Calculate Protein Weight From Sequence

Protein Molecular Weight Formula:

\[ MW = \sum(MW_{aa}) - 18 \times (length - 1) \]

Where:
MW (g/mol) - Molecular weight of protein
MW_aa (g/mol) - Molecular weight of amino acid
length (aa) - Number of amino acids in sequence

Protein Molecular Weight:

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is Protein Molecular Weight?

Protein molecular weight is the sum of the masses of all atoms in a protein molecule. It's typically expressed in Daltons (Da) or grams per mole (g/mol). The weight is calculated from the amino acid sequence, accounting for water loss during peptide bond formation.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ MW = \sum(MW_{aa}) - 18 \times (length - 1) \]

Where:

\( MW \) — Molecular weight of protein (g/mol)
\( MW_{aa} \) — Molecular weight of individual amino acids (g/mol)
\( length \) — Number of amino acids in the sequence
18 — Molecular weight of water (g/mol)

Explanation: The equation sums the weights of all amino acids, then subtracts the weight of water molecules lost during peptide bond formation (one per bond).

3. Importance of Protein Weight Calculation

Details: Knowing a protein's molecular weight is essential for SDS-PAGE, mass spectrometry, protein purification, concentration determination, and biochemical experiments.

4. Using the Calculator

Tips: Enter the protein sequence using single-letter amino acid codes (A-Z). The sequence should only contain standard amino acid characters (ACDEFGHIKLMNPQRSTVWY).

5. Frequently Asked Questions (FAQ)

Q1: Does this include post-translational modifications?
A: No, this calculates the theoretical weight of the unmodified polypeptide chain. PTMs would add additional mass.

Q2: How accurate is this calculation?
A: It's theoretically accurate for the amino acid sequence, but actual measured weight may differ due to factors like isotopic distribution.

Q3: What about N-terminal methionine cleavage?
A: This calculator assumes the sequence exactly as entered. Remove the initiating methionine if your protein undergoes this modification.

Q4: Does it account for disulfide bonds?
A: No, disulfide bonds form between cysteines but don't change the molecular weight (just subtract 2 hydrogens per bond).

Q5: What's the difference between average and monoisotopic mass?
A: This calculator provides average mass, which considers natural isotopic abundance. Monoisotopic mass uses only the most abundant isotopes.