Final answer:
A sesquiterpene consists of three isoprene units and has a total of 15 carbons in its structure.
Step-by-step explanation:
A sesquiterpene is a type of terpene that is made up of three isoprene units, which are five-carbon building blocks. This means that a sesquiterpene has a total of 15 carbons in its molecular structure.
The five-carbon skeleton of isoprene units is a common structural motif in many natural compounds, and prenols, for example, are synthesized using five-carbon isoprene precursors like isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP).
By joining these isoprene units, compounds such as monoterpene (10 carbons), sesquiterpene (15 carbons), diterpene (20 carbons), and others are formed, each varying in the number of isoprene units and hence the number of carbons.