Final answer:
Cell membranes contain integral proteins that span the bilayer, peripheral proteins that attach to the membrane surface, and lipid-anchored proteins that are covalently bound to lipids within the membrane. Each type differs in how they interact with the membrane and their respective roles in cellular functions.
Step-by-step explanation:
In the structure of cellular membranes, there are several types of membrane proteins that play crucial roles: integral proteins, peripheral proteins, and lipid-anchored proteins.
Integral proteins are embedded within the phospholipid bilayer of the membrane. They may span the entire membrane, with portions that are hydrophobic and interact with the lipid core, and hydrophilic regions that extend into the aqueous environments on either side of the membrane. These proteins can function as channels or pumps to move substances across the membrane.
Peripheral proteins are not embedded in the lipid bilayer. Instead, they are loosely attached to the outer or inner surfaces of the membrane, often through interactions with integral proteins or the polar heads of lipids. These proteins may act as enzymes or be involved in the structural stability of the cell.
Lastly, lipid-anchored proteins are covalently attached to lipids within the membrane, anchoring them to one side of the bilayer, while not spanning the entire membrane. These proteins can also participate in cellular signaling and function as receptors.