Question

Natural rubber is a polymer of

• A. Isopentenyl units
• B. Amino acids
• C. Glucose units
• D. Steroid glycosides

Hint:

All terpenes and rubber are polymers of 5-carbon isoprene building blocks. Isopentenyl pyrophosphate (IPP) is the active 5-carbon precursor, making "isopentenyl units" the correct biochemical answer for rubber polymer units.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Plants produce a wide array of secondary metabolites classified into terpenes, phenolics, and nitrogen-containing compounds.
Terpenes (or isoprenoids) are synthesized from five-carbon building blocks and represent the largest class of plant secondary products.

Step 2: Detailed Explanation:
Natural rubber, harvested as latex from the rubber tree (Hevea brasiliensis), is a high-molecular-weight terpene.
Biochemically, it is a polymer composed of thousands of five-carbon isoprene units (specifically, cis-1,4-polyisoprene).
These five-carbon units are derived from the active precursor isopentenyl pyrophosphate (IPP) (isopentenyl units), which is synthesized via either the mevalonate (MVA) pathway in the cytosol or the methylerythritol phosphate (MEP) pathway in plastids.
In rubber biosynthesis, the sequential addition of these isopentenyl units is catalyzed by the enzyme rubber transferase on the surface of latex rubber particles.
Let us review other options:
- Amino acids (B) are the building blocks of proteins.
- Glucose units (C) are the building blocks of polysaccharides like cellulose and starch.
- Steroid glycosides (D) are complex glycosylated triterpenes (like saponins or cardenolides).

Step 3: Final Answer:
Natural rubber is a polymer of isopentenyl units, which corresponds to option (A).