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 research.

2. How Does the Calculator Work?

The calculator uses the protein molecular weight equation:

Where:

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

Explanation: For each peptide bond formed, one water molecule is lost (condensation reaction). Therefore, for a protein with n amino acids, there are (n-1) peptide bonds and (n-1) water molecules to subtract.

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., "MAKEGT"). The sequence should contain only valid amino acid characters (A, R, N, D, C, Q, E, G, H, I, L, K, M, F, P, S, T, W, Y, V).

5. Frequently Asked Questions (FAQ)

Q1: Why subtract water molecules?
A: During protein synthesis, each peptide bond formation releases one water molecule, so these must be accounted for in the total weight.

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

Q3: What about N-terminal and C-terminal groups?
A: This calculation assumes standard protonated N-terminus and deprotonated C-terminus at physiological pH.

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

Q5: Can I use lowercase letters for the sequence?
A: Yes, the calculator automatically converts to uppercase.