Types of Compounds. Ionic compounds are compounds composed of ions, charged particles that form when an atom (or group of atoms, in the case of polyatomic ions) gains or loses electrons. 1  A cation is a positively charged ion. 2  An anion is a negatively charged ion.
Porins are members of an extended family of transmembrane proteins found in the outer membrane of gram negative bacteria such as E. coli, or in the outer membranes of mitochondria in eukaryotes. The general porins provide a simple diffusion pathway across the membrane for molecules less than 1 kDa with little substrate selectivity.
The next broad category of proteins we will consider are the carrier molecules or transport proteins. These transport proteins are often globular proteins. They are generally tightly packed with polar side groups on the outside to enhance their solubility in water. They typically have nonpolar side groups folded to the inside to keep water from getting in and unfolding them. Serum albumin is one example.