Other Specific Interactions Mediated by Membrane Proteins

Other Specific Interactions Mediated by Membrane Proteins 

A variety of signals can be transmitted across membranes without the actual flow of a substance from one side of the membrane to the other. We saw in chapter 12 that some hormones bind to specific receptor sites on the outer surface of the plasma membrane, thereby triggering metabolic changes on the cytosolic side of the membrane. Hormonal systems that function in this way are discussed in greater detail in chapter 24. Other membrane proteins mediate specific cell-cell interactions. Sometimes these interactions merely stimulate particular types of cells to bind to one another, but often they also trigger reactions that result in proliferation or differentiation of the interacting cells. We discuss signals of this type when we consider the interaction between the B and T cells of the immune system (see Supplement 3). 

In this chapter we discussed the structure and function of biological membranes. First we considered their structure starting with an examination of the constituents of membranes. Then we turned to questions concerning the transport of materials across membranes. 

Biological membranes consist primarily of proteins and lipids whose relative amounts vary considerably. 

There are two main types of lipids in biological membranes Phospholipids and sterols. The predominant phospholipids in most membranes are phosphoglycerides, which are phosphate esters 

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