Final answer:
Porin proteins are integral membrane proteins that form pores within cellular membranes, allowing selective passage of ions and small polar molecules and contributing importantly to cell function and communication.
Step-by-step explanation:
Porin proteins play a critical structural role in cellular membranes by forming pores that span across the membrane. These proteins are integral and provide a pathway for the passage of ions and small polar molecules, which are otherwise impeded by the hydrophobic lipid bilayer. Porins contribute to membrane functionality by facilitating the selective permeability of the membrane, allowing for the exchange of substances essential for cell survival and function. They can also have enzymatic functions and play a part in cell recognition through interactions with glycoproteins and glycolipids on the membrane's exterior.
Peripheral membrane proteins, while not penetrating the membrane, still influence membrane functionality by mediating connections between the membrane and cytoskeletal elements, which affect cell shape and mobility. Additionally, they can regulate the activities of transmembrane protein complexes, and contribute to cellular adhesion and communication. Porin proteins, being integral membrane proteins, include hydrophilic domains for pore formation, anchored by hydrophobic domains within the membrane, accommodating the movement of substances that are otherwise incompatible with the lipid bilayer.