Protein Molecular Weight Calculator Peptide 1

Protein Molecular Weight Formula:

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

Molecular Weight:

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1. What is Protein Molecular Weight?

The molecular weight (MW) of a protein or peptide is the sum of the masses of its amino acids minus the mass of water molecules lost during peptide bond formation. It's a fundamental property used in protein analysis, purification, and characterization.

2. How Does the Calculator Work?

The calculator uses the formula:

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

Where:

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

Explanation: For each peptide bond formed, one water molecule is lost (condensation reaction). Therefore, for a protein with n amino acids, (n-1) water molecules are lost.

3. Importance of Molecular Weight Calculation

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

4. Using the Calculator

Tips: Enter the amino acid sequence in single-letter (e.g., GAS) or three-letter code (e.g., GLY-ALA-SER). The calculator automatically recognizes both formats.

5. Frequently Asked Questions (FAQ)

Q1: Does this include post-translational modifications?
A: No, this calculator provides the theoretical molecular weight of the unmodified peptide chain only.

Q2: How accurate is this calculation?
A: It's accurate for theoretical calculations, but actual measured MW may differ due to factors like hydration and protein folding.

Q3: What about N-terminal and C-terminal modifications?
A: This calculator assumes standard NH2- and COOH- termini. For modified termini, you would need to adjust the calculation manually.

Q4: Can I calculate MW for non-standard amino acids?
A: This calculator only includes the 20 standard amino acids. Non-standard residues would require manual calculation.

Q5: Why subtract water molecules?
A: Water is lost during peptide bond formation (condensation reaction), so it must be accounted for in the total molecular weight.