Membranes with more saturated fatty acids are more ridgid
Lipid bilayers are impermeable to ions and most polar molecules, helping create an ion or concentration gradient
Many proteins use alpha-helices to cross the membrane since there is a hydrophobic region in the middle
Prostaglandin H2 synthase has a hydrophobic channel that moves substrates into the active site. Blockage of this hydrophobic channel inhibits prostaglandin H2 synthase, leading decreased inflammation
Potassium ion channel selectivity filter...
the diameter of the channel opening from the inside of the cell is smaller than the opening to the exterior, creating a selectivity filter that allows only K+ to pass.
K+ ion interaction with K+ channel protein
The diameter of the channel gets smaller and smaller until the K+ are forced to lose their shell of water and interact with the oxygens of the protein
Why can't sodium ions pass through the K+ channel if they're smaller?
Na+ ions are too small to interact favourably with the selectivity filter. The free-energy costs of dehydrating ions is considerable, and the channel pays the cost of dehydration K+ ions by providing interactions with the carbonyl oxygen atoms. The costs of dehydrating Na+ cannot be recovered, so Na+ stays hydrated
