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The majority of fatty acids required by the body are supplied by the diet.
The majority of fatty acids required by the body are supplied by the diet.
True
Which of the following tissues are the primary sites for fatty acid synthesis in humans? (Select all that apply)
Which of the following tissues are the primary sites for fatty acid synthesis in humans? (Select all that apply)
Fatty acid synthesis is a simple reversal of the degradative pathway.
Fatty acid synthesis is a simple reversal of the degradative pathway.
False
Which of the following is NOT a key difference between the biosynthesis and degradation pathways of fatty acids?
Which of the following is NOT a key difference between the biosynthesis and degradation pathways of fatty acids?
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What molecule acts as a primer in fatty acid biosynthesis and forms the carbon atoms 15 and 16 of palmitate?
What molecule acts as a primer in fatty acid biosynthesis and forms the carbon atoms 15 and 16 of palmitate?
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What is the other key molecule, besides acetyl-CoA, involved in the elongation of the fatty acid chain, adding a 2-carbon unit by a process called malonyl-CoA formation?
What is the other key molecule, besides acetyl-CoA, involved in the elongation of the fatty acid chain, adding a 2-carbon unit by a process called malonyl-CoA formation?
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Fatty acid synthesis involves the transfer of substrates to the cytosol, but mitochondria lack the necessary permeability for acetyl-CoA to cross directly.
Fatty acid synthesis involves the transfer of substrates to the cytosol, but mitochondria lack the necessary permeability for acetyl-CoA to cross directly.
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What is the rate-limiting enzyme in fatty acid biosynthesis?
What is the rate-limiting enzyme in fatty acid biosynthesis?
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Acetyl-CoA carboxylase is activated by high levels of palmitoyl-CoA and inhibited by the presence of citrate.
Acetyl-CoA carboxylase is activated by high levels of palmitoyl-CoA and inhibited by the presence of citrate.
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The free palmitate, the product of fatty acid synthase, is ready to directly participate in other metabolic pathways.
The free palmitate, the product of fatty acid synthase, is ready to directly participate in other metabolic pathways.
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Which of the following is NOT a primary fate of palmitate?
Which of the following is NOT a primary fate of palmitate?
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Elongation and desaturation of fatty acids can only occur in microsomes of the endoplasmic reticulum.
Elongation and desaturation of fatty acids can only occur in microsomes of the endoplasmic reticulum.
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Which molecule is responsible for transporting fatty acids from mitochondria to the cytosol?
Which molecule is responsible for transporting fatty acids from mitochondria to the cytosol?
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In the mitochondrial elongation pathway, the source of the 2-carbon units is malonyl-CoA.
In the mitochondrial elongation pathway, the source of the 2-carbon units is malonyl-CoA.
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The synthesis of triacylglycerols in liver and adipose tissue relies entirely on the same mechanism, relying on the same source of glycerol-3-phosphate.
The synthesis of triacylglycerols in liver and adipose tissue relies entirely on the same mechanism, relying on the same source of glycerol-3-phosphate.
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What is the name of the enzyme that breaks down triacylglycerol stored in adipose tissue?
What is the name of the enzyme that breaks down triacylglycerol stored in adipose tissue?
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Glycerol released from triacylglycerol hydrolysis in adipose tissue can efficiently be utilized by adipocytes for energy production.
Glycerol released from triacylglycerol hydrolysis in adipose tissue can efficiently be utilized by adipocytes for energy production.
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Hormone-sensitive lipase exhibits greater activity in the presence of insulin and glucose.
Hormone-sensitive lipase exhibits greater activity in the presence of insulin and glucose.
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Which of the following is NOT a class of phospholipids?
Which of the following is NOT a class of phospholipids?
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The synthesis of glycerophospholipids shares the initial steps with the synthesis of triacylglycerols.
The synthesis of glycerophospholipids shares the initial steps with the synthesis of triacylglycerols.
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What is the activated phosphatidyl unit that forms the backbone for the synthesis of phosphatidylserine and phosphatidylinositol?
What is the activated phosphatidyl unit that forms the backbone for the synthesis of phosphatidylserine and phosphatidylinositol?
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The synthesis of phosphatidylcholine can only occur via the CDP-choline pathway.
The synthesis of phosphatidylcholine can only occur via the CDP-choline pathway.
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What is the molecule that provides the methyl group for the methylation of ethanolamine to form choline?
What is the molecule that provides the methyl group for the methylation of ethanolamine to form choline?
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Which of the following is NOT a type of glycolipid?
Which of the following is NOT a type of glycolipid?
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Ceramide is the primary component of glycosphingolipids, forming the backbone for the synthesis of these complex lipids.
Ceramide is the primary component of glycosphingolipids, forming the backbone for the synthesis of these complex lipids.
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What sugar is typically linked to ceramide to form galactocerebroside?
What sugar is typically linked to ceramide to form galactocerebroside?
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Gangliosides, the most complex glycolipids, consist of a linear chain of oligosaccharides.
Gangliosides, the most complex glycolipids, consist of a linear chain of oligosaccharides.
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What is the name of the activated sugar that is commonly added to ceramide during the synthesis of gangliosides?
What is the name of the activated sugar that is commonly added to ceramide during the synthesis of gangliosides?
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The synthesis of sphingomyelin requires the formation of ceramide as an intermediate step.
The synthesis of sphingomyelin requires the formation of ceramide as an intermediate step.
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What is the name of the molecule that reacts with ceramide to form sphingomyelin?
