Protein Molecular Weight Calculator From Sequence

Protein Molecular Weight Formula:

\[ MW = \sum AA\ MW - (n-1) \times 18 \]

Molecular Weight:

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1. What is Protein Molecular Weight Calculation?

Protein molecular weight calculation determines 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 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:

\( MW \) — Molecular weight (g/mol)
\( \sum AA\ MW \) — Sum of amino acid molecular weights
\( n \) — Number of amino acids in the sequence
\( 18 \) — Molecular weight of water (g/mol)

Explanation: The equation accounts for the condensation reaction where water is removed during peptide bond formation between amino acids.

3. Importance of Molecular Weight Calculation

Details: Knowing a protein's molecular weight is essential for various applications including protein purification, gel electrophoresis, mass spectrometry, and biochemical research.

4. Using the Calculator

Tips: Enter the protein sequence using single-letter amino acid codes (A, R, N, D, C, E, Q, G, H, I, L, K, M, F, P, S, T, W, Y, V). The sequence can be entered in any case as it will be converted to uppercase automatically.

5. Frequently Asked Questions (FAQ)

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

Q2: Does this calculation account for post-translational modifications?
A: No, this calculator provides the theoretical molecular weight of the unmodified polypeptide chain. Modifications like phosphorylation or glycosylation would add additional mass.

Q3: What about disulfide bonds?
A: Disulfide bond formation involves loss of hydrogen atoms (2g/mol per bond), which is not accounted for in this basic calculation.

Q4: Are terminal groups considered?
A: This calculation assumes standard neutral terminal groups (-NH₂ and -COOH). For precise calculations with specific terminal modifications, additional adjustments would be needed.

Q5: How accurate is this calculation?
A: This provides a theoretical average molecular weight. Actual measured values may vary slightly due to isotopic distributions and other factors.