Deck 18: Lipid Metabolism II: Pathways of Metabolism of Special Lipids

Question 1

The products of the hydrolysis of sphingomyelin by sphingomyelinase, a phospholipase C - like enzyme, are

A) acylceramide and phosphate.
B) ceramide and phosphorylcholine
C) ceramide, choline, and phosphate.
D) ceramide, a fatty acid, and choline.
E) ceramide phosphate and choline.

Answer 1

ceramide and phosphorylcholine

Question 2

Which of the following is the most correct sequence involved in the synthesis of triacylglycerols (triglycerides) in the fat cell?

A) glycerol 3-phosphate ==> PA ==> 1,2-DG ==> TG
B) PA ==> glycerol 3-phosphate ==> 1,2-DG ==> TG
C) glycerol 3-phosphate ==> MG ==> DG ==> TG
D) glycerol 3-phosphate ==> 1,2-DG ==> PA ==> TG
E) glycerol ==> glycerol 3-phosphate ==> PA == 1,2-DG ==> TG

Answer 2

glycerol 3-phosphate ==> PA ==> 1,2-DG ==> TG

Question 3

Which of the following statements concerning the serum lipoproteins is true?

A) The chylomicron particle is smaller than the LDL particle.
B) The density of a lipoprotein increases as the ratio of lipid to protein in the particle increases.
C) Most of the triglyceride in serum is contained in VLDL and chylomicrons.
D) Most of the cholesterol in serum is contained in LDL as unesterified cholesterol.
E) none of the above.

Answer 3

Most of the triglyceride in serum is contained in VLDL and chylomicrons.

Question 4

Niemann Pick disease results from a deficiency of

A) lipoprotein lipase.
B) sphingomyelinase.
C) adipolytic lipase.
D) pancreatic lipase.
E) none of the above.

Question 5

Geranyl pyrophosphate condenses with isopentenyl pyrophosphate to form

A) 3,3-dimethylallyl pyrophosphate.
B) presqualene pyrophosphate.
C) squalene.
D) farnesyl pyrophosphate.
E) none of the above possibilities.

Question 6

Which of the following statements about the synthesis of phospholipids is TRUE?

A) phosphatidyl ethanolamine is methylated to phosphatidyl choline by S-adenosyl methionine.
B) Free unesterified choline reacts with a diglyceride to form phosphatidyl choline.
C) phosphatidyl alanine is hydroxylated to form phosphatidyl serine.
D) Fatty acids are added to phospholipids as CDP-fatty acids.

Question 7

Which group of molecules appropriately combined would form lecithin?

A) glucose, N-acetylgalactosamine, glycerol, phosphoric acid, two fatty acids
B) phosphoric acid, glycerol, two fatty acids, choline
C) phosphoric acid, sphingosine, fatty acid, glucose, N-acetylneuraminic acid, N-acetylgalactosamine
D) choline, phosphoric acid, sphingosine, fatty acid
E) glycerol, two fatty acids, phosphoric acid, ethanolamine

Question 8

Cholesterol serves as a precursor for each of the following EXCEPT

A) prostacyclin.
B) pregnenolone.
C) glycocholate.
D) cholecalciferol (Vitamin D3)

Question 9

In the metabolism of cholesterol in the human

A) cholesterol conversion to bile salts involves shortening of the side chain of cholesterol.
B) plasma cholesterol readily exchanges with the brain cholesterol.
C) plasma cholesterol is entirely in the form of cholesterol esters.
D) cholesterol can be oxidized to carbon dioxide and water.
E) cholesterol is synthesized only in the liver.

Question 10

Very low density serum lipoproteins transport

A) non-esterified fatty acids to the liver.
B) medium chain non-esterified fatty acids via the lymphatic system.
C) non-esterified fatty acids to the adipose tissues.
D) triacylglycerol from the liver to the adipose tissues.
E) none of these.

Question 11

A pharmacological dose of a non-steroidal anti-inflammatory agent would not inhibit the synthesis of

A) thromboxanes.
B) prostacyclins.
C) leukotrienes.
D) E-series prostaglandins.
E) F-series prostaglandins.

