Protein Mass Calculator Expasy

Protein Mass Calculation:

\[ MW (Da) = \text{Expasy sequence sum} \]

Molecular Weight:

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1. What is Protein Molecular Weight Calculation?

Protein molecular weight calculation determines the mass of a protein based on its amino acid sequence. This calculator uses the Expasy method which sums the monoisotopic masses of individual amino acids plus the mass of a water molecule.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ MW (Da) = \sum(\text{amino acid masses}) + 18.01056 \]

Where:

Each amino acid has a specific monoisotopic mass
18.01056 Da represents the mass of a water molecule (H₂O)
The sum includes all amino acids in the protein sequence

Explanation: The calculation accounts for the exact mass of each amino acid residue and adds the mass of water that is lost during peptide bond formation but present in the complete protein.

3. Importance of Protein Mass Calculation

Details: Accurate protein mass calculation is essential for protein identification, characterization, and various biochemical applications including mass spectrometry, electrophoresis, and chromatography.

4. Using the Calculator

Tips: Enter the protein amino acid sequence using single-letter codes. The sequence should not contain spaces or non-amino acid characters for accurate calculation.

5. Frequently Asked Questions (FAQ)

Q1: What are monoisotopic masses?
A: Monoisotopic mass is the mass of a molecule calculated using the exact mass of the most abundant isotope of each element.

Q2: Why add water molecule mass?
A: The water mass accounts for the hydroxyl group at the C-terminus and the hydrogen at the N-terminus of the complete protein.

Q3: Does this calculator consider post-translational modifications?
A: No, this calculator provides the theoretical mass of the unmodified protein sequence. Modifications would require additional calculations.

Q4: What is the difference between monoisotopic and average mass?
A: Monoisotopic mass uses exact isotope masses while average mass uses weighted averages of all naturally occurring isotopes.

Q5: Can I use three-letter amino acid codes?
A: No, this calculator only accepts single-letter amino acid codes (A, R, N, D, C, E, Q, G, H, I, L, K, M, F, P, S, T, W, Y, V).