Fatty Acid Synthesis Pathway – Biochemistry & Significance
The fatty acid synthesis pathway is the biochemical process by which the body builds new fatty acids from acetyl-CoA. It plays a central role in metabolism and energy storage.
Things worth knowing about "Fatty Acid Synthesis Pathway"
The fatty acid synthesis pathway is the biochemical process by which the body builds new fatty acids from acetyl-CoA. It plays a central role in metabolism and energy storage.
What Is the Fatty Acid Synthesis Pathway?
The fatty acid synthesis pathway, also known as lipogenesis or de novo fatty acid synthesis, is a fundamental biochemical metabolic pathway through which the human body synthesizes long-chain fatty acids from simple precursor molecules, primarily acetyl-CoA. This process takes place mainly in the liver, but also in adipose tissue and mammary glands, and occurs predominantly in the cytoplasm of cells.
The fatty acid synthesis pathway is particularly active when the body receives more energy (e.g., from carbohydrates) than it currently needs. The surplus energy is then stored in the form of fatty acids.
Steps of the Fatty Acid Synthesis Pathway
The pathway proceeds through a series of sequential steps catalyzed by the enzyme complex Fatty Acid Synthase (FAS):
- Activation: Acetyl-CoA is carboxylated by the enzyme Acetyl-CoA Carboxylase to form Malonyl-CoA. This is the rate-limiting step, promoted by insulin and inhibited by glucagon and AMP-activated protein kinase (AMPK).
- Transfer: Acetyl-CoA and Malonyl-CoA are transferred to the Acyl Carrier Protein (ACP) domain of the FAS complex.
- Chain elongation: In each cycle, the growing fatty acid chain is extended by two carbon atoms. Each cycle involves four enzymatic reactions: condensation, reduction, dehydration, and a second reduction.
- Release: After seven cycles, the saturated fatty acid palmitic acid (C16:0) is produced as the main product and cleaved from the FAS complex.
Energy Requirements and Cofactors
The fatty acid synthesis pathway is an energy-consuming (endergonic) process. The synthesis of one molecule of palmitic acid requires:
- 8 molecules of acetyl-CoA
- 7 molecules of ATP
- 14 molecules of NADPH (primarily derived from the pentose phosphate pathway)
Regulation of the Fatty Acid Synthesis Pathway
Regulation occurs at multiple levels:
- Hormonal control: Insulin promotes fatty acid synthesis by activating Acetyl-CoA Carboxylase. Glucagon and epinephrine inhibit the pathway.
- Allosteric regulation: Citrate activates Acetyl-CoA Carboxylase, while palmitoyl-CoA inhibits it (product inhibition).
- Transcriptional control: The transcription factor SREBP-1c (Sterol Regulatory Element-Binding Protein 1c) regulates the gene expression of enzymes involved in the fatty acid synthesis pathway.
Clinical Significance
Dysregulation of the fatty acid synthesis pathway is associated with several diseases:
- Obesity and metabolic syndrome: Excessive activity of the pathway, particularly in the context of high carbohydrate intake, can contribute to fat accumulation and the development of overweight.
- Non-alcoholic fatty liver disease (NAFLD): Increased hepatic lipogenesis is a key mechanism in the development of fatty liver disease.
- Cancer: Many tumor cells show significantly elevated expression of Fatty Acid Synthase (FAS), making it a potential target for novel cancer therapies.
- Type 2 diabetes: Insulin resistance substantially affects the regulation of the fatty acid synthesis pathway.
Therapeutic Approaches
Due to its clinical relevance, the fatty acid synthesis pathway is an active area of research. Inhibitors of Acetyl-CoA Carboxylase and Fatty Acid Synthase are being investigated as potential therapeutic agents for obesity, type 2 diabetes, and certain cancers.
References
- Berg JM, Tymoczko JL, Stryer L. Biochemistry. 9th edition. W.H. Freeman and Company, 2019.
- Lodish H et al. Molecular Cell Biology. 9th edition. W.H. Freeman and Company, 2021.
- Strable MS, Ntambi JM. Genetic control of de novo lipogenesis: role in diet-induced obesity. Critical Reviews in Biochemistry and Molecular Biology, 2010; 45(3): 199-214.
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