Question 12

In the cell, squalene

A) is a hydrocarbon that may undergo attack by oxygen to form an epoxide.
B) is a complex fatty acid which accumulates in Refsum's disease.
C) is a steroid which is a cholesterol precursor.
D) is a product of cholesterol catabolism.
E) is found only in sharks of the genus Squalus.

Question 13

In the synthesis of cholesterol

A) only the methyl group of acetyl CoA is incorporated.
B) most of the reactions take place in the mitochondria.
C) dietary cholesterol has no influence on the rate.
D) mevalonic acid formation seems to be the controlling step.
E) the adrenal gland is the only tissue which is active.

Question 14

Phosphatidate phosphatase is involved in the synthetic pathway for

A) choline.
B) glycerol phosphate.
C) phosphatidic acid.
D) cholesterol.
E) triglycerides.

Question 15

The uptake of LDL into a cell by the LDL receptor does all of the following EXCEPT

A) stimulates cellular acyl-CoA:cholesterol acyltransferase (ACAT).
B) inhibits hydroxymethylglutaryl-CoA (HMG-CoA) reductase.
C) decreases the rate of synthesis of the LDL receptor.
D) increases cholesterol esterification.
E) converts LDL to HDL and HDL remnants.

Question 16

All of the following are true about a ceramide EXCEPT which one?

A) It has two nonpolar tails.
B) The sphingosine base is attached via an amide linkage to a saturated or mono-unsaturated fatty acid.
C) The different polar head groups are attached to the hydroxyl group (position 1)of the sphingosine base.
D) They are found in highest concentration in depot fat.

Question 17

All of the following statements on the biosynthesis of phosphatidylcholine (lecithin) in mammalian adipose tissue are correct EXCEPT which one?

A) CTP is required
B) S-adenosylmethionine is required
C) The non-phosphorylated form of glycerol phosphate acyl transferase is required
D) Absence of 3',5'-cyclic AMP is inhibitory
E) phosphatidate phosphohydrolase is required

Question 18

A characteristic feature common to the degradation of most sphingolipids, including gangliosides, is

A) catalysis by lysosomal enzymes.
B) catalysis by peroxisomal enzymes.
C) feedback regulation by ceramide.
D) hormonal regulation by glucocorticoids.
E) participation of nucleotide intermediates.

Question 19

Both aspirin and indomethacin block prostaglandin formation by inhibition of

A) cyclooxygenase
B) diacylglycerol lipase.
C) 5-lipooxygenase.
D) phospholipase A2.
E) phospholipase C

Question 20

Lipoprotein lipase is

A) an intracellular enzyme.
B) stimulated by cAMP.
C) stimulated by epinephrine.
D) stimulated by one of the apolipoproteins found in VLDL.
E) the stimulus for mobilization of stored triglycerides from adipose tissue.

Question 21

CDP-diglyceride is an intermediate in the de novo synthesis of

A) phosphatidylserine.
B) phosphatidylcholine.
C) phosphatidylethanolamine.
D) Triglycerides.
E) None of the above.

Question 22

The second step of prostaglandin synthase converts PGG₂ to PGH₂. What is the cofactor for this reaction?

A) Biopterin
B) FADH₂
C) Glutathione
D) NADH
E) Pyridoxal phosphate

Question 23

The initial catalytic steps in the synthesis of cholesterol from acetyl-CoA are utilized by the pathway producing

A) acetoacetate.
B) ceramide.
C) citrate.
D) palmitate.
E) ribulose 5?phosphate.

Question 24

In the synthesis of prostaglandins and thromboxanes

A) arachidonic acid of the cytosol serves as the primary precursor.
B) PG synthase uses 2 molecules of oxygen to generate the endoperoxide PGG₂.
C) PGE₂ synthesis would be inhibited by aspirin but thromboxane synthesis would not be affected.
D) PGH₂ is the precursor of PGE₂ but PGI₂ is the precursor of TXA₂.
E) all tissues have the capacity to synthesize all of the prostaglandins.

