1. What is Protein Molecular Weight?

Protein molecular weight is the sum of the atomic weights of all atoms in a protein molecule, typically expressed in Daltons (Da). It's a fundamental property used in protein characterization, purification, and analysis.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( MW \) — Molecular weight in Daltons
• \( amino\ acid_i \) — Each amino acid in the sequence
• \( n \) — Total number of amino acids

Explanation: The calculator sums the molecular weights of each amino acid in the sequence using standard monoisotopic masses.

3. Importance of Molecular Weight Calculation

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

4. Using the Calculator

Tips: Enter the protein sequence using single-letter amino acid codes (e.g., "MALWMRLLPLLALLALWGPDPAAAFVNQHLCGSHLVEALYLVCGERGFFYTPKT"). The sequence should contain only valid amino acid codes.

5. Frequently Asked Questions (FAQ)

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

Q2: Does this include post-translational modifications?
A: No, this calculator provides the molecular weight of the unmodified polypeptide chain only.

Q3: What about the N-terminal methionine?
A: The calculator includes all amino acids in the sequence provided, including any initial methionine.

Q4: Are water molecules accounted for in the calculation?
A: Yes, the amino acid weights already account for water loss during peptide bond formation.

Q5: How accurate is this calculation?
A: This provides a theoretical molecular weight based on monoisotopic masses. Actual experimental values may vary slightly.