1. What is Protein Molecular Weight?

The molecular weight (MW) of a protein is the sum of the masses of all its amino acid residues plus the mass of one water molecule (for the N-terminal H and C-terminal OH). It's typically expressed in Daltons (Da).

2. How Does the Calculator Work?

The calculator uses the following formula:

Where:

• \( AA \) — Amino acid residues (using monoisotopic masses)
• \( H_2O \) — Water molecule (18.015 Da)

Explanation: The calculation sums the weights of all amino acids in the sequence plus one water molecule (for the terminal groups).

3. Importance of Molecular Weight

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

4. Using the Calculator

Tips: Enter the protein sequence in single-letter code (case insensitive). The calculator automatically removes non-amino acid characters.

5. Frequently Asked Questions (FAQ)

Q1: What amino acid codes are supported?
A: Standard 20 amino acids (A, C, D, E, F, G, H, I, K, L, M, N, P, Q, R, S, T, V, W, Y).

Q2: Are modified amino acids included?
A: No, this calculator uses only standard amino acid masses. For modified residues, specialized tools are needed.

Q3: What's the difference between monoisotopic and average mass?
A: Monoisotopic mass uses the most abundant isotope for each element, while average mass considers natural isotope distribution. This calculator uses monoisotopic masses.

Q4: How accurate is this calculation?
A: For theoretical purposes, it's very accurate. For experimental work, consider post-translational modifications and other factors.

Q5: Can I calculate molecular weight from DNA sequence?
A: No, this calculator requires protein sequence. You'd need to translate DNA to protein first.