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Questions and Answers
What is the primary function of the microsomal pathway in fatty acid elongation?
What is the primary function of the microsomal pathway in fatty acid elongation?
What molecule acts as the acetyl donor in the microsomal pathway of fatty acid elongation?
What molecule acts as the acetyl donor in the microsomal pathway of fatty acid elongation?
During myelination of nerves, which fatty acid lengths are primarily produced by the microsomal pathway?
During myelination of nerves, which fatty acid lengths are primarily produced by the microsomal pathway?
What is the main function of glycerol-3-phosphate in lipogenesis?
What is the main function of glycerol-3-phosphate in lipogenesis?
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What is the primary role of insulin in lipogenesis?
What is the primary role of insulin in lipogenesis?
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Which hormone is primarily responsible for inhibiting lipogenesis and stimulating lipolysis during fasting?
Which hormone is primarily responsible for inhibiting lipogenesis and stimulating lipolysis during fasting?
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In which tissue(s) is lipogenesis primarily regulated by the interplay of insulin and glucagon?
In which tissue(s) is lipogenesis primarily regulated by the interplay of insulin and glucagon?
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What is the primary cause of fatty liver disease?
What is the primary cause of fatty liver disease?
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What is the main product of the cytoplasmic pathway of fatty acid synthesis?
What is the main product of the cytoplasmic pathway of fatty acid synthesis?
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What enzyme is key in regulating the cytoplasmic pathway of fatty acid synthesis?
What enzyme is key in regulating the cytoplasmic pathway of fatty acid synthesis?
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Which of the following conditions inhibits fatty acid synthesis?
Which of the following conditions inhibits fatty acid synthesis?
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What is formed when acetyl CoA is activated during fatty acid synthesis?
What is formed when acetyl CoA is activated during fatty acid synthesis?
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Where does fatty acid synthesis take place within the cell?
Where does fatty acid synthesis take place within the cell?
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Which of the following substrates is NOT required for fatty acid synthesis?
Which of the following substrates is NOT required for fatty acid synthesis?
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What role does citrate play in fatty acid synthesis?
What role does citrate play in fatty acid synthesis?
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What are the main reactions involved in fatty acid synthesis?
What are the main reactions involved in fatty acid synthesis?
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Study Notes
Fatty Acid Synthesis
- There are two mechanisms for fatty acid synthesis: cytoplasmic and microsomal.
- The cytoplasmic system (extra-mitochondrial) or de novo pathway produces palmitate (16C) as its main product.
- This pathway takes place in the cytosol of many tissues, including the liver, adipose tissue, lung, and kidney.
- It requires acetyl CoA, NADPH+H, and a group of enzymes called fatty acid synthase complex.
Fatty Acid Synthesis Pathway
- Stage 1: Transport of acetyl CoA out of the mitochondria into the cytoplasm via citrate, which is cleaved into oxaloacetate and acetyl CoA.
- Stage 2: Activation of acetyl CoA to form malonyl CoA.
- Stage 3: Repetitive addition and reduction of two-carbon units to synthesize C16 fatty acid on an acyl carrier protein.
Regulation of Fatty Acid Synthesis
- Insulin stimulates fatty acid synthesis.
- Glucagon and epinephrine inhibit fatty acid synthesis through cyclic AMP and stimulate lipolysis.
- Long-chain acyl CoA inhibits fatty acid synthesis.
- Citrate stimulates fatty acid synthesis through stimulation of acetyl CoA carboxylase.
Microsomal Pathway
- This pathway is responsible for the elongation of existing long-chain fatty acid molecules (C10-C16) derived from palmitate and dietary fatty acids.
- It requires malonyl CoA as an acetyl donor and NADPH+H as a coenzyme.
- This system is active during myelination of nerves, providing C22 and C24 fatty acids for sphingolipids.
Lipogenesis
- Lipogenesis is the synthesis of triacylglycerols from fatty acids (acyl CoA) and glycerol (glycerol-3-phosphate).
- Steps:
- Activation of fatty acids into fatty acyl CoA.
- Synthesis of glycerol phosphate in liver, kidney, intestine, and muscle.
- Synthesis of triacylglycerol by reaction between acyl CoA and glycerol phosphate.
Regulation of Lipogenesis
- After a meal, lipogenesis is stimulated by insulin, which stimulates glycolysis, providing dihydroxyacetone phosphate that is converted into glycerol phosphate in adipose tissue.
- During fasting, lipogenesis is inhibited by anti-insulin hormones (e.g., glucagon), which inhibit lipogenesis and stimulate lipolysis.
Fatty Liver
- Fatty liver disease is a build-up of fats in the liver, which can damage the organ and lead to serious complications.
- Normally, liver cells contain only 5% of fats.
- Fatty liver is formed when fat levels increase above 5% in liver cells due to an imbalance in the rate of triacylglycerol synthesis and export.
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Description
Understand the two mechanisms of fatty acid synthesis, including cytoplasmic and microsomal pathways, and their products and locations in the body.
