What are the two types of proteins that associate the plasma membrane?

The two main types of proteins that associate the plasma membrane are integral proteins and peripheral proteins. 

Integral Proteins

Integral proteins have at least one hydrophobic region and are embedded permanently within the lipid bilayer, extending across the membrane. The hydrophobic region anchors the integral proteins to the hydrophobic core of the phospholipid bilayer. 

Some integral proteins stretch from one side of the entire membrane to the other while others are only partially embedded. Integral proteins that span the entire membrane are called transmembrane proteins. They may cross the membrane just once (single-pass membrane proteins) or they may cross the membrane several times (multi-pass membrane proteins).  

Integral proteins serve several functions as transporters, receptors, enzymes, or structural elements. Transmembrane proteins are especially crucial for facilitating the movement of molecules across the membrane and for sensing the extracellular environment.

Peripheral Proteins

Peripheral proteins are found on the inner or outer membrane surface but are not embedded in the lipid bilayer. They may adhere loosely and temporarily to integral proteins or interact with the polar head groups of phospholipids.

Peripheral proteins serve diverse functions, including participating in cell signaling, providing structural support, and supporting membrane shape and flexibility. An important characteristic of peripheral proteins is their ability to associate and dissociate from the membrane based on cellular needs.