ProteinQuest
A tiny game about the alphabet of life. Proteins are built from just 20 amino acids, and each one has a side chain with a personality: some hide from water, some love it, some carry a charge. Sort each residue into its property class and learn the 20 letters as you play. Nothing is installed; nothing about you is collected.
This is the tool — a free learning game with no login, no score-keeping account, no ads, and nothing tracked. The 20 amino acids and their classes are shown in full in the guide below, which works with or without JavaScript. A native version, when it ships, adds Files and offline use; it never gates the web.
Loading the game… If it does not start, the full amino-acid guide below still works.
How to play. Press Start. A residue appears with its one-letter and three-letter codes. Decide which property class its side chain belongs to and choose it — tap the bin on the board, click a class button, or press keys 1–5. You will sort all 20 amino acids across 12 rounds. There is no timer and no way to lose: if you pick a different class, the tile shows you where it really goes.
The five property classes
- Hydrophobic. Water-avoiding side chains. They tuck into the oily core of a folded protein, away from water.
- Polar. Water-friendly but uncharged side chains. They often sit on the protein surface and make hydrogen bonds.
- Positive. Basic side chains that carry a positive charge near cell pH. They attract negatively-charged partners.
- Negative. Acidic side chains that carry a negative charge near cell pH. They attract positively-charged partners.
- Special. Glycine has only a hydrogen for a side chain — the smallest, most flexible residue of all.
The 20 standard amino acids
Every protein in your body is a chain built from these twenty building blocks. Each is shown with its three-letter code (used in structure files) and its one-letter code (used in sequences), plus the property class its side chain belongs to in this game.
| Amino acid | Three-letter | One-letter | Class |
|---|---|---|---|
| Alanine | ALA | A | Hydrophobic |
| Valine | VAL | V | Hydrophobic |
| Leucine | LEU | L | Hydrophobic |
| Isoleucine | ILE | I | Hydrophobic |
| Proline | PRO | P | Hydrophobic |
| Phenylalanine | PHE | F | Hydrophobic |
| Methionine | MET | M | Hydrophobic |
| Tryptophan | TRP | W | Hydrophobic |
| Serine | SER | S | Polar |
| Threonine | THR | T | Polar |
| Asparagine | ASN | N | Polar |
| Glutamine | GLN | Q | Polar |
| Tyrosine | TYR | Y | Polar |
| Cysteine | CYS | C | Polar |
| Lysine | LYS | K | Positive |
| Arginine | ARG | R | Positive |
| Histidine | HIS | H | Positive |
| Aspartate | ASP | D | Negative |
| Glutamate | GLU | E | Negative |
| Glycine | GLY | G | Special |
Methods & about
This is a teaching model, and it is honest about being a simplification. Real side-chain chemistry is a spectrum, and textbooks draw the class boundaries slightly differently. This edition uses a common five-bucket scheme: Cysteine and Tyrosine are grouped as polar (they carry polar –SH / –OH groups); Histidine is grouped as positive (a basic side chain, partly charged near cell pH); Glycine is special — its whole side chain is a single hydrogen, so it is the smallest and most flexible residue and does not sit cleanly in the other classes. Proline is treated as hydrophobic here. The codes (for example Tryptophan = W / TRP, Lysine = K / LYS, Aspartate = D / ASP) are the standard IUPAC ones. The game keeps no score history, uses no accounts, and sends nothing anywhere.
Want the deeper, native experience — reading-tier text, a peptide-chain builder, and on-device explanations? See the Fold Commons apps. Everything we make is free and non-profit; learn more on the home page.