Biochemistry of Lipids and Lipoproteins
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Questions and Answers

Which lipid is a major component of myelin?

  • Gangliosides
  • Ceramide
  • Galactocerebroside (correct)
  • Glucocerebroside

    • Glucocerebroside is synthesized from ceramide using UDP-galactose.

    False

    What is formed when Galactocerebroside reacts with PAPS?

    Sulfogalactocerebroside

    Ceramide can react with __________ to form globosides.

    <p>UDP-sugars</p> Signup and view all the answers

    Match the following glycolipids with their descriptions:

    <p>Galactocerebroside = Major lipid of myelin Glucocerebroside = Precursor of complex glycosphingolipids Gangliosides = More complex glycolipids with branched chains Sulfogalactocerebroside = Product of Galactocerebroside and PAPS reaction</p> Signup and view all the answers

    What is the primary role of lipoprotein lipase in the bloodstream?

    <p>To hydrolyze triacylglycerol in VLDL</p> Signup and view all the answers

    Glycerol released in adipose tissue can be metabolized by adipocytes.

    <p>False</p> Signup and view all the answers

    What molecules are triacylglycerol packaged with in the liver to form VLDL?

    <p>Cholesterol, phospholipids, and apolipoproteins (apoB-100)</p> Signup and view all the answers

    The enzyme responsible for hydrolyzing triacylglycerol in adipose tissue is called ___________.

    <p>hormone sensitive lipase</p> Signup and view all the answers

    Match the following phospholipids with their types:

    <p>Phosphatidylserine = Glycerolphospholipid Sphingomyelin = Sphingophospholipid Cardiolipin = Glycerolphospholipid Phosphatidylcholine = Glycerolphospholipid</p> Signup and view all the answers

    Which hormones stimulate hormone sensitive lipase activity?

    <p>Epinephrine and norepinephrine</p> Signup and view all the answers

    What is the fate of glycerol released from triacylglycerol hydrolysis in adipose tissue?

    <p>It is transported to the liver for phosphorylation.</p> Signup and view all the answers

    Phosphatidylethanolamine is an example of a sphingophospholipid.

    <p>False</p> Signup and view all the answers

    Which enzyme is responsible for converting glycerol to glycerol-3-phosphate?

    <p>Glycerol Kinase</p> Signup and view all the answers

    Adipose tissue can synthesize glycerol-3-phosphate from glycerol via glycerol kinase.

    <p>False</p> Signup and view all the answers

    What is the main fate of triacylglycerol in the liver?

    <p>Export as very low density lipoprotein (VLDL)</p> Signup and view all the answers

    What is the primary donor of the two carbon units during the elongation of palmitoyl-CoA?

    <p>Malonyl-CoA</p> Signup and view all the answers

    In adipose tissue, triacylglycerol serves as __________ fat, ready for mobilization.

    <p>depot</p> Signup and view all the answers

    Mammals can synthesize linoleic and linolenic acids endogenously.

    <p>False</p> Signup and view all the answers

    What fatty acid is produced from the elongation of palmitoyl-CoA (C16)?

    <p>Stearyl-CoA (C18)</p> Signup and view all the answers

    Match the following substrates or enzymes with their corresponding products:

    <p>Glycerol + ATP = Glycerol-3-Phosphate 1,2 Diacylglycerol Phosphate = Phosphatidylserine Phosphatidylinositol 4,5-biphosphate = Diacylglycerol + Inositoltriphosphate Diacylglycerol = Triacylglycerol</p> Signup and view all the answers

    Elongation of stearyl-CoA in the brain occurs rapidly during ______ in order to provide C20 and C24 fatty acids.

    <p>myelination</p> Signup and view all the answers

    What is the initial compound from which phosphatidate is synthesized?

    <p>Glycerol-3-phosphate</p> Signup and view all the answers

    Which of the following substances cannot be produced by adipose tissue?

    <p>Glycerol-3-phosphate from glycerol</p> Signup and view all the answers

    The conversion of diacylglycerol to triacylglycerol involves the addition of another acyl-CoA molecule.