What is the name of the molecule that reacts with ceramide to form sphingomyelin?
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Study Notes
De Novo Synthesis of Fatty Acids (Lipogenesis)
- Fatty acids are synthesized when there is excess calorie intake.
- Synthesis occurs mainly in the liver and lactating mammary glands, and to a lesser extent, in adipose tissue, kidneys, and brain.
- This process involves new reactions, not a reversal of degradation pathways.
Biosynthesis of Fatty Acids
- Occurs in the cytosol.
- Intermediates are linked to acyl carrier protein (ACP).
- Enzymes are joined in a single polypeptide chain, forming fatty acid synthase.
- Reducing equivalents involved include NADPH.
- Fatty acids are synthesized through elongation, adding two-carbon units (acetyl-CoA) in the form of malonyl-CoA sequentially, to the carboxyl end of the growing chain.
- CO2 participates in forming malonyl-CoA from acetyl-CoA.
- The stereosomeric form of hydroxyacyl is D(-).
- Acetyl-CoA forms carbon atoms 15 and 16 of palmitate.
- Subsequent 2-C units are added via malonyl-CoA formation.
Phases of De Novo Fatty Acid Synthesis
- Phase 1: Transport of substrates into the cytosol and carboxylation of acetyl-CoA to malonyl-CoA by acetyl-CoA carboxylase.
- Phase 2: Utilization of substrate to form palmitate by fatty acid synthase.
- Phase 3: Elongation and desaturation of palmitate to form other fatty acids.
Transport of Acetyl-CoA from Mitochondria to Cytosol
- Citrate is formed from acetyl-CoA and oxaloacetate in the mitochondrial matrix.
- Citrate is transported to the cytosol by a translocase.
- Citrate lyase cleaves citrate into oxaloacetate and acetyl-CoA in the cytosol.
- Oxaloacetate is returned to the mitochondria.
Carboxylation of Acetyl-CoA to Malonyl-CoA
- Acetyl-CoA carboxylase catalyzes this irreversible reaction, using bicarbonate as a CO2 source and ATP.
- Acetyl-CoA carboxylase is an allosteric enzyme, activated by citrate and inhibited by palmitoyl-CoA.
Fatty Acid Synthase Complex
- A multienzyme complex containing seven enzyme activities.
- Includes an acyl carrier protein (ACP) for the growing chain's attachment.
- Each monomer has all seven activities of the reaction sequence.
Reactions of Phase 2
- Acetyl group from acetyl-CoA is transferred to the enzyme complex.
- Malonyl group from malonyl-CoA is transferred to ACP.
- Condensation, reduction, dehydration and saturation reactions sequentially elongate the chain by two carbons.
Fate of Palmitate
- Palmitate is activated to acyl-CoA before further metabolism.
- Esterified into acylglycerols or
- Precursor for other longer-chain fatty acids.
Chain Elongation and Desaturation
- Elongation and desaturation of fatty acids occur in the endoplasmic reticulum and mitochondria.
- Elongation uses malonyl-CoA, and NADPH for reducing equivalents.
Regulation of Fatty Acid Synthesis
- Acetyl-CoA carboxylase is the rate-limiting enzyme in fatty acid synthesis, regulated by:
- Allosteric regulation: Citrate activates; palmitoyl-CoA inhibits.
- Hormonal regulation: Insulin activates; glucagon and epinephrine inhibit.
- Nutritional regulation: High carbohydrate diets stimulate; high fat diets inhibit.
Synthesis of Triacylglycerols
- Triacylglycerols are produced in the liver and adipose tissue from glycerol-3-phosphate and activated fatty acids (acyl-CoA).
- Two acyl-CoAs combine with glycerol 3-phosphate to form phosphatidic acid, then diacylglycerol, ultimately triacylglycerol.
- The fates of triacylglycerols differ in liver (primarily exported as VLDL) and adipose tissue (storage).
Phospholipid Metabolism
- Phospholipids are major membrane lipids, with glycerol- and sphingo- based structures.
- Glycerophospholipid synthesis involves starting with glycerol-3-phosphate, and successive additions of activated fatty acids (acyl-CoA) to form phosphatidic acid.
- Various phospholipid types, including phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, cardiolipin and plasmalogens are formed through similar processes.
Synthesis of Glycolipids
- Glycolipids are sugar-containing lipids.
- Cerebrosides, sulfatides, globosides, and gangliosides are important types of glycolipids.
- Cerebroside formation begins with ceramide, adding UDP-glucose or UDP-galactose to form glucocerebroside or galactocerebroside, respectively.
Synthesis of Sphingomyelin
- Sphingomyelin is a sphingolipid.
- The synthesis starts with condensation of palmitoyl-CoA and serine, followed by reactions to form sphingosine and ceramide.
- Ceramide combines with phosphatidylcholine in the Golgi to produce sphingomyelin.
Synthesis of Gangliosides
- Gangliosides are complex glycolipids with a branched chain oligosaccharide.
- Ganglioside synthesis involves stepwise addition of activated sugars (e.g., UDP-glucose, UDP-galactose) and sialic acid (NANA) to ceramide.
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Description
This quiz covers the de novo synthesis of fatty acids, also known as lipogenesis. It discusses the key processes involved in fatty acid biosynthesis, including the role of enzymes, intermediates, and the significance of acetyl-CoA. Understand the phases and mechanisms critical for fatty acid production in various tissues.
