Why colour by property
A raw sequence is a wall of letters, and the eye cannot pick out that positions 4 through 9 are all hydrophobic. Colouring by side chain property makes clusters visible immediately: a block of one colour is a region of one character.
That is what most sequence questions come down to. Where are the charges, are they spread out or clustered, is there a hydrophobic stretch, where are the cysteines that might pair.
What patterns to look for
Alternating charge and hydrophobicity with a period of three or four residues suggests an amphipathic helix, one face polar and the other not. Those peptides are surface-active and tend to aggregate at interfaces.
A contiguous block of hydrophobic residues suggests a region that will drive aggregation or need a co-solvent. A cluster of like charges suggests a region whose ionisation will be shifted by its own neighbours, which is exactly where the independent-groups charge model is least accurate.
- •Contiguous hydrophobic block: aggregation and solubility risk.
- •Alternating polar and nonpolar with period 3 to 4: possible amphipathic helix.
- •Two or more cysteines: possible disulfide bridges, wanted or unwanted.
- •Asn or Gln followed by Gly: a deamidation motif.
- •Methionine or tryptophan: oxidation-prone positions.
Numbering and orientation
Sequences are written and numbered from the N-terminus to the C-terminus, left to right, which is the direction of biosynthesis and the universal convention in the literature. Position one is the N-terminal residue.
Getting this backwards flips every position reference in a paper or a certificate. When a disulfide is described as 1-6, it means the first and sixth residues counting from the N-terminus.
How the visualisation is built
A per-residue property lookup mapped to a colour, laid out in numbered blocks so any position can be located by counting rather than by scanning.
position(i) = i + 1, counting from the N-terminus colour(i) = colour assigned to the property group of residue i block marks = every 10 residues
- Parse to standard residues. Non-standard characters are stripped so that numbering counts residues, not keystrokes. A pasted FASTA header does not shift every position by its own length.
- Assign a property group. Each residue maps to exactly one group, so the colouring is a partition rather than an overlay.
- Colour consistently with the other tools. The same group colours are used across the composition, structure and visualisation tools, so a reader moving between them does not have to relearn the key.
- Mark every tenth position. Decade markers make counting to an arbitrary position quick, which is what you need when checking a position reference from a certificate or a paper.
What this method cannot tell you
- •Property groups are a conventional simplification. Glycine, proline and tyrosine each sit awkwardly in any small set of categories.
- •It shows the primary sequence only. Secondary and tertiary structure are not represented and cannot be inferred from the colouring.
- •Non-standard residues, D-amino acids and modifications cannot be shown, because they cannot be entered.
- •A visual pattern is a prompt to check something, not evidence in itself.
Sequence visualizer: frequently asked questions
Each colour marks a side chain property group: nonpolar, polar, aromatic, positively charged and negatively charged.
The same colour scheme is used across the composition, structure and visualisation tools so the key does not change as you move between them.
From the N-terminus to the C-terminus, left to right. Position one is the N-terminal residue.
This is the direction of biosynthesis and the universal convention. Reading it backwards inverts every position reference in a paper or a certificate.
The end of the chain with a free amino group, which is the start of the sequence as conventionally written.
It is often modified in synthetic peptides, most commonly by acetylation, which removes its positive charge and adds 42.01 daltons.
The end with a free carboxyl group, at the right-hand end of the written sequence.
Amidation is the common modification here. It removes the negative charge and makes the peptide 0.98 daltons lighter than the free acid form.
A few recur often enough to be worth checking every time:
- •A contiguous block of nonpolar residues, which signals aggregation and solubility risk
- •Regular alternation of polar and nonpolar with a period of three or four, which suggests an amphipathic helix
- •Two or more cysteines, which can form bridges
- •Asn or Gln followed by Gly, a deamidation motif
Yes. The header line and line breaks are stripped along with any other non-residue characters before numbering begins, so position one is the first real residue.
Because they turn locating position 37 from a scan into a count of three markers plus seven. Position references in certificates and papers are given as numbers, and finding them by eye in an unmarked string is slow and error-prone.
No. It shows the primary sequence coloured by residue property. Helices, sheets and turns are not represented and cannot be read off from the colouring.
The structure renderer draws a schematic backbone, which is closer to a structural view but still a schematic rather than a prediction.
Single-letter code has no way to express stereochemistry. D and L forms of the same residue share a code.
The convention in the literature is a lowercase letter or a d- prefix in three-letter code, neither of which this input accepts.
The positive and negative groups mark residues that carry charge at neutral pH. Histidine is grouped as positive although it is only slightly ionised at pH 7.4.
For the actual fractional charge at a given pH, the charge at pH calculator computes it group by group.
Glycine has no side chain at all, only a hydrogen, so it fits no group cleanly. It is grouped with the small and polar residues here by convention.
Its real significance is structural: it is the most flexible residue and often marks a turn.
Yes, though at protein length the coloured string becomes a texture rather than something you read residue by residue.
For long sequences the hydrophobicity plotter is usually the more informative view, because it summarises regions rather than positions.
It removes anything that is not one of the twenty standard codes. It cannot tell you whether the remaining sequence is the peptide you meant to enter.
Cross-checking the residue count and the molecular weight against the certificate is the practical validation.
Proline's ring locks the backbone and cannot donate a backbone hydrogen bond, so it breaks helices and sheets and frequently marks a turn.
A proline-rich sequence such as BPC-157 has a distinctive conformational character that its composition alone does not convey.
There is no export function. Selecting and copying the text copies the residues without the colouring, since the colour lives in the page styling rather than in the characters.
No. Everything runs in your browser, nothing is transmitted, and the sequence is discarded when you close the page.
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