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Medical Biochemistry > Ch. 17: Lipid II Phospholipids, Glycosphingolipids, Cholesterol > Flashcards

Ch. 17: Lipid II Phospholipids, Glycosphingolipids, Cholesterol Flashcards

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USMLE® Step 1 flashcards
1
Q

In what process do phospholipids & glycosphingolipids play an essential role?

What are their 2 other functions?

A

Synthesis of plasma lipoproteins & eicosanoids

Transduction of messages (cell surface receptors ➡️ 2nd messengers, control cell function)

Surfactants

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2
Q

Cholesterol: mainly plant or animal origin?

A

Animal origin

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3
Q

Cholesterol is an essential part of what structure?

A

Biomembranes (provides membrane fluidity)

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4
Q

In plasma, what is cholesterol associated with?

A

Lipoproteins

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5
Q

Cholesterol: precursor for what compounds?

A

Bile acids
Steroid hormones
7-dehydrocholesterol of vit D

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6
Q

What does esterifying cholesterol do to its properties?

A

Cholesterol esters: ⬆️ hydrophobic (pushed to center of lipoprotein)

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7
Q

What are the 2 types of phospholipase A2? Functions?

A

Cytosolic, soluble: housekeeping, no signals sent (not as powerful)

Membrane bound: receives signal ➡️ releases FAs

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8
Q

What are glycerolipids?

Types?

A

Phospholipid w/glycerol backbone

Phosphatidylcholine (lecithin)
Phosphatidylethanolamine (cephalin)
Phosphatidylserine
Phosphatidylinositol
Phosphatidylglycerol
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9
Q

What is cardiolipin? Importance?

A

Diphosphatidylglycerol

Only antigenic GPL, important part of inner MT membrane

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10
Q

What are sphingolipids?

A

Phospholipids with sphingosine

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11
Q

What is ceramide?

A

Sphingosine + LCFA attached to amino group of sphingosine

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12
Q

What is sphingomyelin? Importance?

A

Ceramide + phosphorylcholine

Important part of myelin of nerve fibers

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13
Q

Amino acids needed to synthesize choline?

A

Gly ➡️ Met ➡️ Choline

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14
Q

Steps in synthesis of phosphatidylcholine from choline?

A

Choline ➡️ phosphocholine (+ CTP nucleotide) ➡️ cytidine diphosphate-choline (CDP)

Glycerol ➡️ sn-G3P ➡️ lysophosphatidic acid ➡️ phosphatidic acid ➡️ sn-1,2-diacylglycerol (+ CDP) ➡️ phosphatidylcholine + CMP

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15
Q

What 2 products can be synthesized from choline?

A

Acetylcholine

Betaine ➡️ dimethylglycine (via methylation of homocysteine ➡️ met)

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16
Q

What is the main methyl donor in methylation of homocysteine ➡️ met? Importance?

What is the required cofactor in this reaction?

A

Methyl THF

Vitamin B12

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17
Q

What are the products from base exchange reaction between phosphatidylserine & ethanolamine?

What enzyme catalyzes this reaction?

A

Phosphatidylethanolamine & serine

Phosphatidylethanolamine-serine transferase

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18
Q

What enzyme directly converts phosphatidylserine ➡️ phosphatidylethanolamine?

A

Phosphatidylserine decarboxylase (loss of CO2)

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19
Q

How many SAM molecules are used to synthesize phosphatidylcholine?

What enzymes catalyze this reaction?

A

3 SAM ➡️ 3 SAH

N-methyltransferases

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20
Q

Compare phosphatidylethanolamine to platelet-activating factor: what are the differences in structure?

A

Platelet-activating factor:

1) acyl group on PE replaced with acetyl group via phospholipase A2
2) saturated bond (next to ether link) vs unsaturated bond in PE

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21
Q

Steps of synthesis of phosphatidylinositol from glycerol?

A

Glycerol ➡️ ➡️ phosphatidic acid ➡️ CDP-diacylglycerol ➡️ phosphatidylinositol

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22
Q

Steps of synthesis of cardiolipin (diphosphatidylglycerol) from glycerol?

A

Glycerol ➡️ ➡️ phosphatidic acid ➡️ CDP-diacylglycerol ➡️ phosphatidylglyceryl phosphate ➡️ phosphatidylglycerol ➡️ cardiolipin

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23
Q

Steps in the cleavage of phosphatidylinositol 4,5-bis P, with hormone as signal?

