Research and documentation scope
Educational laboratory information only. No medical advice, dosing, injection, administration or personal-use guidance.
Sequence defines the residue order
A peptide sequence records amino acids from the N-terminus to the C-terminus. Swapping two residues creates a different sequence even if the total elemental composition and nominal mass remain unchanged.
Terminal groups and modifications
Amidation, acetylation, cyclisation, disulfide bonds, lipidation and non-natural residues alter the expected structure and often the mass. A common name that omits these features is analytically incomplete.
Monoisotopic versus average mass
Reports may use monoisotopic mass, average molecular weight, neutral mass or an observed mass-to-charge value. Charge states and adducts must be interpreted before comparing a spectral peak with a theoretical number.
Why mass is not the whole identity
Isomers, residue-order variants and some modifications can produce indistinguishable nominal masses. Retention behaviour, fragmentation or other orthogonal evidence may be needed where those alternatives matter.
Frequently asked questions
Can two peptides have the same molecular weight?
Yes. Different residue orders or isomeric structures can share the same composition and mass.
What does m/z mean?
It is mass-to-charge ratio, the quantity measured for ions in mass spectrometry.
Related external reading:
- ZENTRA testing methods overviewexternal · supplier educational page
Editorial reference only; not an endorsement.