Question 25

A precursor of leukotrienes.

A) inositol 1,4,5 trisphosphate
B) diacylglycerol
C) cholera toxin
D) arachidonic acid
E) cAMP

Question 26

The rate-limiting step in the conversion of cholesterol to bile acids is

A) side chain oxidation.
B) 12-alpha-hydroxylation.
C) 7-alpha-hydroxylation.
D) 7-beta-hydroxylation.
E) conversion to coprostanol.

Question 27

Prostaglandins are inactivated

A) primarily in the liver.
B) in the presence of molecular oxygen.
C) only in the circulation.
D) by oxidation of the 15 hydroxy group by a prostaglandin dehydrogenase.
E) by conversion to thromboxanes.

Question 28

Phosphatidylcholine is synthesized by the reaction of

A) phosphatidic acid and CDP-choline.
B) 1-palmitoyl-sn-glycerol-3-phosphate and CDP-choline.
C) 1-palmitoyl-sn-glycerol and CDP-choline.
D) lysolecithin and CDP-choline.
E) diacylglycerol and CDP-choline.

Question 29

The enzyme that condenses serine and palmitoyl-CoA to form -dehydrosphinganine requires

A) retinal.
B) pyridoxal phosphate.
C) niacin.
D) vitamin B₁₂.
E) biotin.

Question 30

Chylomicrons:

A) mainly carry dietary triglycerides.
B) require the action of LDL for absorption.
C) are secreted into the blood directly from the intestine.
D) are smaller than HDL.
E) have more phospholipid than HDL.

Question 31

A ceramide is composed of

A) sphingosine and fatty acid.
B) sphingosine and glucose.
C) sphingosine and serine.
D) glycerol and fatty acid.
E) glycerol and choline.

Question 32

Loss of hexosaminidase A activity results in accumulation of

A) galactocerebroside.
B) glucocerebroside.
C) G-ganglioside.
D) sphingomyelin.
E) sulfatide

Question 33

phosphatidylcholine participates in the synthesis of sphingomyelin by providing

A) an acylglycerol group.
B) a ceramide group.
C) a fatty acyl group.
D) a phosphorylcholine group.

Question 34

Which of the following is directly involved in the biosynthesis of sphingosine?

A) squalene
B) spermine
C) serotonin
D) serine
E) sorbitol

Question 35

Changes in the extent of phosphorylation of 3-hydroxy-3-methyl glutaryl-CoA reductase

A) are induced by reabsorbed bile acids.
B) are regulated by the level of dietary cholesterol.
C) control the rate of synthesis of cholesterol.
D) represent a type of co-translational modification of the protein.

Question 36

Which of the following serum lipoproteins possesses the highest concentration of protein (mg protein/g lipoprotein)?

A) chylomicrons
B) VLDL
C) IDL
D) LDL
E) HDL

Question 37

An established function of one of the apolipoproteins in the LDL particle is to

A) activate lecithin-cholesterol acyl transferase.
B) coat pits in the plasma membrane with its cage-like structure.
C) hydrolyze cholesterol esters in preparation for receptor-mediated endocytosis.
D) provide a recognition marker for binding to the LDL receptor.
E) disrupt the gel network preventing lysosomal budding.

Question 38

All the following statements regarding ethanolamine are correct EXCEPT

A) For the formation of phosphatidyl ethanolamine, ethanolamine needs to be activated by ATP and CTP.
B) Ethanolamine can be produced from serine in the form of phosphatidyl serine.
C) Ethanolamine, in the form of phosphatidyl ethanolamine, can be converted to phosphatidyl choline.
D) Ethanolamine can exchange reversibly with the serine of phosphatidyl serine.
E) The carbons of ethanolamine cannot be derived from glucose but may be derived from fatty acids.

Question 39

Transfer of cholesterol from membranes to HDL requires

A) serum albumin.
B) lecithin cholesterol acyltransferase.
C) cholic acid conjugation.
D) lipoprotein lipase.
E) partial hydrolysis.

Question 40

Which of the following statements about chylomicrons is FALSE?

