Fatty Acid Synthesis and Metabolism Quiz
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Questions and Answers

What characterizes a saturated fatty acid?

  • It contains a mix of saturated and unsaturated bonds.
  • It has all carbon atoms fully saturated with hydrogen. (correct)
  • It lacks hydrogen atoms on every carbon.
  • It contains only double bonds between carbons.

Which tissues primarily express saturated fatty acids?

  • Adipose tissue and the liver. (correct)
  • Cardiac tissue and nervous tissue.
  • Muscle tissue and bone.
  • Connective tissue and skin.

What is the product of the first round of elongation in fatty acid synthesis?

  • Hexanoic acid.
  • Butyryl ACP. (correct)
  • Palmitic acid.
  • Acetoacetyl ACP.

How many cycles of elongation are performed to form palmitoyl ACP?

<p>Seven cycles. (D)</p> Signup and view all the answers

What is the role of acyl-malonyl ACP condensing enzyme in the fatty acid synthesis process?

<p>It initiates the condensation reaction. (D)</p> Signup and view all the answers

During the first phase of fatty acid synthesis, what is formed after the reduction of acetoacetyl ACP?

<p>D-3-hydroxybutyryl ACP. (A)</p> Signup and view all the answers

What is the importance of the hydration step in the fatty acid synthesis process?

<p>It allows for the transformation of crotonyl ACP. (B)</p> Signup and view all the answers

Which of the following best describes the elongation of fatty acid chains?

<p>Each cycle adds two carbons to the carbon chain. (B)</p> Signup and view all the answers

What type of metabolism is primarily utilized by neuronal cells in the brain?

<p>Aerobic metabolism (C)</p> Signup and view all the answers

What is a significant feature of glial cell metabolism?

<p>It is primarily anaerobic (A)</p> Signup and view all the answers

Which compound is a master regulator of mitochondrial function and biogenesis that is downregulated in ALS patients?

<p>PGC-1α (B)</p> Signup and view all the answers

What metabolic change occurs in ALS patient muscle concerning oxidative stress?

<p>Oxidative stress is elevated due to lipid-centric pathways (D)</p> Signup and view all the answers

What is the consequence of increased demand for energy on motor neurons in ALS?

<p>Increased reliance on alternative fuel sources (C)</p> Signup and view all the answers

How does the metabolism of glucose change in the brains of ALS patients?

<p>Glucose metabolism is significantly decreased (D)</p> Signup and view all the answers

What potential outcome might result from increased oxidative stress in the ALS-affected brain?

<p>Several deleterious effects on neuronal health (B)</p> Signup and view all the answers

What happens to lactate transport and metabolism in ALS?

<p>Lactate transport and metabolism are reduced (A)</p> Signup and view all the answers

What is the final product of the divergent synthesis pathways discussed?

<p>Cholesterol (A)</p> Signup and view all the answers

Which pathway is primarily favored by neuronal cells for cholesterol synthesis?

<p>Kandutsch-Russell pathway (C)</p> Signup and view all the answers

Which of the following statements about cholesterol transport in the CNS is true?

<p>Cholesterol is packaged into HDLs for return to the liver. (C)</p> Signup and view all the answers

What happens to cholesterol after it is synthesized?

<p>It can be converted into bile acids or steroid hormones. (B)</p> Signup and view all the answers

Which statement about lanosterol levels in neuronal and astrocytic cells is correct?

<p>Lanosterol levels are much higher in neurons compared to astrocytes. (D)</p> Signup and view all the answers

Which process is essential for converting squalene to lanosterol?

<p>Cyclization (D)</p> Signup and view all the answers

What determines the specific pathway for cholesterol synthesis in an individual cell?

<p>The nature of the hydrocarbon chain (D)</p> Signup and view all the answers

Why is the concentration of cholesterol at the endoplasmic reticulum typically low?

<p>Due to rapid intracellular transport of cholesterol to appropriate membranes. (B)</p> Signup and view all the answers

What is the primary role of phosphatidylcholine in cell membranes?

<p>It contributes to the structural integrity of cell membranes. (D)</p> Signup and view all the answers

During periods of fasting, how is fatty acid-derived acetyl-CoA primarily utilized in the brain?

<p>It is preferentially shuttled into ketone body formation. (C)</p> Signup and view all the answers

How does the geometry of phosphatidylcholine affect cell membranes?

<p>It allows for varying levels of membrane permeability. (B)</p> Signup and view all the answers

What is the relationship between glucose usage and ATP generation in the brain?

