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Protein Molecular Weight Formula:
Where:
MW (g/mol) - Protein molecular weight
MWaa (g/mol) - Molecular weight per amino acid
length (aa) - Number of amino acids in sequence
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The molecular weight of a protein is the sum of the masses of all its atoms. In practice, it's calculated by adding the molecular weights of all amino acids in the sequence and subtracting the weight of water molecules lost during peptide bond formation (18 g/mol per bond).
The calculator uses the formula:
Where:
Explanation: Each peptide bond formation results in the loss of one water molecule, hence we subtract 18 g/mol for each bond formed (which is length-1 for a protein).
Details: Knowing a protein's molecular weight is essential for laboratory work including gel electrophoresis, mass spectrometry, protein purification, and biochemical assays.
Tips: Enter the protein sequence using single-letter amino acid codes (A-Z). The calculator automatically ignores non-letter characters and converts letters to uppercase.
Q1: Does this include post-translational modifications?
A: No, this calculator only considers the amino acid sequence. PTMs like phosphorylation or glycosylation would add additional mass.
Q2: How accurate is this calculation?
A: It provides the theoretical average molecular weight based on standard amino acid masses. Actual mass may vary slightly due to isotopic distributions.
Q3: What about N-terminal or C-terminal modifications?
A: This calculator assumes standard amino and carboxyl termini. Special modifications would need to be accounted for separately.
Q4: Can I use lowercase letters?
A: Yes, the calculator automatically converts to uppercase, but only standard amino acid letters (A-Z) are processed.
Q5: What's the maximum sequence length?
A: There's no strict limit, but extremely long sequences may take longer to process.