© Flickr, Creative Commons License. Author: AJC1, 18 April 2007.
Prions, familiar from their role in mad cow disease, can take on two rather different conformations. The prion on the right, in a helical conformation, dissolves easily in water and is relatively benign. The prion on the left, in a beta-sheet conformation, tends to stick to other similar prions and forms plaques. These plaques disrupt the structure of healthy tissue, resulting in the "spongy" texture found in the brains of infected animals. (Unit: 9)