1. What is Peptide Molecular Weight?

The molecular weight (MW) of a peptide or protein is the sum of the masses of its amino acid residues minus the mass of water molecules lost during peptide bond formation. It's expressed in Daltons (Da).

2. How Does the Calculator Work?

The calculator uses the following formula:

Where:

• \( \sum(residues) \) — Sum of individual amino acid masses
• \( n \) — Number of amino acids in the sequence
• \( water \) — 18.01528 Da (mass of one water molecule)

Explanation: For each peptide bond formed, one water molecule is lost. The calculator sums the amino acid masses and subtracts water for each peptide bond.

3. Importance of Molecular Weight

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

4. Using the Calculator

Tips: Enter the amino acid sequence in single-letter code (e.g., "GAMMA"). The sequence is case-insensitive and spaces are automatically removed.

5. Frequently Asked Questions (FAQ)

Q1: What molecular weight does this calculate?
A: This calculates the monoisotopic molecular weight of the peptide chain without any modifications or terminal groups.

Q2: Does this include post-translational modifications?
A: No, this calculates only the unmodified peptide chain. Modifications like phosphorylation or glycosylation need to be calculated separately.

Q3: What about N-terminal and C-terminal groups?
A: This calculation assumes standard -H and -OH termini. For other terminal groups (e.g., acetylation), additional calculations are needed.

Q4: What if my sequence contains non-standard amino acids?
A: The calculator only recognizes standard 20 amino acids. Non-standard residues will cause an error.

Q5: How accurate is this calculation?
A: The calculation uses monoisotopic masses and is theoretically precise, though actual measurements may vary slightly due to isotopic distributions.