1. What is Peptide Molecular Weight?

The molecular weight of a peptide is the sum of the atomic weights of all atoms in the molecule, minus the weight of water molecules lost during peptide bond formation. It's essential for peptide synthesis, mass spectrometry analysis, and biochemical research.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( \sum \text{amino acids} \) — Sum of individual amino acid molecular weights
• \( n \) — Number of amino acids in the peptide
• 18 — Molecular weight of water (H₂O) lost per peptide bond

Explanation: Each peptide bond formation results in the loss of one water molecule (18 Da). For a peptide with n amino acids, there are (n-1) peptide bonds.

3. Importance of Peptide MW Calculation

Details: Accurate molecular weight calculation is crucial for mass spectrometry analysis, peptide synthesis planning, protein sequencing, and biochemical research applications.

4. Using the Calculator

Tips: Enter the peptide sequence using one-letter amino acid codes (e.g., "GAS" or "G-A-S" for Gly-Ala-Ser). The calculator automatically removes hyphens and converts to uppercase.

5. Frequently Asked Questions (FAQ)

Q1: Does this calculator account for modified amino acids?
A: No, this calculator only handles standard amino acids. For modified residues, you would need to manually adjust the weights.

Q2: Is this monoisotopic or average molecular weight?
A: The calculator uses monoisotopic weights (most abundant natural isotope of each element).

Q3: How are N-terminal and C-terminal groups handled?
A: The calculation assumes standard -NH₂ and -COOH termini. Special modifications would require adjustment.

Q4: What about disulfide bonds?
A: Disulfide bonds between cysteines are not accounted for in this basic calculator.

Q5: Can I calculate molecular weight for proteins?
A: Yes, but for very large proteins, other methods may be more practical due to potential post-translational modifications.