Mevalonic pathway

Summary

The Mevalonic acid pathway is essential for producing terpene hydrocarbons, which are vital secondary metabolites in plants. The pathway begins with the combination of two acetyl-CoA molecules to form acetoacetyl-CoA, which is further processed into mevalonic acid through several enzymatic reactions. This 6-carbon compound undergoes phosphorylation and decarboxylation, yielding isopentyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP). These serve as foundational units for synthesizing larger terpenes, including geranyl, farnesyl, and geranylgeranyl pyrophosphates. The pathway highlights the complex biochemical interactions involved in producing essential plant metabolites.

Takeaways

• 🧪 The Mevalonic acid pathway is crucial for producing terpene hydrocarbons, which serve as secondary metabolites in plants.
• 🔗 The pathway begins with the condensation of 2 acetyl-CoA molecules catalyzed by acyl-CoA-acetyltransferase to form acetoacetyl-CoA.
• 🔄 Acetoacetyl-CoA reacts with another acetyl-CoA to produce beta-hydroxy-beta-methyl-glutaryl-CoA (HMG-CoA) through the enzyme HMG-CoA synthase.
• ⚡ HMG-CoA is reduced by beta-hydroxy-beta-methyl-glutaryl-CoA reductase using NADPH to form mevalonic acid, a non-linear 6-carbon compound.
• 💡 Mevalonic acid undergoes phosphorylation with ATP to yield mevalonic acid-5-pyrophosphate, which is a key building block in terpene synthesis.
• 🌱 The mevalonic acid-5-pyrophosphate is converted to isopentyl pyrophosphate (IPP) through a reaction with ATP and the enzyme diphosphomevalonate decarboxylase.
• 📏 Isopentyl pyrophosphate (IPP) can isomerize to dimethylallyl pyrophosphate (DMAPP), both serving as fundamental units for terpene formation.
• 🔗 One molecule each of IPP and DMAPP combine to form geranyl pyrophosphate (GPP), a 10-carbon compound.
• 🌳 Further reactions of GPP with IPP yield farnesyl pyrophosphate (FPP) with 15 carbons, and additional reactions can create larger terpene molecules.
• 🌿 Terpenes are essential secondary metabolites in plants, with complex structures arising from the combination of basic isoprenoid units.

Q & A

What is the primary function of the Mevalonic acid pathway?

The Mevalonic acid pathway is primarily used for the production of terpene hydrocarbons, which are important secondary metabolites in plants.

What initiates the Mevalonic acid pathway?

The pathway begins with two acetyl-CoA molecules that combine using the enzyme acyl-CoA-acetyltransferase to form acetoacetyl-CoA.

How is mevalonic acid formed in the pathway?

Mevalonic acid is formed from beta-hydroxy-beta-methyl-glutaryl-CoA through a reaction with 2 NADPH and 2 protons, catalyzed by the enzyme beta-hydroxy-beta-methyl-glutaryl-CoA reductase.

What is the significance of pyrophosphate in the Mevalonic acid pathway?

Pyrophosphate indicates the presence of two adjacent phosphorus atoms, and it plays a role in the conversion of mevalonic acid into mevalonic acid-5-pyrophosphate, a key intermediate for terpene synthesis.

What are isoprene units and their role in the pathway?

Isoprene units, such as isopentyl pyrophosphate (IPP), are five-carbon compounds that serve as the foundational building blocks for more complex hydrocarbons in the synthesis of terpenes.

How do IPP and DMAPP contribute to the formation of terpenes?

One molecule of IPP combines with one molecule of dimethylallyl pyrophosphate (DMAPP) to form geranyl pyrophosphate, which can further react to produce larger terpenes.

What is the structure of geranyl pyrophosphate?

Geranyl pyrophosphate contains 10 carbon atoms and is formed from the combination of IPP and DMAPP, releasing a pyrophosphate molecule in the process.

What larger molecules can be formed in the pathway?

Larger molecules such as farnesyl pyrophosphate (15 carbons) and geranylgeranyl pyrophosphate (20 carbons) can be formed through the sequential addition of IPP to geranyl pyrophosphate and farnesyl pyrophosphate.

Why are terpenes considered important in plants?

Terpenes are essential secondary metabolites that play various roles in plant biology, including growth regulation, defense against herbivores, and attracting pollinators.

What enzymes are crucial for the reactions in the Mevalonic acid pathway?

Key enzymes in the pathway include acyl-CoA-acetyltransferase, beta-hydroxy-beta-methyl-glutaryl-CoA reductase, and diphosphomevalonate decarboxylase.