Why proteins fold the way they do

A protein is a chain of amino acids, and it always folds into the same shape. It's tempting to picture the chain "finding" its bonds like a key finding a lock — but the real driver is simpler and stranger: water. Some amino acids are hydrophobic (they disrupt water's structure), so water pushes them together into a buried core, away from itself, to stay as disordered as possible. The fold isn't chosen by the protein. It's forced by water's entropy.

AlphaFold predicted 3D structure of human STK3, a ribbon diagram colored by prediction confidence
A real fold: predicted structure of human STK3 (UniProt Q13188), from the AlphaFold Protein Structure Database — the same image blurred behind the header above. One chain, one shape: water forced this exact fold, the same way it'll force whatever chain you build below.

Fold the simplified chain below yourself, one step at a time, and watch the score change as hydrophobic residues get buried or left exposed.

Dragging picks a fresh random chain of that length.

Your fold

Energy: 0 (residue 1 of 14 placed)

Use the arrow keys or WASD, or click the buttons above. Backspace undoes a step.

Read more about the HP model behind this toy →