1. What is Protein Molecular Weight?

The molecular weight (MW) of a protein is the sum of the masses of all its amino acids minus the mass of water molecules lost during peptide bond formation. It's a fundamental property used in protein characterization and experimental design.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( amino\_acid\_masses \) — Mass of each amino acid in the sequence (Da)
• \( n \) — Number of amino acid residues
• 18 — Mass of water lost per peptide bond (Da)

Explanation: The equation accounts for the condensation reaction that forms peptide bonds, where one water molecule is lost for each bond formed.

3. Importance of Molecular Weight Calculation

Details: Knowing a protein's MW is essential for SDS-PAGE, mass spectrometry, chromatography, and determining molar concentrations for experiments.

4. Using the Calculator

Tips: Enter the protein sequence in single-letter code (case insensitive). The calculator will ignore invalid characters and spaces.

5. Frequently Asked Questions (FAQ)

Q1: What mass values are used for amino acids?
A: The calculator uses monoisotopic masses of amino acid residues (without water).

Q2: Does this include post-translational modifications?
A: No, this calculates the theoretical MW of the unmodified polypeptide chain.

Q3: How accurate is this calculation?
A: It's accurate for theoretical MW. Actual experimental MW may differ due to isotopes and modifications.

Q4: What about N-terminal methionine cleavage?
A: This isn't accounted for. You should edit the sequence manually if needed.

Q5: Can I calculate MW for multiple chains?
A: For multi-chain proteins, calculate each chain separately and sum the results.