1. What is Protein Molecular Weight?

The molecular weight of a protein is the sum of the weights of its amino acids minus the weight of water molecules lost during peptide bond formation. It's a fundamental property used in protein analysis and characterization.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

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

Explanation: Each peptide bond formation removes one water molecule (18 g/mol), so we subtract 18×(n-1) where n is the number of amino acids.

3. Importance of Molecular Weight Calculation

Details: Knowing a protein's molecular weight is essential for gel electrophoresis, mass spectrometry, protein purification, and biochemical characterization.

4. Using the Calculator

Tips: Enter the protein sequence using single-letter amino acid codes (e.g., "MAEGEITTFT"). The sequence should only contain standard amino acid letters (A-Z, except B,J,O,U,X,Z).

5. Frequently Asked Questions (FAQ)

Q1: Does this include post-translational modifications?
A: No, this calculates the theoretical molecular weight of the unmodified polypeptide chain.

Q2: What about N-terminal methionine cleavage?
A: The calculator assumes the sequence exactly as entered. You must account for any processing manually.

Q3: How accurate is this calculation?
A: It's accurate for theoretical calculations but actual experimental values may differ due to factors like isotopic distribution.

Q4: Can I use lowercase letters?
A: Yes, the calculator automatically converts to uppercase.

Q5: What about non-standard amino acids?
A: This calculator only handles the 20 standard amino acids. Special residues require manual adjustment.