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. It's typically expressed in Daltons (Da) or kilodaltons (kDa).

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( \sum(AA) \) — Sum of amino acid masses
• \( 18 \) — Mass of water lost per peptide bond (18.01528 Da)
• \( n \) — Number of amino acids in the sequence

Explanation: Each peptide bond formation results in the loss of one water molecule (H₂O), so for a protein with n amino acids, there are (n-1) peptide bonds.

3. Importance of Molecular Weight Calculation

Details: Knowing a protein's molecular weight is essential for protein characterization, gel electrophoresis, mass spectrometry, chromatography, and many other biochemical applications.

4. Using the Calculator

Tips: Enter the protein sequence using single-letter amino acid codes (case insensitive). The calculator automatically removes any non-amino acid characters before calculation.

5. Frequently Asked Questions (FAQ)

Q1: Does this include post-translational modifications?
A: No, this calculator only computes the molecular weight of the unmodified polypeptide chain.

Q2: What about N-terminal or C-terminal modifications?
A: The calculation assumes standard amino and carboxyl termini. Special modifications are not included.

Q3: How accurate is this calculation?
A: It's accurate for theoretical calculations using monoisotopic masses. Actual experimental values may vary slightly.

Q4: Can I use three-letter amino acid codes?
A: No, only single-letter codes are accepted by this calculator.

Q5: What about selenocysteine (U) or pyrrolysine (O)?
A: These uncommon amino acids are not included in the current calculation.