1. What is Peptide Molecular Weight?

The molecular weight of a peptide is the sum of the atomic weights 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:

• \( MW \) — Molecular weight of peptide (g/mol)
• \( MW_{aa} \) — Molecular weight of each amino acid (g/mol)
• \( length \) — Number of amino acids in the sequence
• 18 — Molecular weight of water (g/mol)

Explanation: Each peptide bond formation results in the loss of one water molecule (H₂O, MW=18 g/mol).

3. Importance of Molecular Weight Calculation

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

4. Using the Calculator

Tips: Enter the peptide sequence using either 1-letter codes (e.g., GAS) or 3-letter codes separated by hyphens (e.g., GLY-ALA-SER). The calculator automatically detects the format.

5. Frequently Asked Questions (FAQ)

Q1: What amino acid codes are supported?
A: Both 1-letter (A, R, N, D, etc.) and 3-letter (ALA, ARG, ASN, ASP, etc.) codes are supported.

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

Q3: Why subtract water molecules?
A: For each peptide bond formed, one water molecule is lost (condensation reaction).

Q4: How accurate is this calculation?
A: It provides the theoretical average molecular weight based on standard atomic weights.

Q5: Can I calculate mass for cyclic peptides?
A: For cyclic peptides, you would need to subtract one additional water molecule for the cyclization.