Protein Calculator Molecular Weight

Protein Molecular Weight Formula:

\[ MW = \sum (AA_{MW} - 18) \]

Molecular Weight:

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1. What is Protein Molecular Weight Calculation?

Protein molecular weight calculation estimates the mass of a protein based on its amino acid sequence. The calculation accounts for the molecular weight of each amino acid minus the water molecule lost during peptide bond formation.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ MW = \sum (AA_{MW} - 18) \]

Where:

\( MW \) — Molecular weight (g/mol)
\( AA_{MW} \) — Molecular weight of individual amino acid (g/mol)
18 — Molecular weight of water (g/mol) subtracted for each peptide bond

Explanation: The formula sums the molecular weights of all amino acids in the sequence, subtracting 18 g/mol (the molecular weight of water) for each peptide bond formed between amino acids.

3. Importance of Protein Molecular Weight

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

4. Using the Calculator

Tips: Enter the protein sequence using single-letter amino acid codes (e.g., "MALWMRLLPLL"). The sequence should contain only standard amino acid characters (A, R, N, D, C, E, Q, G, H, I, L, K, M, F, P, S, T, W, Y, V).

5. Frequently Asked Questions (FAQ)

Q1: Why subtract 18 for each amino acid?
A: During peptide bond formation, a water molecule (MW = 18 g/mol) is removed for each bond created between 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 the N-terminal and C-terminal groups?
A: The calculation assumes standard protonation states at physiological pH, with an NH₃⁺ group at the N-terminus and a COO⁻ group at the C-terminus.

Q4: How accurate is this calculation?
A: This provides a theoretical molecular weight that is typically within 1% of the actual mass for most proteins, excluding modifications.

Q5: Can I use three-letter amino acid codes?
A: No, this calculator only accepts single-letter amino acid codes without spaces or other characters.