Schematic drawing of the 3D structure of the photosynthetic reaction center<a class="external autonumber" href="https://en.wikipedia.org/wiki/Photosynthetic_reaction_centre">[1]</a> from Rhodopseudomonas viridis.  The membrane is shown as pale yellow, bacteriochlorophylls are green, hemes in the cytochrome are red, and transmembrane alpha-helices are gold cylinders.  This was the first crystal structure of a membrane protein, earning a Nobel Prize in 1988.  Coordinates from <span class="plainlinks"><a href="https://en.wikipedia.org/wiki/Protein_Data_Bank" class="extiw" title="w:Protein Data Bank">PDB</a>: <a rel="nofollow" class="external text" href="http://www.rcsb.org/pdb/explore/explore.do?structureId=1PRC">1PRC</a></span>​; drawn by Jane Richardson, scanned and touched up by David Richardson.
<a href="//commons.wikimedia.org/wiki/User:Dcrjsr" title="User:Dcrjsr">Dcrjsr</a>
CC BY 3.0
<span class="int-own-work" lang="en">Own work</span>