A) chylomicrons transport dietary lipids.
B) chylomicrons are synthesized in the liver.
C) chylomicron remnants are internalized by the liver.
D) chylomicrons have a very high ratio of lipid to protein.
E) Lipoprotein lipase catalyzes the hydrolysis of lipid from the chylomicrons.

Question 41

Select the lipid fraction in blood which is most rapidly cleared?

A) VLDL
B) HDL
C) chylomicrons
D) LDL
E) All are cleared at approximately same rate.

Question 42

The lipoproteins made de novo in the intestine or liver and secreted into the bloodstream are

A) chylomicrons, LDL and HDL.
B) VLDL, LDL and HDL.
C) chylomicrons, IDL and HDL.
D) VLDL, IDL and LDL.
E) chylomicrons, VLDL and HDL.

Question 43

Very low density serum lipoproteins (VLDL) transport

A) non-esterified fatty acids to the liver.
B) medium chain non-esterified fatty acids via the lymphatic system.
C) non-esterified fatty acids to the adipose tissues.
D) triacylglycerol from the liver to the adipose tissues.
E) cholesterol from the intestine to the liver.

Question 44

Phosphatidic acid may be the direct or indirect precursor of each of the following lipids EXCEPT

A) phosphatidylcholine
B) phosphatidylglycerol
C) phosphatidylserine
D) Triacylglycerol
E) Glucocerebroside

Question 45

The committed step in steroid biosynthesis from cholesterol is

A) cholesterol esterase conversion of cholesterol ester to free cholesterol.
B) conversion of cholesterol to pregnenolone.
C) the P450 dependent 21-hydroxylation of progesterone.
D) the 17-hydroxylation of pregnenolone to 17-alpha-hydroxypregnenolone.
E) None of the above.

Question 46

During cholesterol biosynthesis the production of HMG CoA involves a condensation reaction of

A) acetyl CoA and malonyl CoA which is reversible.
B) acetyl CoA and malonyl CoA which is irreversible.
C) acetyl CoA and acetoacetyl CoA which is reversible.
D) acetyl CoA and acetoacetyl CoA which is irreversible.

Question 47

Which of the following compounds contain an N-acyl fatty acid?

A) ganglioside
B) lecithin
C) leukotriene
D) plasmalogen
E) sphingosine

Question 48

In the biosynthesis of cholesterol from Acetoacetyl CoA and Acetyl CoA, all of the following metabolites are intermediates, EXCEPT:

A) Dimethylallyl pyrophosphate
B) Malonyl CoA
C) Isopentenyl pyrophosphate
D) Mevalonate
E) Farnesyl pyrophosphate

Question 49

Internalization of the LDL receptor occurs in specialized regions of membrane known as:

A) Endocytotic blebs
B) Microvilli
C) Coated pits
D) Gap junctions
E) Plasma membrane patches

Question 50

Which of the following reactions is inhibited by aspirin?

A) phosphatidylcholine => arachidonic acid + 1-acylphosphatidyl choline.
B) Arachidonic acid => PGH2
C) PGH2 => PGI2
D) PGE2 => 13,14-dihydro-15-keto-PGE2
E) 15-keto-PGE2 => 13,14-dihydro-15-keto-PGE2

Question 51

To be defined as a ganglioside, a lipid substance isolated from nerve tissue must contain in its structure

A) an N-acyl fatty acid derivative of sphingosine plus a hexose.
B) N-acetylneuraminic acid (NANA), N-acetylgalactosamine, a hexose, long chain fatty acid and sphingosine.
C) N-acetylneuraminic acid (NANA), a hexose, a fatty acid and sphingosine.
D) NANA, a hexose, a fatty acid, sphingosine and phosphatidylcholine.
E) a 9 carbon 3-deoxy-5-amino sugar called neuraminic acid, sphingosine and ethanolamine.

Question 52

In complete biosynthesis of sphingomyelin, all the following are required EXCEPT

A) palmitoyl-CoA.
B) L-serine.
C) choline.
D) CDP-diglyceride.
E) NADPH.

