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 various biochemical applications including protein characterization, purification, and analysis.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( MW \) — Molecular weight in daltons
• \( \sum (Molecular AA) \) — Sum of molecular weights of individual amino acids

Explanation: The calculation accounts for the molecular weight of each amino acid in the protein sequence and subtracts the weight of water molecules lost during peptide bond formation.

3. Importance of Molecular Weight Calculation

Details: Accurate molecular weight determination is essential for protein characterization, gel electrophoresis, mass spectrometry, chromatography, and understanding protein structure-function relationships.

4. Using the Calculator

Tips: Enter the protein sequence using single-letter amino acid codes (A, R, N, D, C, E, Q, G, H, I, L, K, M, F, P, S, T, W, Y, V). The sequence should not contain spaces or special characters.

5. Frequently Asked Questions (FAQ)

Q1: What are daltons (Da)?
A: A dalton is a unit of mass equal to 1/12 the mass of a carbon-12 atom, approximately 1.66053906660 × 10⁻²⁷ kilograms.

Q2: Does this calculator account for post-translational modifications?
A: No, this calculator provides the theoretical molecular weight based on the amino acid sequence only and does not account for modifications like phosphorylation or glycosylation.

Q3: Why subtract water molecular weight?
A: Water molecules are lost during peptide bond formation between amino acids, so we subtract 18.015 Da for each peptide bond in the protein.

Q4: What about N-terminal and C-terminal modifications?
A: This calculator assumes standard protonated N-terminal and deprotonated C-terminal groups. Special modifications are not considered.

Q5: How accurate is this calculation?
A: This provides a theoretical molecular weight that matches well with experimental techniques like mass spectrometry for unmodified proteins.