1. What is Molecular Weight Calculation?

The molecular weight (MW) of a peptide or protein is calculated by summing the masses of its constituent amino acids and subtracting the mass of water molecules lost during peptide bond formation (18.01528 g/mol per bond).

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( AA_{masses} \) — Array of amino acid masses (g/mol)
• \( n \) — Number of amino acids in the sequence
• 18 — Molecular weight of water (g/mol)

Explanation: Each peptide bond formation results in the loss of one water molecule (condensation reaction).

3. Importance of Molecular Weight

Details: Knowing the molecular weight is essential for protein quantification, electrophoresis, mass spectrometry, and biochemical experiments.

4. Using the Calculator

Tips: Enter amino acid sequence in three-letter code format separated by hyphens (e.g., GLY-ALA-SER). All amino acids must be valid three-letter codes.

5. Frequently Asked Questions (FAQ)

Q1: What format should I use for the sequence?
A: Use three-letter amino acid codes separated by hyphens (e.g., ALA-GLY-THR-PRO).

Q2: Does this include post-translational modifications?
A: No, this calculator only considers standard amino acids without modifications.

Q3: What about N-terminal or C-terminal groups?
A: This calculation assumes standard amino and carboxyl termini. Special modifications are not included.

Q4: Are disulfide bonds accounted for?
A: No, disulfide bonds between cysteine residues are not considered in this calculation.

Q5: What mass values are used?
A: Monoisotopic masses of the most common isotope of each element are used.