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4. The ABCs of Drug Action in the Brain > The Brain—A Survival Organ

The Brain—A Survival Organ

The overall process of neurotransmission works very well and, of course, it should. It has been honed and perfected over eons of evolution. We know that the brain is an organ critical for our survival. The more poorly working versions of the brain (and we assume there were some) were presumably lost because they couldn’t compete with “smarter” brains during evolution. When we think of how many different processes are critical for survival, and how the brain mediates and coordinates them, it is truly amazing—even humbling.


Neurotransmitter Synthesis and Storage

The way that neurotransmitters are synthesized depends on which neurotransmitter you are considering. Small molecule neurotransmitters such as dopamine, which is critical for the addiction process (discussed later), are made from amino acid precursors through the actions of enzymes. An enzyme is nothing more than a protein that makes new molecules by facilitating molecular changes. The changes that are made can result in building structures by adding atoms or joining smaller molecules together. Conversely the changes can be a breakdown of molecules by removing atoms or by splitting off parts of molecules. Several enzymes often act in a sequence to produce neurotransmitter molecules, which are unique structures. The substances produced and altered along the way are referred to as intermediates. For example, dopamine is made from a widely occurring amino acid, tyrosine. An OH (hydroxyl, oxygen, and hydrogen bound together) group is added to the tyrosine by the enzyme tyrosine hydroxylase to produce the intermediate dihydroxyphenylalanine (DOPA). Then that intermediate is acted upon by the enzyme DOPA decarboxylase to produce dopamine. Because each neurotransmitter has a unique structure, it is synthesized by its own unique set of enzymes and processes. The enzymes and process....


  

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