<p>Glucose must be used as the obligate substrate for ATP production. (C)</p> Signup and view all the answers

Which statement best describes the effect of phosphatidylcholine on membrane curvature?

<p>It does not feature any curvature due to its geometry. (C)</p> Signup and view all the answers

What generally happens to fatty acids during extreme exertion?

<p>They can be utilized as an alternative energy source. (A)</p> Signup and view all the answers

Which complex in the electron transport chain is associated with increased superoxide generation?

<p>Complex I (A)</p> Signup and view all the answers

Which modification of phosphatidylcholine can transform the membrane geometry?

<p>Transformation to phosphatidic acid (C)</p> Signup and view all the answers

What is the reason for the low concentration of cholesterol in the ER?

<p>It allows for easier protein insertion and folding. (C)</p> Signup and view all the answers

What characterizes lipid rafts in cellular membranes?

<p>They serve as anchoring sites for proteins. (C)</p> Signup and view all the answers

How do sphingolipids and cholesterol interact in cellular membranes?

<p>Cholesterol promotes phase separation and raft formation. (B)</p> Signup and view all the answers

Which of the following is an effect of a high concentration of sphingolipids in membranes?

<p>Formation of lipid rafts. (B)</p> Signup and view all the answers

What role do lipids play in cellular signaling processes?

<p>They are involved in numerous signaling pathways. (B)</p> Signup and view all the answers

What is the significance of the 'liquid ordered state' in membranes?

<p>It is essential for the formation of lipid rafts. (A)</p> Signup and view all the answers

Why are lipid rafts thought to promote specific cellular processes?

<p>They serve as sites for protein interactions. (A)</p> Signup and view all the answers

What is the role of sphingolipids in the context of cholesterol in cellular membranes?

<p>They are integral to forming lipid rafts with cholesterol. (B)</p> Signup and view all the answers

What are the three major ketone bodies formed during the ketogenesis pathway?

<p>Acetoacetate, D-3-β-hydroxybutyrate, and propanone (D)</p> Signup and view all the answers

Which component is primarily found on the inner leaflet of the plasma membrane?

<p>Phosphatidylethanolamine (A), Phosphatidylserine (C)</p> Signup and view all the answers

What is the function of ketone bodies upon reaching the brain?

<p>They undergo ketolysis. (D)</p> Signup and view all the answers

How does an increase in phosphatidylethanolamine concentration affect membrane structure?

<p>It increases membrane fluidity. (D)</p> Signup and view all the answers

What is a primary rationale behind ketogenesis?

<p>It is largely facilitated by extrahepatic glucose levels. (C)</p> Signup and view all the answers

What essential processes facilitated by phosphatidylethanolamine are crucial for neuronal function?

<p>Vesicular budding and membrane fusion (B)</p> Signup and view all the answers

What is the outcome of limiting acetyl-CoA synthesis to the liver in relation to brain function?

<p>It reduces oxidative stress in the brain. (D)</p> Signup and view all the answers

Which polyunsaturated fatty acid is mentioned as an essential precursor to numerous neuromodulatory molecules in the brain?

<p>Arachidonic acid (A)</p> Signup and view all the answers

Flashcards

Saturated Fatty Acid

A type of fatty acid where all carbon atoms are linked by single bonds and are ‘saturated’ with hydrogen atoms.

Fatty Acid Synthesis

The process of creating fatty acids (like palmitate)

Acyl-Malonyl ACP Condensing Enzyme

A key enzyme in fatty acid synthesis that helps join acetyl CoA and malonyl CoA to form acetoacetyl CoA.

Acyl Carrier Protein (ACP)

A molecule involved in fatty acid synthesis that carries a growing fatty acid chain.

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Malonyl CoA

A molecule involved in fatty acid synthesis that has a three-carbon chain.

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Dehydration

A step in fatty acid synthesis that involves removing water from a molecule.

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Reduction

A step in fatty acid synthesis that involves adding hydrogen atoms to a molecule.

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Palmitoyl ACP

The product of fatty acid synthesis, a 16-carbon fatty acid.

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Cholesterol Synthesis

The process where a series of enzymatic reactions convert a starting molecule into a final product, specifically, the synthesis of cholesterol.

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Kandutsch-Russell Pathway

The process where cholesterol is synthesized from lanosterol, favored by neurons, resulting in different types of cholesterol.

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Bloch Pathway

The process where cholesterol is synthesized from lanosterol, favored by glial cells, resulting in different types of cholesterol.

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Divergent Pathways in Cholesterol Synthesis

Important in the brain, the divergent pathways of cholesterol synthesis (Kandutsch-Russell & Bloch) lead to distinct cholesterol variants in different neuronal cells.

