1. What is a Protein Molecular Weight Calculator?

Definition: This calculator estimates the molecular weight of a protein based on its amino acid sequence.

Purpose: It helps researchers, biochemists, and students determine the molecular weight of proteins for experimental design and analysis.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( MW \) — Molecular weight (Daltons, Da)
• \( M_i \) — Molecular weight of amino acid i (Da)
• \( n_i \) — Number of amino acid i (dimensionless)

Explanation: The calculator sums the molecular weights of all amino acids in the sequence and subtracts the weight of water molecules lost during peptide bond formation.

3. Importance of Molecular Weight Calculation

Details: Knowing a protein's molecular weight is crucial for SDS-PAGE, chromatography, mass spectrometry, and other biochemical techniques.

4. Using the Calculator

Tips: Enter the protein sequence using single-letter amino acid codes (e.g., "MAKEG"). The sequence is case-insensitive.

5. Frequently Asked Questions (FAQ)

Q1: Why is water subtracted in the calculation?
A: For each peptide bond formed, one water molecule is lost (condensation reaction).

Q2: Does this include post-translational modifications?
A: No, this calculates only the unmodified polypeptide chain's molecular weight.

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

Q4: How accurate is this calculation?
A: It provides a theoretical average molecular weight based on amino acid composition.

Q5: What if my protein has non-standard amino acids?
A: This calculator only handles the 20 standard amino acids. Non-standard residues will cause an error.