Question 53

The first sterol synthesized metabolically in man from acetate is

A) 7-dehydrocholesterol
B) desmosterol
C) cholesterol
D) lanosterol
E) squalene

Question 54

All of the following statements about chylomicron metabolism are true EXCEPT which one?

A) chylomicrons donate apoprotein B to HDL.
B) Another lipoprotein donates apoprotein C to chylomicrons.
C) Lipoprotein lipase degrades chylomicron triglyceride.
D) The end product of chylomicron metabolism in the circulation is called a remnant particle.
E) The liver removes the final component of chylomicron metabolism from the circulation.

Question 55

Lipoprotein lipase

A) hydrolyzes triacylglycerols in the lumen of the intestine.
B) is found in lysosomes.
C) hydrolyzes triacylglycerols in lipoproteins such as chylomicrons and VLDL.
D) converts cholesteryl esters to free cholesterol in high-density lipoproteins.
E) hydrolyzes phosphatidylcholine (lecithin) to lysophosphatidyl choline (lysolecithin).

Question 56

The acyl donor for cholesterol ester formation in blood is

A) phosphatidylcholine.
B) palmitoyl-CoA.
C) triglycerides.
D) acyl carrier protein.
E) monoglycerides.

Question 57

Prostaglandins

A) generally are secreted by one tissue and exert their effects on a different target tissue.
B) stimulate protein synthesis at the transcriptional level.
C) are degraded primarily by the liver.
D) all stimulate the production of cAMP.
E) may be rapidly inactivated at their site of production by a specific prostaglandin dehydrogenase.

Question 58

Sulfatides are synthesized in a reaction between

A) ceramide and S-adenosylmethionine (SAM).
B) ceramide and phosphoadenosine phosphosulfate (PAPS).
C) galactocerebroside and PAPS.
D) galactocerebroside and H2SO4.
E) sphingomyelin and PAPS.

Question 59

Which of the substances below is released from lipids of the plasma membrane and provides the precursor of prostaglandins, thromboxanes and leukotrienes?

A) a fatty acyl CoA
B) a polyunsaturated fatty acid esterified to cholesterol
C) a diacyl glycerol
D) a polyunsaturated fatty acid
E) a saturated fatty acid

Question 60

Tay-Sachs disease is the result of an inborn error of metabolism of

A) histidine.
B) cholesterol.
C) ganglioside.
D) lactose.
E) cerebroside.

Question 61

The action of a phospholipase C on a phospholipid substrate may yield

A) glycerol, fatty acids, inositol 1,4,5-trisphosphate.
B) monoacylglycerol, fatty acid, phosphocholine.
C) diacylglycerol, phosphoethanolamine.
D) phosphoceramide, choline.

Question 62

Materials that accumulate in the brain and other tissues of patients afflicted with the various lipidoses all contain as a common structural feature

A) phosphatidic acid structure.
B) polypeptide residue.
C) ceramide structure.
D) triglyceride structure.
E) sialic acid structure.

Question 63

A molecule of sphingomyelin is similar to a molecule of lysolecithin in that both contain

A) an N-linked fatty acid residue.
B) only one fatty acid residue.
C) an ethanolamine residue.
D) a residue of glycerol.
E) phosphorus, nitrogen and sulfur.

Question 64

The enzyme phosphatidate phosphatase

A) cleaves a fatty acid from the 1 position of phosphatidic acid.
B) cleaves phosphate from the 3 position of phosphatidic acid.
C) cleaves a fatty acid from the 2 position of phosphatidic acid.
D) cleaves phosphate from the 2 position of phosphatidic acid.
E) catalyzes the formation of a phosphodiester.

Question 65

Of the apoproteins listed below, which one is recognized by the LDL receptor?

A) Apoprotein D
B) Apoprotein C II
C) Apoprotein B?48
D) Apoprotein B?100
E) Apoprotein A?I

Question 66

A general enzyme for the esterification of intracellular cholesterol is

A) lecithin-cholesterol acyl transferase.
B) acyl-CoA-cholesterol acyl transferase.
C) cholesterol esterase.
D) CoA transferase.
E) none of the other Answers is correct.

