1. What chemical bond links fatty acids to glycerol in a triacylglycerol (triglyceride) molecule?
Correct Answer: C (Ester bond)
Triacylglycerols are formed when three fatty acid carboxyl groups (-COOH) condense with the three hydroxyl groups (-OH) of glycerol via ester linkages.
Triacylglycerols are formed when three fatty acid carboxyl groups (-COOH) condense with the three hydroxyl groups (-OH) of glycerol via ester linkages.
2. Which of the following is an essential polyunsaturated fatty acid (PUFA) in human nutrition?
Correct Answer: D (Linoleic acid)
Linoleic acid (omega-6) and alpha-linolenic acid (omega-3) cannot be synthesized by human desaturase enzymes and must be obtained from dietary sources.
Linoleic acid (omega-6) and alpha-linolenic acid (omega-3) cannot be synthesized by human desaturase enzymes and must be obtained from dietary sources.
3. Most naturally occurring unsaturated fatty acids in living organisms possess double bonds in which geometric conformation?
Correct Answer: A (Cis configuration)
Natural fatty acid double bonds almost exclusively exist in the *cis* conformation, which introduces a 30° kink into the hydrocarbon acyl chain.
Natural fatty acid double bonds almost exclusively exist in the *cis* conformation, which introduces a 30° kink into the hydrocarbon acyl chain.
4. How does increasing the number of double bonds affect the melting point of fatty acids?
Correct Answer: B (Decreases the melting point)
Double bonds introduce kinks that prevent tight packing and van der Waals stacking of hydrocarbon chains, drastically lowering the melting point.
Double bonds introduce kinks that prevent tight packing and van der Waals stacking of hydrocarbon chains, drastically lowering the melting point.
5. What is the primary storage form of neutral lipids in human adipose tissue?
Correct Answer: B (Triacylglycerols (Triglycerides))
Triacylglycerols are uncharged, anhydrous, highly reduced molecules that serve as the main long-term energy reserve in adipocytes.
Triacylglycerols are uncharged, anhydrous, highly reduced molecules that serve as the main long-term energy reserve in adipocytes.
6. Which term describes molecules like phospholipids that contain both a hydrophilic (polar) and a hydrophobic (nonpolar) region?
Correct Answer: A (Amphipathic)
Amphipathic (or amphiphilic) molecules contain distinct polar head groups and nonpolar tails, enabling them to assemble into lipid bilayers and micelles.
Amphipathic (or amphiphilic) molecules contain distinct polar head groups and nonpolar tails, enabling them to assemble into lipid bilayers and micelles.
7. What is the simplest phosphoglyceride that acts as the core precursor for the synthesis of all other glycerophospholipids?
Correct Answer: B (Phosphatidic acid (Diacylglycerol phosphate))
Phosphatidic acid consists of glycerol esterified to two fatty acids at C1 and C2 and a phosphate group at C3.
Phosphatidic acid consists of glycerol esterified to two fatty acids at C1 and C2 and a phosphate group at C3.
8. Lecithin is the common biochemical name for which phospholipid?
Correct Answer: A (Phosphatidylcholine)
Lecithin consists of phosphatidic acid attached to a choline head group; it is a major component of biological membranes and pulmonary surfactant.
Lecithin consists of phosphatidic acid attached to a choline head group; it is a major component of biological membranes and pulmonary surfactant.
9. Which specialized diphosphatidylglycerol phospholipid is found exclusively in the inner mitochondrial membrane and bacterial membranes?
Correct Answer: C (Cardiolipin)
Cardiolipin contains four fatty acyl chains and two phosphate groups; it is essential for the optimal functioning of respiratory electron transport chain complexes.
Cardiolipin contains four fatty acyl chains and two phosphate groups; it is essential for the optimal functioning of respiratory electron transport chain complexes.
10. Unlike glycerophospholipids, sphingolipids are built upon which 18-carbon amino alcohol backbone?
Correct Answer: A (Sphingosine)
Sphingolipids utilize sphingosine (or dihydrosphingosine) rather than glycerol as their structural foundation.
Sphingolipids utilize sphingosine (or dihydrosphingosine) rather than glycerol as their structural foundation.
11. A fatty acid linked to the amino group of sphingosine via an amide bond forms:
Correct Answer: A (Ceramide)
Ceramide is the fundamental parent structural unit for all complex sphingolipids (sphingomyelins, cerebrosides, and gangliosides).
Ceramide is the fundamental parent structural unit for all complex sphingolipids (sphingomyelins, cerebrosides, and gangliosides).
