends on protein context, neighboring residues, pH, solvent exposure, and the folded state of the whole protein.

In a protein sequence, Methionine is usually discussed as an amino acid residue. That means the amino acid has been incorporated into a peptide chain and has lost the atoms removed during peptide bond formation. The one-letter code M and three-letter code Met refer to that residue in sequence notation.

The listed molecular weight is for the free amino acid. Protein mass calculations often use residue masses instead, because water is removed when peptide bonds form.

Do not confuse the one-letter code M with a DNA or RNA base. It is an amino acid symbol, not a nucleotide in a codon.

Do not read codons without checking the frame. A triplet that encodes Methionine in one frame may disappear in another frame. For gene design, check organism-specific codon usage after confirming the basic amino acid identity.