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Lipid Structure and Function - I Flashcards

1
Q

What are lipids?

A

Lipids are insoluble in water and include fats, oils, phospholipids, and sterols. They serve as energy stores, structural components of membranes, enzyme cofactors, and signaling molecules.

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2
Q

How do saturated and unsaturated fatty acids differ?

A

Saturated fatty acids have no double bonds (higher melting points), while unsaturated fatty acids have one or more double bonds (lower melting points).

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2
Q

What is the difference between saponifiable and nonsaponifiable lipids?

A

Saponifiable lipids yield fatty acid salts upon alkaline hydrolysis (e.g., acylglycerols, waxes). Nonsaponifiable lipids resist hydrolysis (e.g., steroids, terpenes).

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2
Q

Name three types of simple lipids.

A

Fats, oils, and waxes (esters of fatty acids with glycerol or alcohols).

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2
Q

What is the impact of trans fats on health?

A

Trans fats raise LDL (“bad” cholesterol), lower HDL (“good” cholesterol), and increase cardiovascular disease risk.

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3
Q

What are the two main classes of lipids?

A

Polar (amphipathic, e.g., phospholipids, sphingolipids) and non-polar (e.g., triacylglycerols, cholesteryl esters).

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4
Q

Name two essential polyunsaturated fatty acids.

A

Linoleic acid (18:2) and α-linolenic acid (18:3).

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5
Q

What are the major phospholipids in cell membranes?

A

Phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylserine (PS).

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6
Q

Why is dipalmitoyllecithin important?

A

It is a lung surfactant; its deficiency causes respiratory distress syndrome in premature infants.

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7
Q

What is the role of phosphatidylinositol?

A

Signal transduction and source of arachidonic acid for prostaglandin synthesis.

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8
Q

Compare LDL and HDL.

A

LDL delivers cholesterol to peripheral tissues (“lethal”), while HDL mediates reverse cholesterol transport to the liver (“healthy”).

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9
Q

Which apolipoprotein activates LCAT?

A

ApoA-I (found in HDL).

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10
Q

What is the function of ApoC-II?

A

It acts as a cofactor for lipoprotein lipase, cleaving triglycerides in chylomicrons and VLDL.

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11
Q

What are glycolipids? Give an example.

A

Lipids with carbohydrate groups (e.g., cerebrosides, gangliosides). GM1 ganglioside is a receptor for cholera toxin.

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12
Q

What is the biological role of ether lipids like PAF?

A

Platelet-activating factor (PAF) mediates inflammation, allergies, and anaphylactic shock.

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13
Q

Name a steroid hormone precursor.

A

7-Dehydrocholesterol (precursor of vitamin D).

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14
Q

Why are terpenes significant?

A

They include squalene (cholesterol precursor) and fat-soluble vitamins (A, D, E, K).

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14
Q

What determines ABO blood group antigens?

A

Glycosphingolipids with specific terminal sugars (e.g., N-acetylgalactosamine for type A).

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15
Q

How do waxes differ from triacylglycerols?

A

Waxes are esters of fatty acids with long-chain alcohols, solid at room temperature, and water-repellent.

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16
Q

How are fatty acids named systematically?

A

By carbon count, double bonds (Δⁿ), and cis/trans configuration, e.g., cis-9-octadecenoic acid (oleic acid).

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17
Q

What does the sn- prefix indicate in phospholipids?

A

sn- (stereospecific numbering) denotes the stereochemistry of glycerol derivatives, e.g., sn-glycerol-3-phosphate.

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18
Q

Why are plasmalogens critical in myelin?

A

Ethanolamine plasmalogens stabilize myelin membranes and protect against oxidative stress.

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19
Q

How is fetal lung maturity assessed prenatally?

A

Via the lecithin/sphingomyelin (L/S) ratio in amniotic fluid; low ratios indicate risk for respiratory distress syndrome.

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20
Q

What is the role of sulfolipids?

A

Found in plant chloroplasts, they participate in photosynthesis and membrane structure.

