Fatty Acid Synthesis - Part II

Summary

This video delves into the process of fatty acid synthesis, explaining the steps involved in the formation of palmitic acid, the primary product in our body. The script covers the importance of acetyl-CoA as the monomer and ATP as the energy source for this anabolic reaction. Key enzymes, like acetyl-CoA carboxylase and fatty acid synthase, drive the process forward, with NADPH providing the reducing power. The regulation of fatty acid synthesis is also discussed, including hormonal control and allosteric activators like citrate, as well as inhibitors like long-chain fatty acids and glucagon.

Takeaways

• 😀 Fatty acid synthesis is an anabolic process where monomers (acetyl-CoA) are linked together to form a polymer (fatty acid chain).
• 😀 Anabolic reactions, like fatty acid synthesis, generally require an input of energy because they have a positive delta G value, meaning they are not spontaneous.
• 😀 ATP is used to fuel fatty acid synthesis by coupling with reactions that have a favorable delta G value, ensuring the process occurs.
• 😀 The primary product of fatty acid synthesis in humans is palmitic acid, a 16-carbon fatty acid chain, formed from eight acetyl-CoA molecules.
• 😀 The synthesis of palmitic acid requires 7 ATP molecules, 14 NADPH molecules, and results in the production of ADP, NADP+, phosphate groups, and water.
• 😀 Acetyl-CoA is converted to malonyl-CoA in a thermodynamically unfavorable reaction, which is driven forward by the hydrolysis of ATP.
• 😀 Malonyl-CoA is the activated form of acetyl-CoA, which is used in the polymerization process to form fatty acids.
• 😀 The polymerization step involves the loss of carbon dioxide from malonyl-CoA and the use of NADPH to reduce carbon-carbon double bonds into saturated bonds.
• 😀 The enzyme acetyl-CoA carboxylase regulates the first step of fatty acid synthesis and is subject to allosteric regulation and hormonal control (e.g., insulin activates, long-chain fatty acids and glucagon inhibit).
• 😀 The polymerization of fatty acids is catalyzed by fatty acid synthase, which links malonyl-CoA subunits to form the growing fatty acid chain.
• 😀 After synthesis, palmitic acid can be used to create longer-chain fatty acids and is eventually incorporated into triglycerides for storage or transport via VLDL to tissues.

Q & A

What is the general theme of anabolic reactions in the body?

Anabolic reactions involve linking monomers together to form polymers. These reactions require an input of energy as they are generally not spontaneous, indicated by a positive delta G.

Why are anabolic reactions, like fatty acid synthesis, not spontaneous?

Anabolic reactions have a positive delta G, meaning they require energy input to occur. This is because the formation of polymers from monomers is thermodynamically unfavorable without an energy source.

How does the body overcome the energy challenge in anabolic reactions like fatty acid synthesis?

The body couples anabolic reactions with reactions that have a negative delta G, such as ATP hydrolysis. The energy released from ATP hydrolysis drives the anabolic process forward.

What is the role of ATP in fatty acid synthesis?

ATP provides the necessary energy to activate acetyl-CoA to malonyl-CoA and drive the overall fatty acid synthesis reaction by coupling with reactions that have favorable delta G values.

What is the monomer used in fatty acid synthesis, and how is it polymerized?

The monomer in fatty acid synthesis is acetyl-CoA, a two-carbon molecule. It is polymerized by linking multiple acetyl-CoA molecules together in a process that elongates the fatty acid chain, typically resulting in palmitic acid (a 16-carbon chain).

What are the main reactants involved in fatty acid synthesis, and what is their fate?

The main reactants in fatty acid synthesis are acetyl-CoA, ATP, and NADPH. Acetyl-CoA is used to build the fatty acid chain, ATP is hydrolyzed to drive the reactions, and NADPH is used to reduce carbon-carbon bonds during polymerization.

How is malonyl-CoA formed and what is its significance in fatty acid synthesis?

Malonyl-CoA is formed by adding a carbon dioxide molecule to acetyl-CoA through the enzyme acetyl-CoA carboxylase. This activation step is critical because malonyl-CoA is the building block that will be added to the growing fatty acid chain.

What is the role of NADPH in fatty acid synthesis?

NADPH provides the reducing power needed to reduce the carbon-carbon double bonds during fatty acid synthesis, enabling the formation of saturated carbon chains by adding hydrogen atoms.

What is the function of acetyl-CoA carboxylase in fatty acid synthesis?

Acetyl-CoA carboxylase is responsible for converting acetyl-CoA into malonyl-CoA. It is a rate-limiting enzyme in the fatty acid synthesis pathway, meaning it controls the speed of the entire process.

How is the activity of acetyl-CoA carboxylase regulated?

Acetyl-CoA carboxylase is regulated through allosteric modulation and hormonal control. Citrate activates it, while long-chain fatty acids inhibit it. Hormones like insulin stimulate it, while glucagon inhibits it, reflecting the body's metabolic state.

What are the key steps in the polymerization process of fatty acid synthesis?

The polymerization process involves the attachment of malonyl-CoA to the fatty acid synthase enzyme, where the carbon dioxide is removed, and the growing fatty acid chain is elongated by adding two-carbon units. NADPH is used for reduction, and water is lost as a byproduct.

What is the final product of fatty acid synthesis, and how is it used in the body?

The final product of fatty acid synthesis is palmitic acid, a 16-carbon saturated fatty acid. This fatty acid can be further modified to create longer-chain fatty acids or can be used to form triacylglycerols for energy storage and transport.