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Molecular Weight Calculation:
Where \(n_i\) is the count and \(m_i\) is the molecular weight of each residue
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Protein molecular weight calculation determines the mass of a protein based on its amino acid sequence. This is essential for various biochemical applications including protein purification, electrophoresis, and mass spectrometry analysis.
The calculator uses the formula:
Where:
Explanation: The calculation sums the molecular weights of all amino acids in the sequence plus the molecular weight of water (for the terminal groups).
Details: Accurate molecular weight estimation is crucial for protein identification, quantification, experimental design, and interpreting analytical results in proteomics research.
Tips: Enter the protein sequence using single-letter amino acid codes. The sequence should contain only valid amino acid characters (A-Z, excluding B, J, X, Z which have ambiguous meanings).
Q1: What are daltons (Da)?
A: Daltons are the standard unit for molecular mass, where 1 Da is defined as 1/12 of the mass of a carbon-12 atom.
Q2: Does this calculator account for post-translational modifications?
A: No, this calculator provides the theoretical molecular weight of the unmodified polypeptide chain. Modifications like phosphorylation or glycosylation will increase the actual molecular weight.
Q3: Why is water molecular weight added?
A: Water (H₂O) is added because during protein synthesis, a water molecule is lost for each peptide bond formed, but the terminal amino and carboxyl groups remain intact.
Q4: What about disulfide bonds?
A: Disulfide bonds between cysteine residues are not accounted for in this calculation as they don't change the atomic composition (just the connectivity).
Q5: How accurate is this calculation?
A: This provides the theoretical average molecular weight. For precise work, consider isotopic distribution and use monoisotopic mass if needed.