Protein Molecular Mass Calculator

Molecular Weight Formula:

\[ MW = \sum AA_{MW} - (n-1) \times 18 \]

Molecular Weight:

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is Protein Molecular Mass?

Protein molecular mass refers to the mass of a protein molecule, typically measured in Daltons (Da) or g/mol. It's calculated by summing the masses of all amino acids in the protein chain and subtracting the mass of water molecules lost during peptide bond formation.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ MW = \sum AA_{MW} - (n-1) \times 18 \]

Where:

\( MW \) — Molecular weight (g/mol)
\( \sum AA_{MW} \) — Sum of individual amino acid molecular weights
\( n \) — Number of amino acid residues
18 — Molecular weight of water (g/mol)

Explanation: Each peptide bond formation releases one water molecule, so (n-1) water molecules are subtracted from the total amino acid mass.

3. Importance of Molecular Weight Calculation

Details: Accurate molecular weight calculation is essential for protein characterization, gel electrophoresis, mass spectrometry, protein purification, and biochemical research applications.

4. Using the Calculator

Tips: Enter the amino acid sequence using single-letter codes (A, R, N, D, C, Q, E, G, H, I, L, K, M, F, P, S, T, W, Y, V). The sequence should contain only valid amino acid characters.

5. Frequently Asked Questions (FAQ)

Q1: Why subtract water molecules?
A: During peptide bond formation, a water molecule is released for each bond created. This water loss must be accounted for in the final molecular weight calculation.

Q2: Are modified amino acids supported?
A: This calculator uses standard amino acid weights. For modified amino acids, manual adjustment of weights would be required.

Q3: What about N-terminal and C-terminal modifications?
A: This calculator assumes standard amino and carboxyl termini. Additional modifications would require manual adjustment of the calculated weight.

Q4: How accurate is this calculation?
A: The calculation provides the theoretical average molecular weight. Actual experimental values may vary slightly due to isotopic distributions.

Q5: Can I calculate molecular weight for peptides?
A: Yes, this calculator works for both peptides and proteins using the same formula.