Protein Molecular Weight And Pi Calculator

Protein Molecular Weight and Isoelectric Point Calculation:

\[ MW = \sum AA \text{ (amino acid weights)} \] \[ pI = \text{Average of pKa values} \]

Molecular Weight:

Isoelectric Point (pI):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is Protein Molecular Weight and pI?

Protein molecular weight is the sum of the atomic weights of all atoms in a protein molecule, typically measured in daltons (Da). The isoelectric point (pI) is the pH at which a protein carries no net electrical charge.

2. How Does the Calculator Work?

The calculator uses the following formulas:

\[ MW = \sum \text{(amino acid weights)} + 18.02 \text{ (for water molecule)} \] \[ pI = \text{Average pKa values of ionizable groups} \]

Where:

MW - Molecular weight in daltons
pI - Isoelectric point in pH units
Amino acid weights - Standard molecular weights for each amino acid residue
pKa values - Acid dissociation constants for ionizable groups

3. Importance of MW and pI Calculation

Details: Knowing a protein's molecular weight and isoelectric point is essential for protein purification, electrophoresis, chromatography, and understanding protein structure-function relationships.

4. Using the Calculator

Tips: Enter the amino acid sequence using single-letter codes (e.g., "MALWMRLLPLL"). The calculator will ignore invalid characters and calculate based on standard amino acids.

5. Frequently Asked Questions (FAQ)

Q1: What are the standard amino acid codes?
A: Standard single-letter codes: A, R, N, D, C, E, Q, G, H, I, L, K, M, F, P, S, T, W, Y, V.

Q2: Why is water (18.02 Da) added to the calculation?
A: Water is added because protein synthesis involves condensation reactions that release water molecules for each peptide bond formed.

Q3: How accurate is the pI calculation?
A: This provides an approximation. Actual pI depends on protein structure, modifications, and environmental factors.

Q4: Can I use three-letter amino acid codes?
A: No, this calculator only accepts single-letter codes for amino acids.

Q5: What about modified amino acids?
A: This calculator uses standard amino acid weights and doesn't account for post-translational modifications.