    <p>True</p> Signup and view all the answers

    Match the following fatty acids with their characteristics:

    <p>Palmitoleic acid = C16 with one cis double bond Oleic acid = C18 with one cis double bond Linoleic acid = Essential fatty acid (C18:2 Δ9,12) Linolenic acid = Essential fatty acid (C18:3 Δ^9,12,15)</p> Signup and view all the answers

    Phosphatidylcholine is formed directly from CDP-choline without any other intermediate steps.

    <p>False</p> Signup and view all the answers

    Which lipid is formed from the reaction of phosphatidate with cytidine triphosphate (CTP)?

    <p>Cytidine diacylglycerol</p> Signup and view all the answers

    What is the primary source of glycerol-3-phosphate in liver tissue?

    <p>Phosphorylation of glycerol or reduction of dihydroxyacetone phosphate (DHAP)</p> Signup and view all the answers

    Which enzyme is involved in the conversion of palmitoyl-CoA to 3-Hydroxyacyl-CoA?

    <p>3-Ketoacyl Reductase</p> Signup and view all the answers

    Mitochondrial elongation of fatty acids is more active than microsomal elongation.

    <p>False</p> Signup and view all the answers

    Phosphatidylinositol is transformed into phosphatidylinositol 4,5-bisphosphate through subsequent ______.

    <p>phosphorylations</p> Signup and view all the answers

    Match the following intermediates to their corresponding final products:

    <p>CDP - diacylglycerol = Phosphatidylserine CDP - ethanolamine = Phosphatidylethanolamine Phosphatidate = Phosphatidylinositol Phosphocholine = Phosphatidylcholine</p> Signup and view all the answers

    What three components are required for the desaturation of fatty acids in the microsomal system?

    <p>Molecular oxygen, NADH cytochrome-reductase, cytochrome-b, and desaturase</p> Signup and view all the answers

    Which enzyme catalyzes the conversion of glycerol-3-phosphate to lysophosphatidate?

    <p>Glycerophosphate acyl transferase</p> Signup and view all the answers

    Lysophosphatidate is formed by the reaction of glycerol-3-phosphate with two molecules of fatty acyl-CoA.

    <p>False</p> Signup and view all the answers

    Identify the type of messenger produced from the breakdown of phosphatidylinositol 4,5-bisphosphate.

    <p>Diacylglycerol and inositol triphosphate</p> Signup and view all the answers

    What is the initial molecule formed in the biosynthesis of sphingomyelin?

    <p>Ceramide</p> Signup and view all the answers

    Sphingomyelin is derived from glycerol rather than sphingosine.

    <p>False</p> Signup and view all the answers

    What is the role of S-adenosyl-methionine (SAM) in the biosynthesis of phosphatidylcholine?

    <p>It acts as a methyl donor.</p> Signup and view all the answers

    The enzyme that catalyzes the condensation of palmitoyl-CoA and serine to form 3-keto-sphinganine requires __________ for its function.

    <p>pyridoxal phosphate</p> Signup and view all the answers

    Match the following glycolipids with their characteristics:

    <p>Cerebroside = Linked to a sugar Sulfatide = Contains sulfate group Globoside = Contains multiple sugars Ganglioside = Contains sialic acid</p> Signup and view all the answers

    Which of the following correctly identifies a step in the synthesis of sphingomyelin?

    <p>Sphingosine + Acyl-CoA -&gt; Ceramide</p> Signup and view all the answers

    Cerebrosides are the most complex type of glycolipids.

    <p>False</p> Signup and view all the answers

    Name two types of glycolipids derived from ceramide.

    <p>Cerebrosides and gangliosides.</p> Signup and view all the answers

    Study Notes

    Lipid Metabolism (De Novo Synthesis of Fatty Acids)

    • Fatty acids are primarily obtained from diet, but synthesized when there's excess caloric intake.
    • Synthesis predominantly occurs in the liver and lactating mammary glands, with some in adipose tissue, kidneys, and brain.
    • De novo synthesis involves new reactions, not a simple reversal of degradation pathways.

