Protein Molecular Weight Calculator kDa

Protein Molecular Weight Formula:

\[ MW = \frac{\sum(AA_{masses})}{1000} - (n-1) \times 0.018 \]

Molecular Weight (MW):

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1. What is Protein Molecular Weight?

The molecular weight (MW) of a protein is the sum of the masses of its amino acid residues minus the mass of water molecules lost during peptide bond formation. It's typically reported in kilodaltons (kDa).

2. How Does the Calculator Work?

The calculator uses the protein MW formula:

\[ MW = \frac{\sum(AA_{masses})}{1000} - (n-1) \times 0.018 \]

Where:

\( AA_{masses} \) — Array of amino acid masses (g/mol)
\( n \) — Number of amino acid residues
0.018 — Mass of one water molecule (kDa)

Explanation: The formula accounts for water molecules lost during peptide bond formation (n-1 bonds) and converts the result to kDa.

3. Importance of Molecular Weight Calculation

Details: Knowing a protein's MW is essential for SDS-PAGE analysis, protein purification, concentration determination, and biochemical experiments.

4. Using the Calculator

Tips: Enter amino acid masses as comma-separated values in g/mol. The number of residues should match the count of amino acid masses entered.

5. Frequently Asked Questions (FAQ)

Q1: Why subtract water molecules?
A: For each peptide bond formed, one water molecule is lost (condensation reaction).

Q2: What are typical protein MW ranges?
A: Small proteins: 10-50 kDa, medium: 50-100 kDa, large: >100 kDa.

Q3: How accurate is this calculation?
A: It provides theoretical MW. Post-translational modifications may affect actual MW.

Q4: Should I include N-terminal methionine?
A: Yes, unless it's known to be cleaved post-translationally.

Q5: What about disulfide bonds?
A: Disulfide bonds don't affect MW calculation as no atoms are lost/gained.