Calculate Protein Molecular Weight From Amino Acid Sequence

Protein Molecular Weight Formula:

\[ MW = \sum AA_{MW} - (n-1) \times 18 \]

Protein Molecular Weight (MW):

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1. What is Protein Molecular Weight Calculation?

Protein molecular weight calculation estimates the mass of a protein based on its amino acid sequence. The calculation accounts for the molecular weights of individual amino acids and subtracts the mass of water molecules lost during peptide bond formation.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ MW = \sum AA_{MW} - (n-1) \times 18 \]

Where:

\( MW \) — Protein molecular weight (g/mol)
\( \sum AA_{MW} \) — Sum of amino acid molecular weights (g/mol)
\( n \) — Number of amino acids in the sequence
18 — Molecular weight of water (g/mol) lost per peptide bond

Explanation: The equation accounts for the dehydration synthesis that occurs during protein formation, where each peptide bond results in the loss of one water molecule.

3. Importance of Protein Molecular Weight

Details: Knowing a protein's molecular weight is crucial for protein purification, electrophoresis, mass spectrometry analysis, and various biochemical applications where precise molecular size matters.

4. Using the Calculator

Tips: Enter the amino acid sequence using single-letter codes (A, R, N, D, C, Q, E, G, H, I, L, K, M, F, P, S, T, W, Y, V). The calculator will automatically ignore any non-amino acid characters.

5. Frequently Asked Questions (FAQ)

Q1: Why subtract (n-1)×18 from the sum?
A: This accounts for the water molecules lost during the formation of (n-1) peptide bonds in the protein chain.

Q2: Does this include post-translational modifications?
A: No, this calculation provides the theoretical molecular weight of the unmodified polypeptide chain only.

Q3: How accurate is this calculation?
A: It provides a theoretical value accurate for most purposes, but actual experimental values may vary due to protein folding and other factors.

Q4: What about N-terminal and C-terminal modifications?
A: This calculation assumes standard amino and carboxyl termini. Special modifications are not accounted for.

Q5: Can I use three-letter codes?
A: No, the calculator only accepts single-letter amino acid codes. Three-letter codes will be filtered out.