1. What is Molecular Weight of a Protein?

The molecular weight (MW) of a protein is the sum of the masses of its amino acids minus the mass of water molecules lost during peptide bond formation. It's an important parameter in protein characterization and experimental design.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( MW \) — Molecular weight of the protein (g/mol)
• \( MW_{aa} \) — Molecular weight of individual amino acids (g/mol)
• \( length \) — Number of amino acids in the sequence
• 18 — Molecular weight of water (g/mol)

Explanation: For each peptide bond formed, one water molecule is lost (condensation reaction). The formula accounts for this by subtracting 18 g/mol for each bond.

3. Importance of Molecular Weight Calculation

Details: Knowing a protein's molecular weight is essential for gel electrophoresis, chromatography, protein quantification, and many other biochemical techniques.

4. Using the Calculator

Tips: Enter the amino acid sequence in single-letter code (e.g., "MAKEGT"). The calculator is case-insensitive and ignores non-letter characters.

5. Frequently Asked Questions (FAQ)

Q1: Does this include post-translational modifications?
A: No, this calculates the theoretical molecular weight of the unmodified polypeptide chain.

Q2: How accurate is this calculation?
A: It's accurate for the amino acid sequence, but actual measured MW may differ due to protein folding, modifications, or buffer effects.

Q3: What about N-terminal and C-terminal groups?
A: The calculation assumes standard protonated N-terminal and deprotonated C-terminal groups at neutral pH.

Q4: Can I use three-letter amino acid codes?
A: No, only single-letter codes are accepted in this calculator.

Q5: What about selenocysteine or pyrrolysine?
A: These non-standard amino acids are not included in this calculator's database.