Introduction:

 Terpenoids, also known as isoprenoids, are a diverse and vast class of natural compounds that play crucial roles in various biological processes and have numerous applications in industries such as pharmaceuticals, cosmetics, and agriculture. These compounds are derived from the basic building blocks called isoprene units (C5H8), and they exhibit an incredible range of structural diversity, functions, and properties.

Pathways :

Biosynthetic pathways of terpenoids involve a series of enzymatic reactions that assemble isoprene units to create complex terpene structures. These pathways are classified into two major types: the mevalonate (MVA) pathway and the methylerythritol phosphate (MEP) pathway, also known as the deoxyxylulose phosphate (DOXP) pathway. The choice of pathway depends on the organism, with some organisms using the MVA pathway, while others rely on the MEP pathway.

1. Mevalonate (MVA) Pathway:

 This pathway is primarily found in eukaryotic organisms, including animals and fungi.

 It starts with the condensation of two molecules of acetyl-CoA, forming acetoacetyl-CoA, which is then converted into 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA).

 HMG-CoA is further converted into mevalonate through a series of enzymatic reactions.

 Mevalonate is then phosphorylated and undergoes subsequent transformations to produce isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP), the fundamental isoprene units. 

These isoprene units are then used as building blocks for the synthesis of various terpenoids.

2. Methylerythritol Phosphate (MEP) Pathway:

  This pathway is primarily found in prokaryotes, including bacteria and plants' chloroplasts.

  It starts with the condensation of glyceraldehyde-3-phosphate and pyruvate to form 1-deoxy-D-xylulose-5-phosphate (DOXP).

  DOXP undergoes a series of enzymatic reactions to produce IPP and DMAPP.

  These IPP and DMAPP molecules serve as the precursors for terpenoid biosynthesis.


After the formation of IPP and DMAPP, terpenoid biosynthesis diverges into various branches, leading to the

synthesis of different classes of terpenoids, including monoterpenes, sesquiterpenes, diterpenes, triterpenes, and tetraterpenes. These compounds play essential roles in nature, such as serving as components of essential oils in plants, contributing to the scent and flavor of various fruits and flowers, and acting as chemical defenses against herbivores.

Additionally, terpenoids have significant applications in various industries. For example, they are used in the pharmaceutical industry as the basis for the production of drugs like taxol (a diterpene used in cancer treatment) and artemisinin (a sesquiterpene used to treat malaria). Terpenoids are also widely employed in the cosmetics industry for their aromatic properties and skin benefits.

In summary, the biosynthetic pathways of terpenoids, whether through the mevalonate or methylerythritol phosphate pathways, are intricate and involve the assembly of isoprene units into a wide array of natural compounds with diverse functions and applications. These compounds continue to be a subject of scientific research and innovation due to their biological significance and industrial potential.