1. What is Oligopeptide Molecular Weight?

The molecular weight of an oligopeptide is the sum of the atomic masses of all atoms in the molecule. For peptides, this includes the amino acid residues minus water molecules lost during peptide bond formation.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( AA_{masses} \) — Masses of individual amino acid residues
• \( n \) — Number of amino acids in the sequence
• 18 — Molecular weight of water (lost in each peptide bond)

Explanation: The calculator sums the masses of all amino acids in the sequence, then subtracts the mass of water for each peptide bond formed (n-1 bonds).

3. Importance of Molecular Weight Calculation

Details: Knowing the molecular weight is essential for peptide synthesis, purification, mass spectrometry analysis, and biochemical applications.

4. Using the Calculator

Tips: Enter the amino acid sequence using standard one-letter codes separated by hyphens (e.g., GLY-ALA-SER or G-A-S). The calculator is case-insensitive.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between oligopeptide and polypeptide?
A: Oligopeptides typically contain 2-20 amino acids, while polypeptides are longer chains (up to proteins with thousands of residues).

Q2: Are modifications like phosphorylation included?
A: No, this calculator only computes the unmodified peptide weight. Post-translational modifications require additional calculations.

Q3: Which mass is calculated - average or monoisotopic?
A: This calculator uses monoisotopic masses (most abundant natural isotope for each element).

Q4: How are N-terminal and C-terminal groups handled?
A: The calculation assumes standard -NH2 and -COOH termini unless otherwise specified.

Q5: What about disulfide bonds?
A: Disulfide bonds between cysteines are not accounted for in this basic calculator.