1. What is Peptide Molecular Weight?

The molecular weight of a peptide is the sum of the atomic masses of all atoms in the molecule, accounting for water molecules lost during peptide bond formation. It's essential for peptide synthesis, mass spectrometry, and biochemical research.

2. How Does the Calculator Work?

The calculator uses the peptide molecular weight formula:

Where:

• \( AA_{masses} \) — Array of amino acid residue masses (g/mol)
• \( n \) — Number of amino acids in the peptide
• 18 — Molecular weight of water (g/mol)

Explanation: The equation accounts for the loss of water molecules during peptide bond formation between amino acids.

3. Importance of Molecular Weight Calculation

Details: Accurate molecular weight is crucial for peptide synthesis, mass spectrometry analysis, protein sequencing, and biochemical research applications.

4. Using the Calculator

Tips: Enter the amino acid sequence using 3-letter codes separated by hyphens, spaces, or commas (e.g., GLY-ALA-SER or GLY ALA SER). All amino acids must be valid 3-letter codes.

5. Frequently Asked Questions (FAQ)

Q1: What molecular weight does this calculate?
A: This calculates the average molecular weight (chemical MW) based on standard atomic weights, not monoisotopic mass.

Q2: Does this include post-translational modifications?
A: No, this calculates the molecular weight of the unmodified peptide chain only.

Q3: Why subtract (n-1)*18?
A: Each peptide bond formation results in the loss of one water molecule (H₂O, MW=18).

Q4: What about terminal groups?
A: This calculation assumes neutral termini (NH₂ and COOH). For specific end groups, additional adjustments are needed.

Q5: Can I use 1-letter amino acid codes?
A: This calculator requires 3-letter codes for clarity and to avoid ambiguity.