1. What is Protein Molecular Weight?

Protein molecular weight (MW) is the sum of the masses of all atoms in a protein molecule, typically expressed in Daltons (Da) or grams per mole (g/mol). It's calculated by summing the weights of constituent amino acids minus water molecules lost during peptide bond formation.

2. How Does the Calculator Work?

The calculator uses the protein MW formula:

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: The equation accounts for the loss of one water molecule for each peptide bond formed during protein synthesis.

3. Importance of Protein MW Calculation

Details: Knowing a protein's MW is essential for gel electrophoresis, mass spectrometry, protein purification, and biochemical experiments.

4. Using the Calculator

Tips: Enter the protein sequence using single-letter amino acid codes (e.g., "MAHLE"). The sequence should only contain 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, so we subtract 18 g/mol for each bond.

Q2: Does this include post-translational modifications?
A: No, this calculates only the unmodified polypeptide chain. PTMs would add additional mass.

Q3: How accurate is this calculation?
A: It's accurate for the polypeptide backbone but doesn't account for disulfide bonds or modifications.

Q4: What about N-terminal and C-terminal groups?
A: This assumes standard amino and carboxyl termini. Special end groups would require adjustment.

Q5: Can I calculate MW for non-standard amino acids?
A: This calculator only handles the 20 standard amino acids. Non-standard residues require custom weights.