12. Sphingomyelin contains a ceramide backbone covalently attached to which polar head group?
Correct Answer: A (Phosphocholine or Phosphoethanolamine)
Sphingomyelin is the only membrane phospholipid that is not derived from glycerol; it is abundant in the myelin sheath surrounding nerve fibers.
Sphingomyelin is the only membrane phospholipid that is not derived from glycerol; it is abundant in the myelin sheath surrounding nerve fibers.
13. Which class of glycosphingolipids contains one or more sialic acid (N-acetylneuraminic acid / NANA) residues?
Correct Answer: C (Gangliosides)
Gangliosides are complex acidic glycosphingolipids with negatively charged sialic acid (NANA) moieties concentrated on neuron cell membranes.
Gangliosides are complex acidic glycosphingolipids with negatively charged sialic acid (NANA) moieties concentrated on neuron cell membranes.
14. Tay-Sachs disease is a fatal autosomal recessive lipid storage disorder caused by a deficiency of which lysosomal enzyme?
Correct Answer: A (Hexosaminidase A (accumulating GM2 ganglioside))
Hexosaminidase A deficiency blocks GM2 ganglioside breakdown, causing toxic accumulation in neurons and characteristic cherry-red macular spots.
Hexosaminidase A deficiency blocks GM2 ganglioside breakdown, causing toxic accumulation in neurons and characteristic cherry-red macular spots.
15. Niemann-Pick disease is characterized by lysosomal accumulation of sphingomyelin due to a genetic deficiency of:
Correct Answer: B (Sphingomyelinase)
Sphingomyelinase deficiency prevents sphingomyelin cleavage into ceramide and phosphocholine, leading to hepatosplenomegaly and neurodegeneration.
Sphingomyelinase deficiency prevents sphingomyelin cleavage into ceramide and phosphocholine, leading to hepatosplenomegaly and neurodegeneration.
16. The basic four-ring steroid nucleus found in cholesterol and bile acids is chemically known as:
Correct Answer: A (Cyclopentanoperhydrophenanthrene (Sterane))
The steroid skeleton comprises three fused six-membered cyclohexane rings (A, B, C) and one five-membered cyclopentane ring (D).
The steroid skeleton comprises three fused six-membered cyclohexane rings (A, B, C) and one five-membered cyclopentane ring (D).
17. How many carbon atoms are present in a molecule of cholesterol?
Correct Answer: C (27)
Cholesterol (C27H46O) has 27 carbon atoms, including an 8-carbon branched hydrocarbon tail attached at Carbon-17.
Cholesterol (C27H46O) has 27 carbon atoms, including an 8-carbon branched hydrocarbon tail attached at Carbon-17.
18. What is the rate-limiting, committed step enzyme in the de novo biosynthesis of cholesterol?
Correct Answer: A (HMG-CoA reductase)
3-Hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase converts HMG-CoA to mevalonate in the primary rate-limiting step of cholesterol synthesis.
3-Hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase converts HMG-CoA to mevalonate in the primary rate-limiting step of cholesterol synthesis.
19. Statin medications (e.g., Atorvastatin, Simvastatin) lower plasma cholesterol by which mechanism?
Correct Answer: A (Competitive inhibition of HMG-CoA reductase)
Statins are structural analogs of HMG-CoA that competitively inhibit HMG-CoA reductase, upregulating hepatic LDL receptors.
Statins are structural analogs of HMG-CoA that competitively inhibit HMG-CoA reductase, upregulating hepatic LDL receptors.
20. What is the initial, rate-limiting enzyme in the conversion of cholesterol to bile acids in hepatocytes?
Correct Answer: B (Cholesterol 7-alpha-hydroxylase (CYP7A1))
CYP7A1 introduces a hydroxyl group at C7 of cholesterol, representing the committed step in primary bile acid synthesis (cholic acid and chenodeoxycholic acid).
CYP7A1 introduces a hydroxyl group at C7 of cholesterol, representing the committed step in primary bile acid synthesis (cholic acid and chenodeoxycholic acid).
21. Which plasma lipoprotein class has the lowest density and the highest percentage of triacylglycerols?
Correct Answer: A (Chylomicrons)
Chylomicrons are large, triglyceride-rich lipoproteins (~85-90% triacylglycerols) synthesized in enterocytes to transport exogenous dietary lipids.
Chylomicrons are large, triglyceride-rich lipoproteins (~85-90% triacylglycerols) synthesized in enterocytes to transport exogenous dietary lipids.
22. Which lipoprotein is primarily responsible for transporting endogenous triglycerides from the liver to peripheral tissues?
