Protein Molecular Weight Calculator

Protein Molecular Weight Formula:

\[ MW = \sum AA_{MW} - (n-1) \times 18 \]

Molecular Weight:

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1. What Is Protein Molecular Weight?

Protein molecular weight is the sum of the atomic weights of all atoms in a protein molecule. For proteins, it's calculated by summing the molecular weights of individual amino acids and subtracting the weight of 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 acid residues
18 — Molecular weight of water (g/mol)

Explanation: The equation accounts for water molecules lost during the formation of peptide bonds 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 amino acid sequence using single-letter codes (e.g., "GAMMA"). The sequence should contain only valid amino acid codes (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 (n-1)×18 in the formula?
A: Each peptide bond formation results in the loss of one water molecule (MW = 18 g/mol). For a protein with n amino acids, there are (n-1) peptide bonds.

Q2: Does this calculation include post-translational modifications?
A: No, this calculator provides the theoretical molecular weight of the unmodified polypeptide chain. Post-translational modifications would add additional mass.

Q3: What about N-terminal and C-terminal modifications?
A: This calculation assumes standard amino and carboxyl termini. Modified termini (e.g., acetylated N-terminus) would affect the molecular weight.

Q4: How accurate is this calculation?
A: This provides a theoretical molecular weight based on average atomic masses. For precise measurements, experimental techniques like mass spectrometry are needed.

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.