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Endoplasmic Reticulum (ER)

The primary site of cholesterol synthesis within cells.

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Intracellular Cholesterol Transport

The process of moving cholesterol from the ER to other parts of the cell, since the ER concentration is typically low due to rapid transport.

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High-Density Lipoproteins (HDLs)

High-density lipoproteins that transport extra cholesterol back to the liver from the periphery.

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Cholesterol Transport in the CNS

The process of moving cholesterol between different cell types within the Central Nervous System (CNS) using lipoproteins.

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Ketogenesis

A process in the liver that produces ketone bodies, mainly acetoacetate, D-3-β-hydroxybutyrate, and propanone, during periods of low glucose availability.

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Ketone Bodies

Molecules produced by the liver during ketogenesis that serve as an energy source for the brain when glucose is limited.

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Ketolysis

The process by which the brain uses ketone bodies as fuel.

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Phosphatidylethanolamine

A type of phospholipid found mainly on the inner leaflet of the plasma membrane, often associated with increased membrane curvature and fluidity.

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Arachidonic Acid

The fatty acid, arachidonic acid, which is enriched in phosphatidylethanolamine and serves as a precursor for important molecules like prostaglandins and anandamides.

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Phosphatidylserine

A type of phospholipid primarily found on the inner leaflet of the plasma membrane, playing a role in cell signaling and membrane structure.

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Brain's reliance on glucose

Fatty acids are a rich source of energy for the brain, but their reliance on oxygen for ATP generation can be problematic. Glucose is the preferred fuel source due to the brain's oxygen-centric metabolism.

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Ketone bodies as brain fuel

Ketone bodies are fatty acid derivatives that can be used for energy during fasting or intense periods of exercise. They provide an alternative energy source to protect the brain from potential damage.

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Phosphatidylcholine: Structure of cell membrane

Phosphatidylcholine is a type of phospholipid that makes up a large part of cell membranes. It gives the membrane a cylindrical shape, affecting its fluidity and permeability.

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Phosphatidylcholine and membrane properties

The ratio of phosphatidylcholine to other phospholipids in a membrane can influence its shape and permeability.

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Phosphatidylcholine modifications

Phosphatidylcholine can be modified into other molecules like phosphatidic acid or lysophosphatidylcholine, leading to changes in membrane geometry or permeability.

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Fatty acids and mitochondrial membranes

Mitochondrial membranes are important for ATP generation, but they can be affected by fatty acids. They can decrease oxidative ATP production and increase the generation of harmful superoxide radicals.

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Choline in the brain

The brain uses a lot of choline for neurotransmission, and it is stored in cell membranes primarily as phosphatidylcholine.

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Variety of phospholipids: Functional diversity

Specific subclasses of phospholipids play different roles in cell membranes, with their unique structural characteristics influencing their functions.

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ALS & Neuron Fuel Switch

In ALS, neurons struggle to utilize glucose as fuel, leading to the hypothesis that they turn to alternative sources like lipids for energy.

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Lipid Fuel & Oxidative Stress

When neurons rely heavily on lipids for energy, it also increases oxidative stress, which can have damaging consequences.

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ALS & Decreased Glucose Metabolism

In ALS, the brain and spinal cord show a significant decrease in glucose usage and tricarboxylic acid cycle intermediates, suggesting a shift in energy metabolism.

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PGC-1α in ALS Muscle

A master regulator of mitochondrial function and biogenesis, PGC-1α, is downregulated in ALS muscle, affecting fatty acid signaling and increasing β-oxidation.

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PGC-1α & ALS Progression

Downregulation of PGC-1α in mouse models of ALS has been shown to accelerate disease progression, suggesting its importance in ALS pathogenesis.

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PGC-1α & ALS Maintenance

Upregulation of PGC-1α in mouse models of ALS has been shown to help maintain the health of the disease, suggesting its potential as a therapeutic target.

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Glial Cells & Anaerobic Metabolism

In ALS, glial cells, unlike neurons, primarily rely on anaerobic metabolism for energy, using glucose/lactate as their fuel.

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Oxidative Stress in Normal & ALS Neurons

During normal neuronal activity, oxidative stress is kept relatively low; however, increased energy demands in ALS elevate oxidative stress levels.

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Cholesterol-Sphingolipid Affinity

The preferential attraction of cholesterol to sphingolipids compared to phospholipids.

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Lipid Rafts

Lipid rafts are microdomains within cell membranes enriched in sphingolipids and cholesterol. They act as platforms for specific protein interactions and signaling.