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21
Which apolipoprotein mediates remnant uptake by the liver?
ApoE (present on chylomicron remnants, VLDL, IDL, and HDL).
21
Which lipoprotein has the highest triglyceride content?
Chylomicrons (84–89% TG).
22
What is unique about ApoB-48 vs. ApoB-100?
ApoB-48 (intestinal) lacks LDL-receptor binding domain; ApoB-100 (hepatic) binds LDL receptors.
23
How does Trypanosoma brucei evade host immunity?
It sheds GPI-anchored surface glycoproteins via C-type phospholipase, escaping antibodies.
23
What toxin exploits ganglioside GM1?
Cholera toxin binds GM1 on intestinal cells, triggering fluid loss.
24
What is the structure of platelet-activating factor (PAF)?
Ether-linked alkyl chain at sn-1, acetyl group at sn-2, and choline at sn-3.
25
How is PAF released?
Synthesized de novo by stimulated polymorphonuclear neutrophils (PMNs) during inflammation.
26
Why do unsaturated fatty acids have lower melting points?
Cis double bonds introduce kinks, reducing packing efficiency and intermolecular forces.
27
What is the pKa range of fatty acids?
4–5; they exist as carboxylate anions (soaps) at physiological pH.
28
Why is phosphatidylserine (PS) acidic?
It carries a net −1 charge at pH 7 due to its serine head group.
29
Where is cardiolipin found?
Inner mitochondrial membrane; it has −2 charge and stabilizes electron transport chain proteins.
30
What distinguishes blood group A from B antigens?
A: Terminal N-acetylgalactosamine; B: Terminal galactose. Both share a core oligosaccharide.
31
What is the function of globosides?
Glycosphingolipids involved in cell recognition (e.g., ABO antigens) and tissue compatibility.
32
Which vitamin is derived from 7-dehydrocholesterol?
Vitamin D₃ (cholecalciferol), synthesized in skin via UV exposure.
33
Name two isoprenoid vitamins.
Vitamin E (antioxidant), Vitamin K (cofactor for blood clotting).
34
What is the major phospholipid in HDL₂?
Phosphatidylcholine (35% of HDL₂ lipid content).
35
How is palmitoleic acid systematically named?
16:1 cisΔ⁹ (16 carbons, 1 double bond at C9–10, cis configuration).
36
What distinguishes α-linolenic acid (18:3) from arachidonic acid (20:4)?
α-Linolenic: 18 carbons, 3 double bonds (Δ⁹,¹²,¹⁵); Arachidonic: 20 carbons, 4 double bonds (Δ⁵,⁸,¹¹,¹⁴).
37
What is the omega (ω) classification of eicosapentaenoic acid (EPA)?
ω-3 fatty acid (last double bond at 3rd carbon from methyl end).
38
How does aspirin affect prostaglandin synthesis?
Inhibits prostaglandin synthase (cyclooxygenase), blocking inflammation.
39
Compare prostaglandins and thromboxanes.
Prostaglandins: Short-lived, act on muscles (uterine/intestinal), synthesized in most cells. Thromboxanes: Promote clot formation, made in platelets/lungs.
40
What is the role of leukotriene C₄?
Mediates allergic reactions (e.g., asthma) via smooth muscle contraction.
41
Why is linoleic acid (18:2) essential in the diet?
Humans cannot synthesize ω-6 fatty acids; deficiency causes skin lesions and growth impairment.
42
Which lipid derivative acts as a local hormone?
Prostaglandins (e.g., regulate inflammation, blood flow).
43
What is the consequence of sphingolipid accumulation in lysosomes?
Causes lysosomal storage diseases (e.g., Tay-Sachs, Gaucher’s disease).
43
What is the general structure of lipoproteins?
Core: TGs/cholesteryl esters; Shell: Amphipathic lipids (phospholipids, unesterified cholesterol) and apoproteins.
44
Which phospholipid is critical for lung surfactant?
Dipalmitoylphosphatidylcholine (DPPC) prevents alveolar collapse.
45
How do gangliosides participate in cell signaling?
Contain sialic acids (e.g., GM1 binds cholera toxin).
45
What is the function of dolichols?
Lipid carriers for protein glycosylation in the ER.
46
Which lipid acts as a second messenger in signaling?
Phosphatidylinositol 4,5-bisphosphate (PIP₂) generates IP₃/DAG.
47
What is the primary source of arachidonic acid for eicosanoid synthesis?
