1. What is Protein Molecular Weight?

The molecular weight (MW) of a protein is the sum of the masses of its amino acids minus the mass of water molecules lost during peptide bond formation (18.015 g/mol per bond).

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( MW \) — Molecular weight (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: For each peptide bond formed, one water molecule is lost, hence subtracting 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 experiments.

4. Using the Calculator

Tips: Enter the protein sequence in single-letter code (e.g., "MAEGEITTFT"). The calculator automatically removes spaces and converts to uppercase.

5. Frequently Asked Questions (FAQ)

Q1: What amino acid codes are supported?
A: Standard 20 amino acids in single-letter code (A, R, N, D, C, E, Q, G, H, I, L, K, M, F, P, S, T, W, Y, V).

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

Q3: Why subtract water molecules?
A: Each peptide bond formation releases one water molecule during protein synthesis.

Q4: What about N-terminal or C-terminal modifications?
A: These are not accounted for in this basic calculation. You would need to add their masses separately.

Q5: How accurate is this calculation?
A: It provides the theoretical average molecular weight based on amino acid composition. Actual MW may vary slightly due to isotopic distribution.