1. What is Molecular Weight Calculation?

The molecular weight of a protein or peptide is calculated by summing the molecular weights of its constituent amino acids and accounting for any modifications. This calculator provides the theoretical molecular weight based on the input sequence.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( MW \) — Molecular weight (g/mol)
• \( MW_{aa} \) — Molecular weight of each amino acid
• \( \text{adjustments} \) — Modifications like acetylation or amidation

Explanation: The calculation starts with water (H2O) for peptide bond formation, adds each amino acid's weight, and applies any terminal modifications.

3. Importance of Molecular Weight

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

4. Using the Calculator

Tips: Enter the amino acid sequence in single-letter code (case insensitive). Select any terminal modifications if applicable. The sequence should only contain standard amino acid letters.

5. Frequently Asked Questions (FAQ)

Q1: Why does the calculation start with water?
A: The water accounts for the formation of peptide bonds (loss of water during polymerization).

Q2: Are modified amino acids included?
A: This calculator only handles standard amino acids and basic terminal modifications.

Q3: How accurate is this calculation?
A: This provides the theoretical average molecular weight. Actual mass may vary slightly due to isotopic distribution.

Q4: Can I calculate molecular weight for RNA/DNA?
A: This calculator is for amino acid sequences. Different calculators exist for nucleic acids.

Q5: What about disulfide bonds?
A: Disulfide bonds reduce molecular weight by 2.02 g/mol per bond (loss of 2H).