A

Hormone binds to receptor ➡️ receptor interacts w/Gs protein ➡️ GDP released, bind GTP ➡️ Gq alpha dissociates, ➕ phospholipase C ➡️ phosphatidylinositol 4,5-bisP cleaved to IP3 & diacylglycerol ➡️ IP3 binds to receptor on ER ➡️ Ca2+ released ➡️ Ca2+ & diacylglycerol ➕protein kinase C ➡️ phosphorylation of cellular proteins which mediate cellular response to hormone

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24
Q

What is sphingosine formed from? What is required for reaction?

A

Serine & palmitoyl-CoA

NADPH

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25
Q

What is ceramide formed from?

A

Sphingosine & 22C FA, oxidation of FAD

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26
Q

What are cerebrosides formed from?

A

Ceramide & UDP sugars

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27
Q

How are sulfides formed?

A

Addition of sulfate group to cerebroside

28
Q

How are gangliosides formed?

A

Addition of sugars to cerebroside

29
Q

What is fumonisin B1?

A

Toxin from fungi

disturbs spingolipid metabolism

30
Q

What is surfactant composed of?

A

90% lipids (lecithin 70-80%, PG 10%, PI, PE, PS,cholesterol)

5-10% surfactant specific proteins (SP-A, B, C, D)

31
Q

What are the general ratios of lipids in immature surfactant?

A

⬆️ PI, PE, PS

⬇️ lecithin

32
Q

What ratio of PG to PI indicates lung immaturity?

A

⬇️ PG to PI

33
Q

What disease is a consequence of prematurity and leading cause of neonatal mortality & morbidity?

What disease is associated w/sepsis, pneumonia, & injury to lungs due to trauma or surgery?

A

Respiratory distress syndrome

Acute respiratory distress syndrome

34
Q

What ratio in amniotic fluid indicates immaturity with ⬆️ likelihood of RDS?

A

⬇️ lecithin:sphingomyelin ratio (<1.5)

35
Q

Deficiency in what 2 things are immature infants susceptible to?

A

Surfactant

Antioxidant defense systems (important for when baby is breathing on its own ➡️ ⬆️O2)

36
Q

Storage disorders of sphingolipids: Tay-Sachs disease

Enzyme deficiency? Lipid accumulating? Clinical symptoms?

A

Hexosaminidase A

GM2 ganglioside

Mental retardation, blindness, cherry-red macula, muscle weakness, seizures

37
Q

Storage disorders of sphingolipids: Fabry’s disease

Enzyme deficiency? Lipid accumulating? Clinical symptoms?

A

Alpha-galactosidase

Globotriaosylceramide (globoside)

skin rash, kidney failure, heart failure, (X-linked recessive, full symptoms only in males)

38
Q

Storage disorders of sphingolipids: GM1 gangliosidosis

Enzyme deficiency? Lipid accumulating? Clinical symptoms?

A

Beta-galactosidase

Gangliosides (GM1), keratan sulfate

Hepatosplenomegaly, neurological deterioration, cherry-red macula, skeletal deformities

39
Q

Storage disorders of sphingolipids: Sandhoff’s disease

Enzyme deficiency? Lipid accumulating? Clinical symptoms?

A

Hexosaminidase A & B

Gangliosides (GM2), globosides

Same as Tay-Sachs, but also visceral involvement

40
Q

Storage disorders of sphingolipids: Metachromatic leukodystrophy

Enzyme deficiency? Lipid accumulating? Clinical symptoms?

A

Arylsulfatase A

3-sulfogalactosylceramide (Sulfatides)

Mental retardation & psychologic disturbances (adults), demyelination, nerves stain yellow-brown with cresylviolet

41
Q

Storage disorders of sphingolipids: Krabbe’s disease

Enzyme deficiency? Lipid accumulating? Clinical symptoms?

A

Beta-galactosidase

Galactosylceramide (galactocerebrosides)

Mental retardation, myelin almost absent, blindness, deafness, globoid bodies in white matter of brain

42
Q

Storage disorders of sphingolipids: Gaucher’s disease

Enzyme deficiency? Lipid accumulating? Clinical symptoms?

A

Beta-glucosidase

Glucosylceramide (glucocerebrosides)

Hepatosplenomegaly, erosion of long bones, mental retardation (infants), most common lysosomal storage disease

43
Q

Storage disorders of sphingolipids: Niemann-Pick disease

Enzyme deficiency? Lipid accumulating? Clinical symptoms?