Correct Answer: B (VLDL (Very Low-Density Lipoprotein))
VLDL is assembled and secreted by hepatocytes to transport endogenously synthesized triacylglycerols to peripheral tissues.
VLDL is assembled and secreted by hepatocytes to transport endogenously synthesized triacylglycerols to peripheral tissues.
23. Low-Density Lipoprotein (LDL) delivers cholesterol to peripheral cells by binding to the LDL receptor via which apolipoprotein?
Correct Answer: B (Apolipoprotein B-100)
ApoB-100 is the structural ligand on LDL particles recognized by cell-surface LDL receptors for receptor-mediated endocytosis.
ApoB-100 is the structural ligand on LDL particles recognized by cell-surface LDL receptors for receptor-mediated endocytosis.
24. High-Density Lipoprotein (HDL) mediates “reverse cholesterol transport” primarily with the help of which enzyme?
Correct Answer: A (LCAT (Lecithin-Cholesterol Acyltransferase))
Activated by ApoA-I on HDL, LCAT esterifies free cholesterol with fatty acids from phosphatidylcholine, trapping cholesterol esters inside the HDL core.
Activated by ApoA-I on HDL, LCAT esterifies free cholesterol with fatty acids from phosphatidylcholine, trapping cholesterol esters inside the HDL core.
25. Which apolipoprotein serves as an essential cofactor to activate Lipoprotein Lipase (LPL) on capillary endothelium?
Correct Answer: C (ApoC-II)
ApoC-II (acquired by chylomicrons and VLDL from HDL) activates endothelial lipoprotein lipase to hydrolyze core triacylglycerols into free fatty acids and glycerol.
ApoC-II (acquired by chylomicrons and VLDL from HDL) activates endothelial lipoprotein lipase to hydrolyze core triacylglycerols into free fatty acids and glycerol.
26. In analytical lipid chemistry, what does the “Saponification Number” measure?
Correct Answer: A (Average molecular weight / chain length of fatty acids (mg KOH per 1 g fat))
Saponification number is inversely proportional to the mean molecular weight of fatty acids in a fat sample.
Saponification number is inversely proportional to the mean molecular weight of fatty acids in a fat sample.
27. The “Iodine Number” of a fat or oil indicates its degree of:
Correct Answer: B (Unsaturation (number of carbon-carbon double bonds))
Iodine value represents the grams of iodine consumed by 100 grams of fat; higher values denote greater degrees of double-bond unsaturation.
Iodine value represents the grams of iodine consumed by 100 grams of fat; higher values denote greater degrees of double-bond unsaturation.
28. What does the “Acid Value” of a fat measure?
Correct Answer: A (Quantity of free fatty acids resulting from hydrolytic cleavage)
Acid value (mg KOH required to neutralize free fatty acids in 1 g fat) quantifies the extent of hydrolytic rancidity.
Acid value (mg KOH required to neutralize free fatty acids in 1 g fat) quantifies the extent of hydrolytic rancidity.
29. What end product of lipid peroxidation reacts with thiobarbituric acid (TBA test) to assess oxidative rancidity?
Correct Answer: B (Malondialdehyde (MDA))
Free radical attack on polyunsaturated fatty acids decomposes into dialdehydes like malondialdehyde, an established biomarker of oxidative damage.
Free radical attack on polyunsaturated fatty acids decomposes into dialdehydes like malondialdehyde, an established biomarker of oxidative damage.
30. In which subcellular compartment does mitochondrial beta-oxidation of fatty acids take place?
Correct Answer: C (Mitochondrial matrix)
Beta-oxidation enzymes are localized within the mitochondrial matrix to generate acetyl-CoA, NADH, and FADH2 directly adjacent to the respiratory chain.
Beta-oxidation enzymes are localized within the mitochondrial matrix to generate acetyl-CoA, NADH, and FADH2 directly adjacent to the respiratory chain.
31. What specialized carrier molecule translocates activated long-chain fatty acyl-CoA into the mitochondrial matrix?
Correct Answer: B (Carnitine)
The carnitine shuttle (via Carnitine Palmitoyltransferase I and II) transports long-chain fatty acids across the impermeable inner mitochondrial membrane.
The carnitine shuttle (via Carnitine Palmitoyltransferase I and II) transports long-chain fatty acids across the impermeable inner mitochondrial membrane.
32. Which enzyme of the carnitine shuttle is allosterically inhibited by Malonyl-CoA during fatty acid synthesis?
Correct Answer: A (Carnitine Palmitoyltransferase-I (CPT-I / CAT-I))
Malonyl-CoA inhibits CPT-I to prevent newly synthesized cytosolic fatty acids from immediately entering mitochondria for futile oxidation.
