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 research and characterization.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( MW \) — Molecular weight of the protein (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: The equation accounts for the loss of one water molecule for each peptide bond formed during protein synthesis.

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., "MAKEL"). The sequence should contain only standard amino acid letters (A-Z, except B,J,O,U,X,Z).

5. Frequently Asked Questions (FAQ)

Q1: Why subtract water molecules?
A: During peptide bond formation, one water molecule is lost per bond, which must be accounted for in the total molecular weight.

Q2: What about modified amino acids?
A: This calculator uses standard amino acid weights. For modified residues (phosphorylated, acetylated, etc.), specialized calculators are needed.

Q3: How accurate is this calculation?
A: It provides a theoretical average molecular weight. Actual experimental values may differ slightly due to isotopic distributions.

Q4: What about N-terminal and C-terminal modifications?
A: This calculator assumes free amino and carboxyl termini. Additional modifications would require manual adjustment.

Q5: Can I use lowercase letters?
A: Yes, the calculator automatically converts to uppercase, but only standard amino acid letters are accepted.