1. What is Peptide Molecular Weight?

Peptide molecular weight is the sum of the atomic weights of all atoms in a peptide molecule. For serum peptides, this calculation accounts for the loss of water molecules during peptide bond formation.

2. How Does the Calculator Work?

The calculator uses the following formula:

Where:

• \( MW \) — Molecular weight (g/mol)
• \( MW_{aa} \) — Amino acid residue weight (g/mol)
• \( length \) — Number of amino acids in the peptide

Explanation: The formula accounts for the loss of one water molecule (18 g/mol) for each peptide bond formed between amino acids.

3. Importance of Peptide MW Calculation

Details: Knowing the molecular weight is essential for peptide quantification, solubility predictions, mass spectrometry analysis, and biochemical applications.

4. Using the Calculator

Tips: Enter the peptide sequence using single-letter amino acid codes (e.g., "GYWHHY"). The sequence should contain only standard 20 amino acids.

5. Frequently Asked Questions (FAQ)

Q1: Why subtract 18*(length-1) in the formula?
A: This accounts for water molecules lost during peptide bond formation (condensation reaction) between amino acids.

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

Q3: How accurate is this calculation?
A: It provides theoretical average molecular weight. For exact mass, isotopic distribution should be considered.

Q4: Can I use lowercase letters for the sequence?
A: Yes, the calculator automatically converts to uppercase.

Q5: What about non-standard amino acids?
A: This calculator only handles the 20 standard amino acids. Special residues require manual calculation.