So porin is an integral protein, more specifically, a transmembrane integral protein, because it spans the entire membrane. It's found in bacterial cells, for instance, equalized cells. It acts as a channel, a pore, a whole, allowing certain molecules, polar molecules, to actually pass across. Now, it consists predominantly of beta pleated sheets that run in an antiparallel direction, as shown here. So one error goes here, the other error goes here. And it consists of alternating hydrophobic and hydrophilic amino acids.