Some Physiological pH Effects

Life processes are largely ionic and molecular interactions in aqueous media. Most of the materials involved are pH sensitive and may change their state of protonation as pH shifts. Polymers like the nucleic acids (RNA and DNA) and the proteins (especially enzymes) may change drastically in configuration and ability to function as pH is changed. 

Phosphates are minor buffering agents in blood but major ones within the cells. The important role of the polyphosphates and their sugar derivatives, especially with adenosine, is described later in this chapter. Their acidities are related to phosphoric acids. 

Another important system is NH4-NH3 with pKl 9.24. These are one product of protein catabolism. The acid ion, NH4, can pass through the kidney tubules to be excreted, another means of removing acid from the body. The urine pH varies from about 5 to 7.5 according to the momentary need for elimination of acid in the form of NH4 and also H2PO4. This method, slower than respiration, depends upon recent diet and activity. Citric, lactic, and pyruvic acids and their derivatives are also metabolically important. 

The pH controls the precipitation of CaC03 in the oceans and the formation of the shells of crustaceans. The blood of animals is nearly saturated with respect to CaHP04 and apatite, Cas0H(P04)3, the major mineral of bone. A slight increase in pH in certain cells can shift the H2PO4 of blood to more HPO and PO to cause deposition of bone. 

These few examples are a sample of the vast number occurring in the study of life processes. Several of these precipitations are treated in detail in Chapter 11. 

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