Amino Acid Composition
Analyze the amino acid composition of a protein sequence.
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What it does
The amino acid composition tool breaks a protein sequence into the count, percentage and mass contribution of each of the 20 standard amino acids. It helps characterize unknown proteins, compare sequences, and estimate molecular weight.
How it works
The tool scans the sequence residue by residue, tallies how many times each amino acid appears, computes its percentage of the total length, and multiplies by the residue mass to give its mass contribution. Summing all residue mass contributions and adding water (18.015 Da) yields the molecular weight. Composition also reveals physicochemical bias, such as high hydrophobic or high charged content.
Worked example
For the sequence MKNFTGALA, the analysis shows Met 1 (10 percent), Lys 1, Asn 1, Phe 1, Thr 1, Gly 1, Ala 2 (20 percent), for a total of 9 residues, with each mass contribution summed to the overall molecular weight.
When to use it
Estimate whether a protein is rich in certain residues that affect purification, such as cysteine for disulfide bonds. Compare compositional bias between homologs from different organisms. Quickly estimate molecular weight and residue totals from a pasted sequence.
FAQ
- What does amino acid composition tell you about a protein?
- It reports how many of each residue are present, their percentage of the sequence, and their mass contribution, revealing biases in charge, hydrophobicity and cysteine content.
- How is the percentage of an amino acid calculated?
- Divide the count of that residue by the total number of residues in the sequence and multiply by 100.
- Can composition analysis estimate molecular weight?
- Yes, summing each residue's mass contribution across all 20 types and adding one water molecule (18.015 Da) gives the molecular weight.
- Why does composition matter for purification?
- High cysteine suggests disulfide bonds, high hydrophobic content affects solubilizing detergents, and charged residues guide ion-exchange choices, so composition guides method selection.