Isoprenoids

Isoprenoids, also known as terpenoids, are a large and diverse class of naturally occurring organic chemicals derived from five-carbon isoprene units assembled and modified in thousands of ways. They are a major class of plant secondary metabolites and have various roles in plant physiology, including defense against herbivores and pathogens, and attracting pollinators. In addition to their ecological functions, isoprenoids have significant applications in medicine, perfumery, and food industries.

Structure and Biosynthesis

Isoprenoids are built from isoprene units, which have the molecular formula C5H8. These units are linked together to form a wide variety of structures. The basic molecular formula of isoprenoids is (C5H8)_n, where n is the number of linked isoprene units. This can vary from a simple monoterpenoid (two isoprene units) to complex polymers like natural rubber (thousands of isoprene units).

The biosynthesis of isoprenoids occurs via two distinct pathways:

• The Mevalonate pathway: This pathway occurs in the cytosol of eukaryotic cells and starts with acetyl-CoA. It is primarily responsible for the synthesis of sterols, including cholesterol in animals and phytosterols in plants.
• The Methylerythritol phosphate (MEP) pathway: This pathway occurs in the plastids of plants and some microorganisms. It uses pyruvate and glyceraldehyde 3-phosphate as substrates.

Both pathways lead to the production of the five-carbon building blocks isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), which are the precursors to all isoprenoids.

Functions and Uses

Isoprenoids play a crucial role in various biological functions:

• In plants, they are involved in growth regulation, photosynthesis (e.g., carotenoids), and protection against environmental stresses.
• They serve as precursors to vitamins and hormones. For example, vitamin A is derived from the isoprenoid beta-carotene.
• Isoprenoids like limonene and pinene are major components of essential oils and are used in fragrances and flavorings.

In medicine, isoprenoids have therapeutic properties. For instance:

• Taxol (paclitaxel), a complex diterpene, is used in cancer therapy.
• Artemisinin, a sesquiterpene lactone derived from the plant Artemisia annua, is effective against malaria.

Economic and Industrial Significance

Isoprenoids have substantial economic importance. They are key ingredients in perfumes, cosmetics, food additives, and pharmaceuticals. The versatility in their structure allows for a wide range of applications, making them valuable in various industries.

Environmental Impact

Isoprenoids also have an environmental impact. For example, isoprene emitted by trees is a major precursor to natural tropospheric ozone, playing a significant role in the chemistry of the atmosphere.

Conclusion

Isoprenoids are not only fundamental to plant life but also have extensive applications in human industries and medicine. Their wide range of functions and uses makes them a significant area of study in both the biological and applied sciences.