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Phase Separation

The process by which sphingolipids and cholesterol cluster together in membranes, separating them from the phospholipids. This creates distinct regions with unique properties.

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Sphingolipid and Cholesterol Gradient

Sphingolipids and cholesterol are more concentrated in the plasma membrane and endosomes compared to the endoplasmic reticulum (ER).

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Membrane Fluidity

The ability of membranes to change their fluidity based on the concentration of specific lipids like sphingolipids and cholesterol. This affects how easily molecules can pass through.

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Lipid Signaling in the CNS

The process of lipids, particularly sphingolipids and cholesterol, influencing the signaling pathways within nerve cells.

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Lipid Raft-Mediated Signaling

A specialized type of signaling pathway that is triggered by the binding of specific molecules to receptor proteins located in lipid rafts.

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Lipid Raft Functions in the CNS

Lipid rafts are involved in a variety of processes in the brain, including sorting of molecules within cells and regulating the response of neurons to specific signals.

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Study Notes

Neuronal Lipid Metabolism

  • Lipids are a fundamental class of organic molecules
  • Classified into fatty acids, triacylglycerols (TAGs), phospholipids, sterol lipids, and sphingolipids
  • Different lipid classes have diverse functions in neurons, including energy substrates, structural components, and bioactive molecules
  • Lipid metabolism dysfunction is a potential driver of neurodegenerative diseases like amyotrophic lateral sclerosis (ALS)

Lipid Synthesis, Structure, and Transport

  • Fatty acid synthesis primarily occurs in the endoplasmic reticulum (ER)
  • Fatty acids can be saturated or unsaturated
  • Unsaturated fatty acids (PUFAs) are essential for brain function and membrane structure
  • Fatty acids are synthesized in the cytosol of lipogenic tissues.
  • The brain can synthesize most saturated and monounsaturated fatty acids, but lacks the ability to synthesize polyunsaturated fatty acids (PUFAs)
  • Fatty acids are transported across cell membranes via passive diffusion, FATP (fatty acid transport protein), fatty acid translocase/CD36, fatty acid-binding proteins (FABPs), and caveolae
  • TAGs are composed of a glycerol backbone with three fatty acid chains.
  • Their composition can vary, affecting their physical properties
  • TAG synthesis mainly occurs in adipose tissue and the liver, but also in skeletal muscle, kidney, lung, heart, and brain
  • Lipolysis is the breakdown of TAGs, releasing fatty acids
  • The brain receives fatty acids through passive diffusion or transport proteins

Phospholipids

  • Composed of a glycerol backbone, a hydrophobic fatty acid tail, a hydrophilic head group, and a phosphate group
  • Categorized into glycerophospholipids (phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, phosphatidylglycerol, and cardiolipin) and phosphosphingolipids
  • Synthesis primarily occurs in the endoplasmic reticulum (ER)
  • Phospholipids are crucial for maintaining membrane structure and function

Sterol Lipids

  • Sterol lipids, primarily cholesterol, are essential for membrane fluidity and structural integrity
  • Cholesterol synthesis occurs via the mevalonate pathway, a multistep process regulated by HMG-CoA reductase
  • Cholesterol is transported through lipoproteins

Sphingolipids

  • Characterized by a sphingosine backbone; may have additional head groups like phosphocholine (sphingomyelins) or sugars (glycosphingolipids)
  • Synthesis occurs in the endoplasmic reticulum (ER) and Golgi apparatus
  • Sphingolipids play vital roles in cell signaling and membrane organization

Lipid Functions in Neurons

  • Lipids are crucial energy substrates for the brain, though glucose is the primary energy source
  • Lipids serve crucial structural roles in maintaining neuronal membrane integrity and facilitating signaling processes
  • Lipid involvement in signaling pathways (e.g. inflammatory responses, endocannabinoid systems)

Neuronal Lipid Metabolism in Amyotrophic Lateral Sclerosis (ALS)

  • Dysfunction in lipid metabolism is linked to ALS, affecting energy substrates, structural integrity, and signaling processes
  • Altered lipid metabolism contributes to oxidative stress, inflammation, mitochondrial dysfunction, excitotoxicity, neuromuscular junction (NMJ) denervation, and impaired transport
  • Targeting lipid metabolism appears a promising avenue for potential ALS treatment

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Description

Test your knowledge on saturated fatty acids and their roles in metabolism. This quiz covers key processes in fatty acid synthesis, including elongation cycles and the metabolic characteristics of neuronal and glial cells. Enhance your understanding of fatty acid metabolism and its implications in conditions like ALS.

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