Proteins hormone-binding, 259 immune

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). 

Insulin and human growth hormone, discussed above, are classic protein hormones produced with recombinant DNA technology. The immune system produces protein antibodies that attack disease causing-agents such bacteria and viruses. Genetic antibody production interferes with or attacks entities associated with diseases such as psoriatic arthritis and Crohn s disease. Recombinant DNA technology produces proteins binding with specialized white blood cells to reduce inflammation associated with rheumatoid arthritis. 

There is no life without cells and there are no cells without membranes. The cell membrane of animal cells is very important in that it protects the organelles and also keeps undesired particles from entering the cell body. Proteins span the membrane and touch both the inside and outside of the cell. Their function is to interact with molecules outside the cell which includes the ability to serve as protein receptors for hormones, to bind to other cells in wound healing and in the immune response, and to transport molecules into and out of the cell. What is outlined in these few sentences, however, is a very complex biological system which has been described only phenomenologically for a long time. 

A variety of symptoms, not mentioned earlier, have also been associated with zinc deficiency. Zinc deficiency is thought to delay woxmd healing, impair the senses of taste and smell, and impair the functions of the immune system. (The impaired sense of taste is called hypogettsia.) Severe zinc deficiency results in impairment of the immune system and increased infections. These problems have been found in the severe deficiencies that occur in starvation (marasmus) and acrodermatitis enteropathica and in studies with animals. The immune system involves a large array of hormones, hormone receptor proteins, signaling proteins, and DNA-binding proteins, some of which require zinc for activity. It is not clear which of these components is most sensitive to zinc deficiency. 

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