Fatty Acid Chain Elongation (The Four Steps)

Summary

In this episode of "Wonders of Chemistry," Mickey Gee explores the four key steps of chain elongation in the production of palmitic acid, a C16 fatty acid. He reviews the role of enzymes, coenzymes like NADPH, and the commitment step involving acetyl-CoA. The process entails a series of reactions—condensation, hydrogenation, dehydration, and a final hydrogenation—each requiring energy inputs like ATP. By the end, viewers gain insight into the complexity of lipogenesis, including the total resources required for the production of palmitic acid. Upcoming episodes will delve into hormonal regulation of this metabolic process.

Takeaways

• 😀 Chain elongation is the process of adding two-carbon units to create the C16 fatty acid known as palmitic acid.
• 🔍 A total of seven chain elongation steps are required to produce palmitic acid from acetyl CoA.
• 🍽️ Acetyl CoA, derived from food intake, serves as the primary input for the chain elongation process.
• 💡 Insulin plays a crucial role in activating the commitment step for lipogenesis by promoting the enzyme acetyl-CoA carboxylase.
• 🔗 The multi-enzyme complex fatty acid synthase is responsible for the actual chain elongation and fatty acid synthesis.
• 📋 Preparatory steps are necessary to attach both a three-carbon malonyl group and a two-carbon acetyl unit to fatty acid synthase.
• ⚛️ Each chain elongation involves four distinct steps: condensation reaction, hydrogenation, dehydration, and a second hydrogenation.
• ⚡ Energy inputs for each chain elongation include one ATP and two NADPH, with a total requirement of seven ATPs and 14 NADPHs for palmitic acid production.
• 🔄 The process requires eight acetyl CoA molecules in total, as each C16 fatty acid consists of eight two-carbon units.
• 🔔 Future episodes will cover hormonal regulation of lipogenesis and its effects on associated metabolic pathways.

Q & A

What is palmitic acid?

Palmitic acid is a C16 fatty acid that is produced through the process of chain elongation during lipogenesis.

How many chain elongations are required to produce palmitic acid?

A total of seven chain elongations are required to produce palmitic acid.

What role does insulin play in chain elongation?

Insulin activates the commitment step in lipogenesis, which includes the expression of the enzyme acetyl-CoA carboxylase that produces malonyl-CoA.

What are the four steps involved in each chain elongation?

The four steps are: 1) condensation reaction, 2) hydrogenation reaction, 3) dehydration reaction, and 4) a second hydrogenation reaction.

What is the significance of NADPH in the chain elongation process?

NADPH is crucial as it provides reducing power for the reduction reactions during steps two and four of chain elongation.

Why is ATP necessary for chain elongation?

ATP is necessary as it provides the energy required to form the high-energy thioester bond during the condensation reaction.

What happens to the carbon dioxide during the chain elongation process?

During the first step of chain elongation, a carbon is eliminated in the form of carbon dioxide, contributing to the formation of a longer fatty acid chain.

How does the pentose phosphate pathway relate to NADPH?

The pentose phosphate pathway is responsible for regenerating NADPH in the cytosol, which is necessary for continued lipogenesis.

What is the role of malonyl-CoA in chain elongation?

Malonyl-CoA serves as the source of two-carbon units that are added to the growing fatty acid chain during each chain elongation cycle.

Why do we need more NADPH than acetyl-CoA during the chain elongation process?

Each chain elongation cycle requires two NADPH (for steps two and four), resulting in a total of 14 NADPH needed for the seven cycles, whereas only eight acetyl-CoA are required.