1. What is Protein Molecular Weight?

Protein molecular weight is the sum of the masses of all amino acids in the protein minus the mass 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 MW equation:

Where:

• \( AA\_masses \) — Molecular weights of individual amino acids (g/mol)
• \( n \) — Number of amino acids in the sequence
• 18 — Molecular weight of water (g/mol)

Explanation: Each peptide bond formation results in the loss of one water molecule (18 g/mol). For a protein with n amino acids, there are (n-1) peptide bonds.

3. Importance of Protein MW Calculation

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

4. Using the Calculator

Tips: Enter the protein sequence using single-letter amino acid codes (case insensitive). The calculator will ignore any non-amino acid characters.

5. Frequently Asked Questions (FAQ)

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

Q2: How accurate is this calculation?
A: It's accurate for the amino acid sequence entered, but actual experimental MW may vary due to modifications or measurement conditions.

Q3: What about N-terminal methionine cleavage?
A: The calculator assumes all entered amino acids are present in the mature protein.

Q4: Can I calculate MW for peptides?
A: Yes, the calculator works for peptides of any length (dipeptides and larger).

Q5: What units are used?
A: Molecular weight is calculated in grams per mole (g/mol).