1. What is Peptide/Protein Molecular Weight?

Molecular weight calculation for peptides and proteins is essential in biochemistry and pharmaceutical research. It represents the sum of atomic weights of all atoms in a molecule, minus the weight of water molecules lost during peptide bond formation.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( MW \) — Molecular weight (g/mol)
• \( \sum AA_{MW} \) — Sum of amino acid molecular weights
• \( n \) — Number of amino acid residues
• 18 — Molecular weight of water (g/mol)

Explanation: The formula accounts for water molecules lost during peptide bond formation between amino acids.

3. Importance of Molecular Weight Calculation

Details: Accurate molecular weight determination is crucial for protein characterization, drug development, mass spectrometry analysis, and biochemical research applications.

4. Using the Calculator

Tips: Enter amino acid sequence using standard three-letter codes (e.g., GLY-ALA-SER). Separate residues with hyphens, commas, or spaces. All amino acid codes must be valid.

5. Frequently Asked Questions (FAQ)

Q1: Why subtract (n-1)×18 in the formula?
A: This accounts for the water molecules (MW = 18 g/mol) lost during the formation of each peptide bond between amino acids.

Q2: What are the standard amino acid codes?
A: Standard three-letter codes include ALA, ARG, ASN, ASP, CYS, GLN, GLU, GLY, HIS, ILE, LEU, LYS, MET, PHE, PRO, SER, THR, TRP, TYR, VAL.

Q3: Does this calculator account for modified amino acids?
A: No, this calculator uses standard amino acid molecular weights. Modified residues require specialized calculations.

Q4: What about terminal groups?
A: This calculation provides the molecular weight of the peptide chain without special terminal modifications.

Q5: Can I calculate molecular weight for very large proteins?
A: While theoretically possible, extremely long sequences may exceed practical limits for this calculator.