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Biochemistry (Questions) > 554 - 603 Cholesterol and Bile acids > Flashcards

554 - 603 Cholesterol and Bile acids Flashcards

1
Q

Which substrates are necessary for the synthesis of bile salts?

Select one or more:
a. NADPH2
b. NADH2
c. ATP
d. O2
e. H2O

A

a. NADPH2
c. ATP
d. O2

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2
Q

What is the subcellular localization of the side chain cleavage enzyme in adrenal fascicular cells?

Select one:
a. Golgi membranes
b. mitochondria
c. nuclear membrane
d. plasma membrane
e. rough endoplasmic reticulum

A

b. mitochondria

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3
Q

What is the weakly androgenic steroid that is synthesized in the fascicular zone of the adrenal gland?

Select one:
a. testosterone
b. progesterone
c. pregnenolone
d. dehydroepiandrosterone
e. corticosterone

A

d. dehydroepiandrosterone

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4
Q

Select the statements valid for the lipoproteins

Select one or more:
a. Their density increases in parallel with their protein content
b. Their density is reciprocally proportional to their lipid content
c. The core non-polar lipids are surrounded by polar lipids
d. All of them contain phospholipids
e. Non-polar interactions bind together the lipids in their structure

A

All are correct

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5
Q

Which of the following statements are valid for the apolipoprotein B-100?

Select one or more:
a. It is synthesized in the liver
b. It is recognized by the LDL-receptor
c. It is not present in the structure of VLDL
d. It participates in the liver uptake of chylomicron remnants
e. It is found in the structure of IDL

A

a. It is synthesized in the liver
b. It is recognized by the LDL-receptor
e. It is found in the structure of IDL

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6
Q

Which of the following lipoproteins does not contain triacylglycerols?

Select one:
a. Chylomicron
b. HDL3
c. IDL
d. Nascent VLDL
e. VLDL

A

b. HDL3
(HDL3 carries enzymes that prevent oxidative stress and receives cholesterol from reverse cholesterol transport through the ATP-binding cassette transporter A1 mediators )

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7
Q

Which of the following statements is not valid for the lipoprotein lipase?

Select one:
a. An isoenzyme with a low KM is present in the mammary gland
b. It degrades the majority of plasma triacylglycerols
c. It is bound to the luminal surface of the capillary endothelial cells
d. Its activity increases in the fasting state
e. VLDL carries its cofactor

A

d. Its activity increases in the fasting state

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8
Q

Which of the following statements are valid?
Select one or more:
a. The nascent VLDL is formed in the intestinal epithelial cells
b. The VLDL is converted to IDL in the circulation
c. The cells recognize the apo B-100 in the structure of VLDL and take up the lipoprotein through it
d. The lipoprotein lipase reduces the triacylglycerol content of VLDL
e. The apo B-100 of LDL is derived from VLDL

A

b. The VLDL is converted to IDL in the circulation
d. The lipoprotein lipase reduces the triacylglycerol content of VLDL
e. The apo B-100 of LDL is derived from VLDL

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9
Q

Which of the following statements is not valid?

Select one:
a. Cholesterol overload inhibits the expression of LDL-receptors
b. Cholesterol overload inhibits the HMG-CoA reductase in the cells
c. In case of cholesterol overproduction cholesteryl esters are formed in the cells as a result of the action of LCAT enzyme
d. The LDL-derived cholesterol affects the cholesterol synthesis in the cells
e. The LDL-receptor recognizes the apo B-100

A

c. In case of cholesterol overproduction cholesteryl esters are formed in the cells as a result of the action of LCAT enzyme

(Lecithin–cholesterol acyltransferase is an enzyme, in many animals including humans, that converts free cholesterol into cholesteryl ester)

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10
Q

Select the statements valid for the bile acids

Select one or more:
a. The bile acids are synthesized in the intestine
b. In the course of synthesis the polar character of the molecules increases
c. Bile acids are necessary for the solubilization of cholesterol in water phase
d. Deoxycholic acid is one of the primary bile acids
e. Lack of bile acids results in steatorrhea

A

b. In the course of synthesis the polar character of the molecules increases
c. Bile acids are necessary for the solubilization of cholesterol in water phase
e. Lack of bile acids results in steatorrhea

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11
Q

Which is the committed step of the cholesterol biosynthesis?

Select one:
a. Mevalonate to 5-phosphomevalonate
b. Acetyl-CoA to acetoacetyl-CoA
c. Acetoacetyl-CoA to 3-hydroxi-3-methyl glutaryl-CoA
d. 5-phosphomevalonate to 5-pyrophosphomevalonate
e. 3-hydroxi-3-methyl glutaryl-CoA to Mevalonate

A

e. 3-hydroxi-3-methyl glutaryl-CoA to Mevalonate

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12
Q

Which is the committed step of the cholesterol biosynthesis?

