1. What is Protein Molecular Mass?

The molecular mass 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 a fundamental property used in protein characterization and research.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( AA\_masses \) — Array of amino acid masses (g/mol)
• \( n \) — Number of amino acids in the sequence
• 18 — Molecular weight of water (g/mol)

Explanation: For each peptide bond formed, one water molecule is lost. A protein with n amino acids has n-1 peptide bonds.

3. Importance of Molecular Weight

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

4. Using the Calculator

Tips: Enter the amino acid sequence using standard one-letter codes (e.g., "GAVLIP"). The sequence should only contain valid amino acid codes.

5. Frequently Asked Questions (FAQ)

Q1: Does this include post-translational modifications?
A: No, this calculates the theoretical mass of the unmodified polypeptide chain.

Q2: What mass values are used?
A: Monoisotopic masses of amino acid residues (including H and OH termini).

Q3: How accurate is this calculation?
A: This gives the theoretical average mass. Actual mass may vary due to isotopes and modifications.

Q4: What about N-terminal modifications?
A: This assumes standard N-terminal H and C-terminal OH. For other termini, manual adjustment is needed.

Q5: Can I calculate mass for modified amino acids?
A: This calculator only handles standard amino acids. For modifications, specialized tools are needed.