    Fatty Acid Biosynthesis

    • Location: Cytosol
    • Intermediate Linking: Acyl carrier protein (ACP) sulfhydryl group.
    • Enzyme Arrangement: Multienzyme complex called fatty acid synthase.
    • Reducing Equivalents: NADPH
    • Carbon Addition: Two-carbon units (acetyl-CoA), sequentially added as malonyl-CoA to the growing fatty acid chain.
    • CO₂ Role: CO₂ participates in malonyl-CoA formation from acetyl-CoA.
    • Stereochemistry: Hydroxyl acyl group is D(-).
    • Primer: Acetyl-CoA contributes carbon atoms 15 and 16 of palmitate.
    • Subsequent Addition: All other 2-carbon units are added via malonyl-CoA.

    Fatty Acid Degradation

    • Location: Mitochondrial matrix
    • Intermediate Linking: Coenzyme A (CoA-SH).
    • Enzyme Association: Enzymes not usually associated.
    • Reducing Equivalents: NAD and FAD
    • Carbon Removal: Sequential removal of two-carbon units as acetyl-CoA.
    • CO₂ Involvement: No CO₂ participation.
    • Stereochemistry: Hydroxyl acyl group is L(-).

    Phases of De Novo Fatty Acid Synthesis

    • Phase 1: Transport of substrates into 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 various fatty acids including polyunsaturated fatty acids (PUFAs).

    Transport of Acetyl-CoA

    • Acetyl-CoA, produced in mitochondria, needs transport to the cytosol for fatty acid synthesis.
    • Citrate is used as a carrier, crossing the inner mitochondrial membrane, to carry acetyl-CoA to the cytosol.
    • Citrate is converted back to oxaloacetate and acetyl-CoA in the cytosol.
    • Oxaloacetate is transported back into the mitochondria.

    Carboxylation of Acetyl-CoA to Malonyl-CoA

    • Initial and rate-limiting reaction in fatty acid synthesis.
    • Catalyzed by acetyl-CoA carboxylase, utilizing biotin and bicarbonate.
    • Allosterically controlled, with citrate activating the enzyme and palmitoyl-CoA inhibiting it.

    Fatty Acid Synthase Complex

    • Multienzyme complex containing seven enzyme activities and an acyl carrier protein (ACP) segment.
    • Each monomer unit contains all seven reaction activities.
    • ACP acts as a carrier for the growing fatty acyl chain.

    Reactions in Phase II (Fatty Acid Synthase)

    • Transfer of acetyl group to cysteine-SH of 3-ketoacyl synthase.
    • Transfer of malonyl group to phosphopantetheine -SH of ACP.
    • Condensation to form acetoacetyl group bound to phosphopantetheine -SH.
    • Reduction, dehydration, and saturation.

    Fate of Palmitate

    • Activated to acyl CoA, it can be used as a precursor to longer chain fatty acids or be esterified into acylglycerols or cholesterol esters.

    Mitochondrial Elongation

    • Fatty acids can be elongated within mitochondria but occurs less frequently.
    • Acetyl-CoA serves as the source of 2-carbon units.

    Synthesis of Unsaturated Fatty Acids (Desaturation)

    • Microsomal enzymes introduce double bonds, requiring molecular oxygen and specific enzymes.
    • Mammals lack enzymes for introducing double bonds beyond the 9th carbon.

    Biosynthesis of Triacylglycerols

    • Fatty acids are activated to acyl CoA
    • Acyl-CoA and glycerol-3-phosphate combine to form phosphatidic acid and subsequently diacylglycerol.
    • Diacylglycerol reacts with acyl CoA to produce triacylglycerol.

    Fate of Triacylglycerol in Different Tissues

    • Liver: Little storage of triacylglycerol, predominantly export via Very Low Density Lipoproteins (VLDL).
    • Adipose tissue: Major storage site for triacylglycerol.

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    De Novo Synthesis of Fatty Acids (2016/2017) PDF

    Description

    This quiz explores key concepts in lipid biochemistry, focusing on the role of various lipids such as myelin, glycolipids, and phospholipids. Questions cover enzyme functions, lipid synthesis, and the metabolic pathways of triacylglycerols and glycerol in adipose tissue. Test your knowledge on lipoprotein lipase and hormone sensitive lipase activities.

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