What is the difference between biochemical, pharmaceutical, and diagnostic chemical reactions?
We are talking about biochemical, pharmaceutical, and diagnostic chemical reactions. Biochemical reactions are chemical reactions that naturally take place in living organisms like plants and animals. They usually involve large organic chemicals (biochemicals) like lipids, proteins, nucleic acids, etc. Pharmaceutical chemical reactions involve the chemistry that takes place when a medicine is introduced into the body to evoke a certain pharmacological or physiological effect. In many cases this involves a small molecule having a very specific reaction with a protein or polysaccharide to do things like inhibiting an enzyme or activate a cell signalling system. Finally, a diagnostic chemical reaction is one that involves a diagnostic chemical test to measure or test a certain aspect of a person's health. A sample of a person's body chemistry is obtained (urine sample, blood sample, etc.) and treated with a particular chemical or set of chemicals as part of a test to aid in a diagnosis by a healthcare professional.
So while all of these reactions are health related, biochemistry is what naturally takes place within an organism, pharmaceutical chemistry is what happens in the organism upon the introduction of a specific medicine, and diagnostic chemistry usually takes place in a testing instrument or vessel outside of the organism.