Question 67

An accumulation of gangliosides in brain tissue most likely arises from a deficiency of lysosomal

A) acyltransferase.
B) aryl sulfatase.
C) hexosaminidase.
D) phospholipase A2.
E) sphingomyelinase.

Question 68

Glucocorticoid inhibition of phospholipase A2 has the effect of inhibiting the synthesis of

A) prostaglandins, but not thromboxanes, leukotrienes, and arachidonic acid.
B) prostaglandins and thromboxanes, but not leukotrienes and arachidonic acid.
C) prostaglandins, thromboxanes, and leukotrienes but not arachidonic acid.
D) prostaglandins, thromboxanes, leukotrienes, and arachidonic acid.

Question 69

Sphingosine is a product of the condensation of

A) acetyl-CoA and malonyl-CoA
B) CDP-choline and 1,2-diacylglycerol
C) ceramide and CDP-choline
D) palmitoyl-CoA and serine
E) palmitoyl-CoA and acetyl-CoA

Question 70

Cerebrosides can be formed by the contribution of all of the following, EXCEPT

A) glucose.
B) serine.
C) palmitic acid.
D) glycerol.
E) long chain fatty acid.

Question 71

Which statement is false concerning farnesyl pyrophosphate?

A) It is an eventual product of activated isoprenes.
B) It is a product of Squalene.
C) It is involved in prenylation of proteins where the first step is transfer of the farnesyl group to the protein and loss of the phosphates.
D) It is made during the synthesis of cholesterol.
E) Its formation would, at least partly, be inhibited by Lovastatin.

Question 72

An LDL receptor deficiency could cause all of the following to occur EXCEPT

A) decreased serum LDL.
B) increased cholesterol synthesis.
C) increased serum cholesterol.
D) decreased LDL endocytosis.
E) increased 3-hydroxy-3-methyl glutaryl-CoA reductase activity.

Question 73

Which lipoprotein contains the lowest ratio of lipid to protein?

A) chylomicrons
B) HDL
C) IDL
D) LDL
E) VLDL

Question 74

Which of the following metabolic pathways is CORRECT?

A) lanosterol --> squalene --> mevalonate --> cholesterol
B) acetyl CoA --> hydroxymethylglutaryl CoA --> mevalonate --> lanosterol
C) mevalonate --> hydroxymethylglutaryl CoA --> squalene --> cholesterol
D) mevalonate --> lanosterol --> squalene --> cholesterol

Question 75

Premature infants may exhibit the respiratory distress syndrome due to inadequate secretion of

A) sphingomyelin
B) dioleoyl phosphatidyl inositol.
C) dipalmitoleoyl phosphatidylcholine
D) cholesterol.
E) dipalmitoyl phosphatidyl choline.

Question 76

Squalene is the immediate precursor of

A) desmosterol.
B) farnesyl pyrophosphate.
C) geranyl pyrophosphate.
D) cholesterol.
E) lanosterol.

Question 77

An important function of high density lipoproteins (HDL) is the

A) acquisition of cholesterol from tissues and other lipoproteins.
B) deposition of cholesteryl esters in atherosclerotic lesions.
C) transport of bile lipids from liver to gall bladder.
D) transport of glycerophospholipids from liver to intestine.
E) transport of triacylglycerols from liver to adipose.

Question 78

The substrate for the synthesis of prostaglandins and leukotrienes is released from endogenous

A) gangliosides.
B) plasmalogen.
C) phosphatidylcholine.
D) cholesteryl oleate.
E) ceramide.

Question 79

Prostacyclin (PGI) is

A) a potent platelet aggregator.
B) a potent smooth muscle relaxer (vasodilator).
C) a potent smooth muscle contractor (vasoconstrictor).
D) the long sought slow-reacting substance of anaphylaxis (SRSA).
E) formed from arachidonic acid by the action of lipoxygenase.

Question 80

Which of the following apoproteins serves as a cofactor (activator) for lecithin: cholesterol acyltransferase (LCAT)?

A) APO AI
B) APO B-100
C) APO CII
D) APO E