Two input modes
Use Build a peptide to click amino acid buttons one by one β each key is colour-coded by category (acidic, basic, polar, nonpolar) and labeled with the standard one-letter and three-letter codes. Use Paste sequence to drop in any raw sequence string β for example from UniProt, PDB, or any FASTA file. Non-standard characters are automatically ignored.
Molecular Weight
Calculated as the sum of the residue weights of all amino acids, minus one water molecule per peptide bond (18.02 Da). The result is the molecular weight of the full peptide chain, not free amino acids in solution.
Isoelectric Point (pI)
The pI is the pH at which the net charge of the peptide is zero. It is calculated iteratively using the standard Henderson-Hasselbalch equation applied to the ionisable groups: the N-terminus (pKa 8.0), C-terminus (pKa 3.1), and the side chains of Asp, Glu, His, Cys, Tyr, Lys, and Arg.
Hydrophobicity Plot
Uses the Kyte-Doolittle scale β the most widely used hydrophobicity scale in biochemistry, published in 1982. Each amino acid is assigned a score from +4.5 (most hydrophobic, Isoleucine) to β4.5 (most hydrophilic, Arginine). The plot shows a sliding window average across the sequence, helping identify transmembrane segments and buried hydrophobic cores.
Composition Chart
Shows the count and percentage of each amino acid present in the sequence, sorted by frequency. Bars are colour-coded by category. Useful for identifying unusually amino acid-rich sequences β for example, collagen is roughly one-third glycine.
Category Breakdown
The donut chart shows the proportion of acidic, basic, polar, and nonpolar amino acids β giving a quick visual sense of the overall chemical character of the sequence.