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In chemistry, a precursor is a compound that participates in a chemical reaction that produces another compound. In biochemistry , the term "precursor" often refers more specifically to a chemical compound preceding another in a metabolic pathway , such as a protein precursor .
Drug precursors, also referred to as precursor chemicals or simply precursors, are substances used to manufacture illicit drugs. Most precursors also have legitimate commercial uses and are legally used in a wide variety of industrial processes and consumer products, such as medicines, flavourings, and fragrances.
Precursor (physics), a phenomenon of wave propagation in dispersive media; Precursor in the course of a disease, a state preceding a particular stage in that course; Precursor cell (biology), a unipotent stem cell; Earthquake precursor, a diagnostic phenomenon that can occur before an earthquake; Gehrlein Precursor, a glider
l-DOPA is the precursor to the neurotransmitters dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline), which are collectively known as catecholamines. Furthermore, l -DOPA itself mediates neurotrophic factor release by the brain and CNS.
Thus the direct precursor of norepinephrine is dopamine, which is synthesized indirectly from the essential amino acid phenylalanine or the non-essential amino acid tyrosine. [12] These amino acids are found in nearly every protein and, as such, are provided by ingestion of protein-containing food, with tyrosine being the most common.
Squalene is a biochemical precursor to both steroids and hopanoids. [12] For sterols, the squalene conversion begins with oxidation (via squalene monooxygenase) of one of its terminal double bonds, resulting in 2,3-oxidosqualene.
Tyrosine is a precursor to neurotransmitters and increases plasma neurotransmitter levels (particularly dopamine and norepinephrine), [29] but has little if any effect on mood in normal subjects. [30] [31] [32]
These precursors react with the surface of a material one at a time in a sequential, self-limiting, manner. A thin film is slowly deposited through repeated exposure to separate precursors. ALD is a key process in fabricating semiconductor devices , and part of the set of tools for synthesizing nanomaterials .