Malonyl-CoA inhibits CPT-I to prevent newly synthesized cytosolic fatty acids from immediately entering mitochondria for futile oxidation.
33. What is the net yield of ATP produced from the complete aerobic oxidation of one molecule of Palmitic acid (16:0)?
Correct Answer: C (106 ATP)
Palmitate yields 8 Acetyl-CoA, 7 FADH2, and 7 NADH (gross 108 ATP) minus 2 ATP equivalents consumed in initial fatty acid activation = 106 net ATP.
Palmitate yields 8 Acetyl-CoA, 7 FADH2, and 7 NADH (gross 108 ATP) minus 2 ATP equivalents consumed in initial fatty acid activation = 106 net ATP.
34. Beta-oxidation of odd-chain fatty acids terminates with which 3-carbon intermediate that enters the TCA cycle via Succinyl-CoA?
Correct Answer: B (Propionyl-CoA)
Propionyl-CoA is carboxylated (Biotin-dependent) to methylmalonyl-CoA and converted by a B12-dependent mutase into Succinyl-CoA.
Propionyl-CoA is carboxylated (Biotin-dependent) to methylmalonyl-CoA and converted by a B12-dependent mutase into Succinyl-CoA.
35. In which organ does ketogenesis (synthesis of acetoacetate, beta-hydroxybutyrate, and acetone) exclusively occur?
Correct Answer: B (Liver)
Hepatocyte mitochondrial matrix produces ketone bodies during prolonged fasting, starvation, or uncontrolled diabetes due to high beta-oxidation rates.
Hepatocyte mitochondrial matrix produces ketone bodies during prolonged fasting, starvation, or uncontrolled diabetes due to high beta-oxidation rates.
36. Why is the liver unable to utilize ketone bodies as fuel for its own energy needs?
Correct Answer: A (It lacks the enzyme beta-ketoacyl-CoA transferase (Thiophorase))
Without thiophorase (succinyl-CoA:3-ketoacid CoA transferase), the liver cannot reactivate acetoacetate to acetoacetyl-CoA, ensuring ketone delivery to extrahepatic tissues.
Without thiophorase (succinyl-CoA:3-ketoacid CoA transferase), the liver cannot reactivate acetoacetate to acetoacetyl-CoA, ensuring ketone delivery to extrahepatic tissues.
37. In which cellular compartment does de novo fatty acid synthesis take place?
Correct Answer: A (Cytosol)
Fatty acid synthesis occurs in the cytoplasm utilizing NADPH and acetyl-CoA exported from mitochondria via the citrate shuttle.
Fatty acid synthesis occurs in the cytoplasm utilizing NADPH and acetyl-CoA exported from mitochondria via the citrate shuttle.
38. What is the rate-limiting enzyme of fatty acid synthesis that converts Acetyl-CoA to Malonyl-CoA?
Correct Answer: B (Acetyl-CoA Carboxylase (ACC))
ACC requires Biotin, ATP, and CO2; it is activated allosterically by Citrate and inhibited by Palmitoyl-CoA.
ACC requires Biotin, ATP, and CO2; it is activated allosterically by Citrate and inhibited by Palmitoyl-CoA.
39. Which prosthetic group is attached to the Acyl Carrier Protein (ACP) domain of the Fatty Acid Synthase (FAS) complex?
Correct Answer: B (4′-Phosphopantetheine)
4′-Phosphopantetheine (derived from pantothenic acid / Vitamin B5) acts as a flexible arm carrying growing acyl intermediates between catalytic domains of FAS.
4′-Phosphopantetheine (derived from pantothenic acid / Vitamin B5) acts as a flexible arm carrying growing acyl intermediates between catalytic domains of FAS.
40. What is the 20-carbon polyunsaturated fatty acid that serves as the immediate precursor for prostaglandins, prostacyclins, and thromboxanes?
Correct Answer: C (Arachidonic acid (20:4 delta 5,8,11,14))
Arachidonic acid is cleaved from membrane phospholipids by Phospholipase A2 and converted into eicosanoids via cyclooxygenase (COX) or lipoxygenase (LOX) pathways.
Arachidonic acid is cleaved from membrane phospholipids by Phospholipase A2 and converted into eicosanoids via cyclooxygenase (COX) or lipoxygenase (LOX) pathways.
41. Aspirin reduces inflammation, fever, and pain by irreversible covalent acetylation and inhibition of:
Correct Answer: A (Cyclooxygenase (COX-1 and COX-2))
Aspirin transfers an acetyl group to a key serine residue in the active site of COX enzymes, permanently blocking prostaglandin and thromboxane synthesis.
