Science & Lab Tools
Protein Molecular Weight Calculator
Calculate the molecular weight of proteins by entering their amino acid sequence or composition.
Enter a protein sequence or composition to see results
Related to Protein Molecular Weight Calculator
The Protein Molecular Weight Calculator determines the molecular mass of proteins by summing the individual masses of amino acids in the sequence and accounting for water loss during peptide bond formation. The calculator accepts either a complete amino acid sequence using single-letter codes or a composition listing the number of each amino acid type.
Calculation Method
The calculator follows these steps: 1. Identifies each amino acid in the sequence or composition 2. Multiplies each amino acid by its molecular weight 3. Sums the total molecular weight 4. Subtracts water weight lost in peptide bond formation (18.015 g/mol per bond) 5. Provides the final molecular weight in g/mol
Amino Acid Weights
Standard amino acid molecular weights (g/mol): Alanine (A): 89.1, Arginine (R): 174.2, Asparagine (N): 132.1, Aspartic acid (D): 133.1, Cysteine (C): 121.2, Glutamic acid (E): 147.1, Glutamine (Q): 146.2, Glycine (G): 75.1, Histidine (H): 155.2, Isoleucine (I): 131.2, Leucine (L): 131.2, Lysine (K): 146.2, Methionine (M): 149.2, Phenylalanine (F): 165.2, Proline (P): 115.1, Serine (S): 105.1, Threonine (T): 119.1, Tryptophan (W): 204.2, Tyrosine (Y): 181.2, Valine (V): 117.1
The calculator provides three key pieces of information: the total molecular weight of the protein, the number of amino acids, and the amino acid composition. Understanding these results is crucial for various biochemical applications.
Molecular Weight
The molecular weight is given in grams per mole (g/mol). This value represents the mass of one mole of your protein and is essential for: • Calculating molar concentrations • Preparing protein solutions • Analyzing protein gel electrophoresis results • Planning protein purification strategies
Amino Acid Composition
The composition breakdown shows the frequency of each amino acid in your protein. This information is valuable for: • Analyzing protein properties • Predicting protein behavior • Planning protein synthesis • Estimating protein stability
1. Why is molecular weight important for proteins?
Molecular weight is a fundamental property of proteins that is essential for many biochemical applications. It helps determine protein concentrations, calculate stoichiometry in reactions, prepare solutions for experiments, and analyze protein separation techniques like gel electrophoresis or size exclusion chromatography.
2. Why is water weight subtracted in the calculation?
During protein synthesis, amino acids join together through peptide bonds, and each bond formation releases one water molecule (H₂O, 18.015 g/mol). For a protein with n amino acids, there are (n-1) peptide bonds, so we subtract (n-1) × 18.015 g/mol from the sum of individual amino acid weights to get the correct final protein mass.
3. How accurate is this molecular weight calculation?
The calculator provides the theoretical molecular weight based on the standard masses of amino acids and peptide bond formation. While highly accurate for the primary structure, it doesn't account for post-translational modifications, disulfide bonds, or other chemical modifications that might affect the actual mass of the protein in biological systems.
4. What are the accepted input formats?
The calculator accepts two input formats: 1) A protein sequence using standard single-letter amino acid codes (e.g., MKWVTFISLLLLFSSAYS), or 2) An amino acid composition listing the number of each amino acid (e.g., A:5, K:3, M:1). Both formats will yield the same result if they represent the same protein composition.
5. What is the scientific source for this calculator?
This calculator uses the standardized molecular weights of amino acids as established by the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Biochemistry and Molecular Biology (IUBMB). The calculation methodology follows fundamental principles of protein chemistry described in standard biochemistry textbooks such as Lehninger Principles of Biochemistry and Stryer Biochemistry. The water loss in peptide bond formation (18.015 g/mol) is based on the well-established chemistry of peptide bond formation, documented in numerous scientific publications and biochemistry reference materials.