Fatty Acid Synthesis

Summary

This transcript outlines the biochemical process of fatty acid synthesis, highlighting key enzymatic steps that occur in the cytoplasm. Starting with the transport of acetyl-CoA from the mitochondria, the process involves several key enzymes, such as acetyl-CoA carboxylase and fatty acid synthase (FAS), which catalyze reactions like carboxylation, reduction, condensation, and dehydration. The steps ultimately elongate the fatty acid chain, producing a saturated fatty acid. The summary emphasizes the role of ATP, NADPH, biotin, and Coenzyme A, illustrating their crucial roles in driving and regulating the pathway.

Takeaways

• 😀 The process of fatty acid synthesis takes place in the cytoplasm of cells, using acetyl-CoA as the building block for fatty acids.
• 😀 Acetyl-CoA molecules are initially formed in the mitochondria but must be transported to the cytoplasm for fatty acid synthesis.
• 😀 High levels of citrate and ATP in the cytoplasm promote the synthesis of fatty acids by committing acetyl-CoA to the process.
• 😀 The enzyme acetyl-CoA carboxylase catalyzes the first key step in fatty acid synthesis, adding a carbon dioxide to acetyl-CoA to form malonyl-CoA.
• 😀 Biotin (vitamin B7) plays a critical role in attaching and transferring carbon dioxide in the formation of malonyl-CoA.
• 😀 The carboxylation of acetyl-CoA to form malonyl-CoA is the rate-limiting step in fatty acid synthesis and is tightly regulated.
• 😀 The fatty acid synthase (FAS) enzyme is a large polypeptide chain containing multiple catalytic domains that work sequentially to build the fatty acid chain.
• 😀 The first step of fatty acid chain elongation involves transferring an acetyl group from acetyl-CoA onto the ACP (acyl carrier protein) domain of FAS.
• 😀 The second step involves transferring the acetyl group to a cysteine residue on the FAS enzyme, preparing it for the next elongation steps.
• 😀 Malonyl-CoA is used as a key building block for elongating the fatty acid chain, with malonyl-CoA transferring its group to the ACP domain in the third step.
• 😀 The condensation step in fatty acid synthesis removes carbon dioxide and drives the reaction forward, promoting the elongation of the fatty acid chain.
• 😀 In subsequent steps, reduction (using NADPH) and dehydration reactions convert the intermediates into a saturated fatty acid chain.
• 😀 The final product after a series of reduction and dehydration reactions is a fatty acid with a saturated carbon chain.

Q & A

What is the first step in the process of fatty acid synthesis?

The first step is the transport of acetyl-CoA from the mitochondria to the cytoplasm, where fatty acid synthesis occurs.

Why is the carboxylation of acetyl-CoA important in fatty acid synthesis?

The carboxylation of acetyl-CoA is a crucial step because it converts acetyl-CoA into malonyl-CoA, which is necessary for elongating the fatty acid chain. This step also commits acetyl-CoA to fatty acid synthesis.

What role does ATP play in the carboxylation step of fatty acid synthesis?

ATP provides the energy required to attach a carbon dioxide molecule to acetyl-CoA, forming malonyl-CoA.

What is the function of biotin in the carboxylation step?

Biotin acts as a cofactor in the carboxylation reaction, facilitating the binding of carbon dioxide to acetyl-CoA to form malonyl-CoA.

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

Acetyl-CoA carboxylase is a key enzyme in fatty acid synthesis as it catalyzes the conversion of acetyl-CoA to malonyl-CoA. It is also the rate-limiting step in the process, meaning it regulates the overall speed of fatty acid production.

How does the fatty acid synthase (FAS) enzyme contribute to fatty acid synthesis?

Fatty acid synthase is a large enzyme complex that catalyzes the elongation of fatty acid chains. It has several catalytic domains, including ones for acetyl transfer, malonyl transfer, condensation, reduction, dehydration, and a second reduction step.

What is the role of malonyl-CoA in the elongation of fatty acid chains?

Malonyl-CoA provides two-carbon units that are added to the growing fatty acid chain during the elongation cycle, ultimately increasing the length of the fatty acid.

What happens during the condensation step of fatty acid synthesis?

During the condensation step, the acetyl and malonyl groups react, releasing carbon dioxide and forming a longer fatty acid chain. This step is energetically favorable, helping drive the reaction forward.

What is the purpose of the reduction steps in fatty acid synthesis?

The reduction steps convert a carbonyl group to an alcohol (via NADPH) and then reduce double bonds to single bonds, ensuring that the fatty acid chain becomes fully saturated with hydrogen atoms.

How is the double bond in the fatty acid chain removed during synthesis?

The dehydration step removes water from the fatty acid chain, forming a double bond between two carbon atoms. This is followed by a second reduction step to reduce the double bond to a single bond.