1. What is Molecular Weight Calculation?

The molecular weight (MW) of a protein or peptide is the sum of the masses of its constituent amino acids plus one water molecule (for the terminal groups). This calculator provides the monoisotopic molecular weight based on the amino acid sequence.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( AA\_masses \) — Masses of individual amino acids (g/mol)
• 18.01528 — Mass of water (H₂O) added for terminal groups

Explanation: The calculator sums the masses of each amino acid in the sequence and adds the mass of one water molecule to account for the N-terminal hydrogen and C-terminal hydroxyl groups.

3. Importance of Molecular Weight

Details: Knowing the molecular weight is essential for protein quantification, electrophoresis, mass spectrometry, and many biochemical experiments. It helps in determining protein concentration and in experimental design.

4. Using the Calculator

Tips: Enter the amino acid sequence using single-letter codes (e.g., "GAMMA"). The sequence is case-insensitive and spaces are automatically removed. Only standard 20 amino acids are supported.

5. Frequently Asked Questions (FAQ)

Q1: What are the single-letter codes for amino acids?
A: A (Alanine), R (Arginine), N (Asparagine), D (Aspartic acid), C (Cysteine), E (Glutamic acid), Q (Glutamine), G (Glycine), H (Histidine), I (Isoleucine), L (Leucine), K (Lysine), M (Methionine), F (Phenylalanine), P (Proline), S (Serine), T (Threonine), W (Tryptophan), Y (Tyrosine), V (Valine).

Q2: Does this include post-translational modifications?
A: No, this calculator only considers the unmodified amino acid sequence. For modified proteins, you would need to add the mass of the modifications manually.

Q3: Why is water added to the calculation?
A: The water accounts for the extra hydrogen at the N-terminus and hydroxyl group at the C-terminus in a complete peptide chain.

Q4: What's the difference between monoisotopic and average mass?
A: Monoisotopic mass uses the most abundant isotope for each element, while average mass accounts for natural isotope abundance. This calculator uses monoisotopic masses.

Q5: Can I calculate the mass of a peptide with non-standard amino acids?
A: This calculator only supports standard amino acids. For non-standard residues, you would need specialized software that includes their masses.