A

Sphingomyelinase

Sphingomyelin

Hepatosplenomegaly, mental retardation, fatal in early life

44
Q

Storage disorders of sphingolipids: Farber’s disease

Enzyme deficiency? Lipid accumulating? Clinical symptoms?

A

Ceramidase

Ceramide

Hoarseness, dermatitis, skeletal deformation, joint deformity, mental retardation, fatal in early life

45
Q

All tissues in body synthesize cholesterol ➡️ which tissues make the most?

A

Liver
Intestine
Adrenal cortex
Reproductive tissues

46
Q

Where do the carbons in cholesterol come from? What provides the needed reducing equivalents?

A

Acetate

NADPH (from PPP)

47
Q

What are the 3 major sources of liver cholesterol?

A

Dietary cholesterol ➡️ chylomicron remnants

Cholesterol synthesized in extrahepatic tissues ➡️ HDL

De novo synthesis in liver

48
Q

What are the 3 main ways cholesterol leaves the liver? Which is the major of the 3?

A

Secretion of VLDL

Conversion to bile acids/salts

Free cholesterol secreted in bile (major)

49
Q

Steps in biosynthesis of mevalonate? Enzymes for each step?

A

2 acetyl CoA ➡️ acetoacetyl CoA (via thiolase)
Acetoacetyl CoA ➡️ HMG-CoA (via HMG-CoA synthase)
HMG-CoA ➡️ mevalonate (via HMG-CoA reductase)

50
Q

What drugs inhibit HMG CoA reductase?

What are the ➖ allosteric modulators of HMG-CoA?

A

Statins

➖: bile acid, cholesterol, mevalonate

51
Q

How does the liver use HMG-CoA in the MT? In the cytosol?

A

MT: ketogenesis

Cytosol: cholesterol synthesis

52
Q

Mevalonate ➡️ squalene ➡️ cholesterol

How many carbons for each?

A

Mevalonate: 6C
Squalene: 30C
Cholesterol: 27C

53
Q

What is the major control point for cholesterol biosynthesis? (Rate limiting step)

A

Reaction catalyzed by HMG-CoA reductase

54
Q

What are the 4 methods of regulation of cholesterol synthesis through HMG-CoA reductase?

A

1) sterol-dependent regulation of gene expression of HMG-CoA
2) sterol-independent phosphorylation/deP (inactive when phosphorylated)
3) hormonal regulation
4) inhibition by drugs: statins

55
Q

Which are the naturally occurring statins? Synthetic statins?

A

Natural: lovastatin, simvastatin, pravastatin

Synthetic: fluvastatin, atorvastatin, cerivastatin

56
Q

Bile acids in human bile:
45% is ?
31% is ?
24% is ?

A

45% chenodeoxycholyl-CoA (CDCA)
31% cholyl-CoA (CA)
24% deoxycholyl-CoA (DCA, secondary bile acid)

57
Q

2/3 of bile acid is derived from what?

A

HDL cholesterol delivered to liver

58
Q

What is rate-limiting step of bile acid synthesis?

What is required for this reaction?

A

Formation of 7alpha-hydroxy cholesterol via 7alpha-hydroxylase

NADPH, O2, cyt P-450

59
Q

What two amino acids are conjugated to bile acids?

A

Taurine

Glycine

60
Q

Microbial enzymes convert primary bile acids ➡️ secondary bile acids:

CA ➡️ ?
CDCA ➡️ ?

Which is reabsorbed/not reabsorbed?

A

CA ➡️ deoxycholic acid (reabsorbed)

CDCA ➡️ lithocholic acid (not reabsorbed, toxic)

61
Q

Where is majority of bile reabsorbed?

A

Ileum (90-95%)

5-10% excreted in feces

62
Q

Serum bile acid levels are a sensitive indicator for what?

A

Liver disease

63
Q

What occurs in hyperbile acidemia?

A

Pruritus
Steatorrhea
Hemolytic anemia
Further liver injury

64
Q

What is cholelithiasis?

A

Presence/formation of gallstones due to precipitation of cholesterol in bile

65
Q

What causes pigment stones to form?

A

⬆️ biliary (bile pigments/bilirubin glucuronides)

66
Q

If mole ratio of bile salts & PLs to cholesterol is < 10:1, what occurs?

A

Lithogenic (stone forming)

Medical Biochemistry (23 decks)

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