Aspirin transfers an acetyl group to a key serine residue in the active site of COX enzymes, permanently blocking prostaglandin and thromboxane synthesis.
42. Which hormone activates Hormone-Sensitive Lipase (HSL) in adipose tissue to initiate lipolysis during fasting or exercise?
Correct Answer: B (Epinephrine and Glucagon)
Epinephrine and glucagon bind G-protein-coupled receptors, raising cAMP and activating Protein Kinase A (PKA), which phosphorylates and activates HSL.
Epinephrine and glucagon bind G-protein-coupled receptors, raising cAMP and activating Protein Kinase A (PKA), which phosphorylates and activates HSL.
43. Which lipolytic hormone strongly suppresses lipolysis and promotes triglyceride storage in adipocytes?
Correct Answer: A (Insulin)
Insulin activates protein phosphatase and phosphodiesterase (PDE3B) to dephosphorylate and inactivate Hormone-Sensitive Lipase.
Insulin activates protein phosphatase and phosphodiesterase (PDE3B) to dephosphorylate and inactivate Hormone-Sensitive Lipase.
44. In pulmonary surfactant, what specific phospholipid prevents alveolar collapse during expiration by reducing surface tension?
Correct Answer: A (Dipalmitoylphosphatidylcholine (DPPC))
DPPC is the primary active surfactant component produced by type II alveolar pneumocytes; deficiency leads to neonatal Respiratory Distress Syndrome (RDS).
DPPC is the primary active surfactant component produced by type II alveolar pneumocytes; deficiency leads to neonatal Respiratory Distress Syndrome (RDS).
45. What histological dye is commonly used to stain neutral lipid droplets bright red/orange in laboratory tissue sections?
Correct Answer: C (Oil Red O (or Sudan IV))
Sudan dyes and Oil Red O are fat-soluble lysochrome dyes that partition preferentially into hydrophobic lipid vacuoles.
Sudan dyes and Oil Red O are fat-soluble lysochrome dyes that partition preferentially into hydrophobic lipid vacuoles.
46. What uncoupling protein in brown adipose tissue generates heat by dissipating the mitochondrial proton gradient?
Correct Answer: A (Thermogenin (UCP-1))
UCP-1 allows protons to re-enter the mitochondrial matrix without generating ATP, converting metabolic energy into heat (non-shivering thermogenesis).
UCP-1 allows protons to re-enter the mitochondrial matrix without generating ATP, converting metabolic energy into heat (non-shivering thermogenesis).
47. Which lipid class consists of long-chain fatty acids esterified to long-chain aliphatic monohydroxy alcohols?
Correct Answer: C (Waxes)
Waxes (e.g., beeswax, spermaceti, cutin) are high-melting esters of high-molecular-weight fatty acids with long-chain fatty alcohols.
Waxes (e.g., beeswax, spermaceti, cutin) are high-melting esters of high-molecular-weight fatty acids with long-chain fatty alcohols.
48. Phospholipase C cleaves phosphatidylinositol 4,5-bisphosphate (PIP2) to produce which two intracellular second messengers?
Correct Answer: A (Inositol 1,4,5-trisphosphate (IP3) and Diacylglycerol (DAG))
IP3 diffuses to release calcium from the endoplasmic reticulum, while membrane-bound DAG activates Protein Kinase C (PKC).
IP3 diffuses to release calcium from the endoplasmic reticulum, while membrane-bound DAG activates Protein Kinase C (PKC).
49. What is the physiological purpose of Zellweger syndrome patients lacking functional peroxisomes in relation to lipid metabolism?
Correct Answer: B (Inability to oxidize very-long-chain fatty acids (VLCFA, ≥C24))
Peroxisomes initiate beta- and alpha-oxidation of very long-chain and branched fatty acids (like phytanic acid); peroxisome biogenesis failure causes toxic VLCFA accumulation.
Peroxisomes initiate beta- and alpha-oxidation of very long-chain and branched fatty acids (like phytanic acid); peroxisome biogenesis failure causes toxic VLCFA accumulation.
50. Which analytical parameter evaluates the amount of volatile, water-soluble fatty acids in butter and fat products?
Correct Answer: C (Reichert-Meissl (RM) number)
The RM value measures the number of mL of 0.1 N KOH required to neutralize steam-volatile water-soluble fatty acids (such as butyric and caproic acids) extracted from 5 g of fat.
The RM value measures the number of mL of 0.1 N KOH required to neutralize steam-volatile water-soluble fatty acids (such as butyric and caproic acids) extracted from 5 g of fat.