Pharmacodynamics: How drugs elicit a physiological effect

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Chapter 19 Pharmacodynamics

How drugs elicit a physiological effect

Proteins play an integral role in controlling body functions through their roles as:

The chemical composition of protein molecules allows for great variation in three-dimensional structure, creating sites which, generally speaking, will interact only with specific molecules that are able to fit into the particular site (see Figure 11.5, p. 84). Most drugs act by interfering with this process at the molecular level, fitting into sites intended for the original protein molecule.

Enzymes

The enzyme reaction site is fairly specific (see Figure 11.5, p. 84), which is why metabolic pathways are associated with specific enzymes.

Enzyme Inhibition

Most enzyme receptor sites are not completely specific (there is some structural leeway given the number of combinations possible and the mobility of the protein) and a relatively similarly shaped molecule might be able to achieve a ‘close fit’. This creates competition for molecules of a similar shape and the original molecule might find itself unable to find a binding site because it is already occupied. Many drugs are designed to take advantage of this phenomenon.

The various ways in which enzyme function can be affected are not dissimilar to the ways receptor function can be affected. These principles are worth bearing in mind when looking at chemicals that act directly on receptor sites.

• Irreversible Inhibition

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