Calculate Protein Molecular Weight From Amino Acid Sequence

Molecular Weight Formula:

\[ MW (Da) = \sum (AA\ residue\ MW (Da)) + 18 \]

Molecular Weight:

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1. What is Protein Molecular Weight Calculation?

Protein molecular weight calculation determines the mass of a protein molecule by summing the molecular weights of its constituent amino acid residues plus the weight of one water molecule (18 Da) that is lost during peptide bond formation.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ MW (Da) = \sum (AA\ residue\ MW (Da)) + 18 \]

Where:

\( \sum (AA\ residue\ MW (Da)) \) — Sum of molecular weights of all amino acid residues
\( + 18 \) — Molecular weight of water added for complete protein

Explanation: The calculation accounts for the loss of water molecules during peptide bond formation and provides the complete molecular weight of the protein.

3. Importance of Molecular Weight Calculation

Details: Accurate molecular weight determination is crucial for protein characterization, experimental design, gel electrophoresis, mass spectrometry, and various biochemical applications.

4. Using the Calculator

Tips: Enter the protein sequence using single-letter amino acid codes (A, R, N, D, C, E, Q, G, H, I, L, K, M, F, P, S, T, W, Y, V). The sequence should not contain spaces or invalid characters.

5. Frequently Asked Questions (FAQ)

Q1: Why add 18 Da to the sum of residues?
A: The +18 Da accounts for the water molecule that is added when the protein is fully hydrated, representing the complete molecular weight.

Q2: What are the valid amino acid codes?
A: Valid single-letter codes: A, R, N, D, C, E, Q, G, H, I, L, K, M, F, P, S, T, W, Y, V (case insensitive).

Q3: Does this include post-translational modifications?
A: No, this calculation provides the theoretical molecular weight based only on the amino acid sequence without modifications.

Q4: How accurate is this calculation?
A: This provides the theoretical average molecular weight. Actual experimental values may vary due to isotopic distribution and other factors.

Q5: Can I calculate molecular weight for modified amino acids?
A: This calculator uses standard amino acid weights. For modified residues, manual calculation or specialized tools are needed.