Terpenes are made up of two or more five-carbon groups known as isoprenes. The triterpenoid lanosterol, a steroid precursor, is shown below. How many isoprene units are present in lanosterol?

Question

Terpenes are made up of two or more five-carbon groups known as isoprenes.  The triterpenoid lanosterol, a steroid precursor, is shown below.  How many isoprene units are present in lanosterol?

Quizplus · Accepted Answer

11ecba2d_127d_51c5_a3bf_1f96cfc5d1ad_MD0008_00 Terpenes are lipid precursors to steroids and lipid signaling molecules, and are generally isolated from plants. These compounds are made up of branched five-carbon groups, called isoprene units, in which the branched end is referred to as the head and the unbranched end is the tail. Isoprene units can be joined to form terpenes in one of three ways: Head-to-tail, tail-to-tail, or head-to-head. Terpenes are categorized according to how many isoprenes are present. For example, the most basic terpene is made up of two isoprene units (10 carbon atoms total) and is known as a monoterpene. A diterpene contains double the number of isoprene units and carbon atoms as a monoterpene, giving a diterpene four isoprene units and 20 carbon atoms. Molecules made of isoprene units that also contain nonhydrocarbon functional groups are called terpenoids. Lanosterol is a triterpenoid, which can be thought of as three monoterpenes together. Therefore, it is composed of six isoprene units (3 terpenes × 2 isoprenes/terpene = 6 isoprenes) and has 30 carbon atoms in total because 6 isoprenes × 5 carbons/isoprene = 30 carbon atoms. (Choice A) A triterpene can be thought of as three monoterpenes put together, which would contain six isoprenes rather than three. A terpene with three isoprenes is known as a sesquiterpene (1.5 monoterpenes). (Choices B and D) Terpenes with four and eight isoprenes are known as diterpenes and tetraterpenes, respectively. Educational objective: Terpenes are a type of lipid made up of branched five-carbon units known as isoprenes. Terpenes are classified according to the number of isoprene units in the molecule.

Terpenes Are Made Up of Two or More Five-Carbon Groups