Two proteins: On the left, the iron storage protein ferritin, composed of 24 polypeptide L- (FTL) and H- (FTH) polypeptide subunit. FTH, within the ferritin protein, catalyzes the ferrous (Fe2+) – ferric (Fe3+) reaction (image from M Stowell, UC Boulder). Underneath and to the right, a negative-stain electron micrograph image of membranes, isolated from the electric ray Torpedo californicus, packed with acetylcholine receptor (AChR) proteins (arrow points to one protein). The AChR is composed of four distinct polypeptides (α,β,ɣ,?) in a 2:1;1;1 ratio that acts as a gated ion channel (source: M.W. Klymkowsky).
bioliteracy / biofundamentals 