1. What is Protein Molecular Weight?

The molecular weight 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 research and characterization.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( \sum AA\ MW \) — Sum of individual amino acid molecular weights
• \( n \) — Number of amino acids in the sequence
• 18 — Molecular weight of water (lost per peptide bond formed)

Explanation: For each peptide bond formed, one water molecule is lost (condensation reaction). The formula accounts for this by subtracting (n-1) water molecules.

3. Importance of Molecular Weight Calculation

Details: Knowing a protein's molecular weight is essential for SDS-PAGE, mass spectrometry, protein purification, concentration determination, and biochemical experiments.

4. Using the Calculator

Tips: Enter the amino acid sequence using standard 3-letter codes (e.g., GLY-ALA-SER). You can separate amino acids with spaces, commas, or hyphens. The calculator is case-insensitive.

5. Frequently Asked Questions (FAQ)

Q1: Why subtract water molecules?
A: Each peptide bond formation results in the loss of one water molecule (condensation reaction). For n amino acids, there are (n-1) peptide bonds.

Q2: Does this include post-translational modifications?
A: No, this calculator only considers the polypeptide chain. PTMs like phosphorylation or glycosylation would add additional mass.

Q3: What about N-terminal and C-terminal groups?
A: This calculation assumes standard protonated N-terminus and deprotonated C-terminus at physiological pH.

Q4: How accurate is this calculation?
A: It provides theoretical average molecular weight. Actual mass may vary slightly due to isotopic distributions.

Q5: Can I use 1-letter codes?
A: Currently only 3-letter codes are supported for unambiguous identification.