Isoprenoid

Isoprenoids are natural compounds assembled from five-carbon building blocks derived from isoprene. Their structures range from small volatile molecules to large polymers and membrane components.

Isoprene: A five-carbon hydrocarbon, 2-methyl-1,3-butadiene, that gives its name to isoprenoid building blocks. Its carbon skeleton supplies the family’s defining five-carbon pattern.
Mevalonate pathway: A metabolic pathway that produces isopentenyl pyrophosphate through mevalonate. It supplies isoprenoid precursors in animals, fungi, and many other organisms.
Cholesterol: A sterol that forms part of animal cell membranes and serves as a precursor to steroid hormones and bile acids. This major animal isoprenoid illustrates both membrane and biosynthetic roles.
Isoprene rule: A structural heuristic that relates terpene skeletons to assemblies of five-carbon units. It captures the family’s characteristic pattern while not describing every structure literally.
Isopentenyl pyrophosphate: An activated five-carbon intermediate used by organisms to build isoprenoids. It is one of the two universal activated units assembled into isoprenoid chains.
Methylerythritol phosphate pathway: A metabolic pathway that produces isoprenoid precursors from pyruvate and glyceraldehyde 3-phosphate. It provides an alternative route to the same activated five-carbon building blocks.
Carotenoid: A family of pigmented isoprenoids that includes light-harvesting and photoprotective molecules. Their conjugated structures give plants and microbes color while helping manage light.
Endosymbiotic theory: The theory that mitochondria and plastids originated from bacteria living inside ancestral cells. Plastid ancestry helps explain why plants use a distinct precursor-producing pathway.
Dimethylallyl pyrophosphate: An activated five-carbon isomer of isopentenyl pyrophosphate that initiates many isoprenoid chains. It commonly starts chain assembly by combining with isopentenyl pyrophosphate.
Prenyltransferase: An enzyme that joins isoprenoid units to form longer prenyl diphosphates. These enzymes determine chain length and provide substrates for later synthesis.

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