Membrane phospholipids (cleaved by phospholipase A₂).
48
What molecules are required to synthesize ceramide?
Palmitoyl-CoA, serine, and fatty acyl-CoA.
49
Which enzyme pathway produces leukotrienes?
Lipoxygenase pathway (vs. cyclooxygenase for prostaglandins).
50
What vitamin is derived from 7-dehydrocholesterol?
Vitamin D₃ (activated by UV light).
51
Which lipoprotein component is NOT part of the outer shell?
Triacylglycerols (they are in the core).
52
What does 18:3 cisΔ⁹,¹²,¹⁵ represent?
α-Linolenic acid (not linoleic or arachidonic).
53
Which molecule is NOT found in gangliosides?
Phosphate (they contain ceramide, sugars, and sialic acids).
54
Why is arachidonic acid (20:4) clinically significant?
Precursor for eicosanoids (prostaglandins, thromboxanes, leukotrienes) that regulate inflammation, blood clotting, and immunity.
55
What structural feature distinguishes omega-3 from omega-6 fatty acids?
Position of the last double bond: ω-3 (3rd carbon from methyl end), ω-6 (6th carbon). Example: EPA (ω-3) vs. linoleic acid (ω-6).
56
How do NSAIDs (e.g., ibuprofen) differ from aspirin in action?
Both inhibit cyclooxygenase (COX), but aspirin irreversibly acetylates COX, while NSAIDs reversibly block it.
57
Which eicosanoid promotes vasodilation and inhibits platelet aggregation?
Prostacyclin (PGI₂) (contrasts with thromboxane A₂, which promotes clotting).
58
What disease is linked to leukotriene overproduction?
Asthma (LTB₄ recruits inflammatory cells; LTC₄/LTD₄ cause bronchoconstriction).
59
How does phosphatidylinositol 4,5-bisphosphate (PIP₂) function in signaling?
Cleaved by phospholipase C into IP₃ (releases Ca²⁺) and DAG (activates PKC).
59
What is the role of sphingosine-1-phosphate (S1P)?
Regulates immune cell trafficking, endothelial barrier function, and heart rate (target of drug fingolimod for multiple sclerosis).
60
Why might a fat-free diet cause essential fatty acid deficiency?
Lack of linoleic acid (ω-6) and α-linolenic acid (ω-3), which humans cannot synthesize. Symptoms: dermatitis, poor wound healing.
61
How does cholera toxin exploit ganglioside GM1?
Binds GM1 on intestinal cells → overactivates adenylate cyclase → cAMP surge → severe fluid loss (diarrhea).
62
What lipid accumulates in Niemann-Pick disease?
Sphingomyelin due to deficient sphingomyelinase (lysosomal storage disorder).
63
Why do cis double bonds lower lipid melting points?
Introduce kinks → disrupts tight packing → weaker van der Waals forces.
64
What distinguishes plasmalogens from other phospholipids?
Ether-linked alk-1-enyl chain at sn-1 (vs. ester-linked fatty acid). Abundant in brain/heart.5
65
How is platelet-activating factor (PAF) unique structurally?
Ether-linked alkyl chain at sn-1 + acetyl group at sn-2 (vs. long acyl chain).
66
Why does HDL have a higher protein content than chylomicrons?
HDL is dense (protein-rich) to shuttle cholesterol from tissues to liver (reverse transport).
67
What apolipoprotein deficiency causes Type III hyperlipoproteinemia?
ApoE defect → impaired remnant clearance (elevated chylomicrons/VLDL remnants).
68
What enzyme converts arachidonic acid to prostaglandin H₂ (PGH₂)?
Cyclooxygenase (COX-1/COX-2).
69
How is ceramide synthesized?
Palmitoyl-CoA + serine → sphinganine → ceramide (add fatty acyl-CoA).
70
What breaks down sphingomyelin in lysosomes?
Sphingomyelinase (deficient in Niemann-Pick disease).
71
How do statins indirectly affect lipid signaling?
Lower cholesterol → reduces LDL → decreases oxidative stress/inflammation.
72
73
What is the Lecithin/Sphingomyelin (L/S) ratio diagnostic for?
Fetal lung maturity (L/S ≥2 indicates sufficient surfactant).
73
What is the GPI anchor’s role in Trypanosoma brucei?
Allows antigenic variation by shedding surface glycoproteins to evade immunity.
74
Which lipid acts as a vitamin D precursor?
7-Dehydrocholesterol (converted to cholecalciferol via UV light).

AI Questions (232) (22 decks)

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