Select one:
a. Mevalonate to 5-phosphomevalonate
b. Acetyl-CoA to acetoacetyl-CoA
c. Acetoacetyl-CoA to 3-hydroxi-3-methyl glutaryl-CoA
d. 5-phosphomevalonate to 5-pyrophosphomevalonate
e. 3-hydroxi-3-methyl glutaryl-CoA to Mevalonate

A

e. 3-hydroxi-3-methyl glutaryl-CoA to Mevalonate

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13
Q

Select the correct statements

Select one or more:
a. The nascent HDL does not contain cholesteryl esters
b. Triacylglycerols are transferred from VLDL to HDL
c. Cholesteryl esters are transferred from VLDL to HDL
d. The hepatic lipase degrades the triacylglycerols in HDL2
e. The HDL-derived cholesterol is taken up by the liver in part in the form of LDL

A

a. The nascent HDL does not contain cholesteryl esters
b. Triacylglycerols are transferred from VLDL to HDL
d. The hepatic lipase degrades the triacylglycerols in HDL2
e. The HDL-derived cholesterol is taken up by the liver in part in the form of LDL

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14
Q

Select the wrong statement

Select one:
a. HDL carries ACAT (acyl-CoA cholesterol acyltransferase)
b. HDL takes up triacylglycerols with the help of cholesteryl ester transfer protein
c. HDL2 delivers cholesterol to the liver
d. The HDL contains apo-A1
e. The triacylglycerol content of HDL2 is higher than that of HDL3

A

a. HDL carries ACAT (acyl-CoA cholesterol acyltransferase)

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15
Q

At least how many glucose molecules are necessary to provide the carbon atoms for the biosynthesis of one cholesterol molecule in mammalian tissues?

Select one:
a. 7
b. 8
c. 9
d. 6
e. 5

A

c. 9

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16
Q

Which of the following statements are valid for the ABCA1 transporter?

Select one or more:
a. It is the major transporter of bile salts
b. Its deficiency causes atherosclerosis because of the elevated levels of LDL-cholesterol
c. High intracellular cholesterol content stimulates its transcription
d. It is necessary for the efflux of cholesterol from the cells
e. It is a scavenger receptor for LDL
f. HDL binds to it

A

c. High intracellular cholesterol content stimulates its transcription
d. It is necessary for the efflux of cholesterol from the cells

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17
Q

Which processes are modulated by the amount of intracellular free cholesterol?

Select one or more:
a. synthesis of bile acids
b. down-regulation of LDL-receptors in the membrane
c. transfer of cholesterol from the membrane into HDL
d. cholesterol synthesis
e. synthesis of cholesterol esters

A

a. synthesis of bile acids
c. transfer of cholesterol from the membrane into HDL
d. cholesterol synthesis
e. synthesis of cholesterol esters

(The percentage decrease in LDL receptor activity correlated with the percentage increase in LDL cholesterol (r = -0.796, p = 0.06, n = 6). Thus, high levels of dietary cholesterol can down-regulate the LDL receptor in humans.)

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18
Q

Which carbon atom carries the hydroxylic group in cholesterol?
Select one:

a. C-3
b. C-7
c. C-10
d. C-21
e. C-27

A

a. C-3

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19
Q

Which statements are true?

Select one or more:
a. Cholesterol is formed from HMG-CoA synthesized in the mitochondria
b. Cholesterol is formed from HMG-CoA synthesized in the cytosol
c. Mevalonate is formed from HMG-CoA by decarboxylation
d. NADPH is needed for mevalonate synthesis
e. Acetyl-CoA for cholesterol synthesis originates from mitochondria

A

b. Cholesterol is formed from HMG-CoA synthesized in the cytosol
d. NADPH is needed for mevalonate synthesis
e. Acetyl-CoA for cholesterol synthesis originates from mitochondria

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20
Q

Cholesterol is synthesized from:

Select one:
a. oxalate.
b. malate.
c. lipoic acid.
d. choline.
e. acetyl-CoA.

A

e. acetyl-CoA.

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21
Q

Which of these statements about the regulation of cholesterol synthesis is not true?

Select one:
a. Cholesterol acquired in the diet has essentially no effect on the synthesis of cholesterol in the liver.
b. Failure to regulate cholesterol synthesis predisposes humans to atherosclerosis.
c. High intracellular cholesterol stimulates formation of cholesterol esters.
d. Insulin stimulates HMG-CoA reductase.
e. Cholesterol exerts a negative feedback effect on HMG-CoA reductase.

A

a. Cholesterol acquired in the diet has essentially no effect on the synthesis of cholesterol in the liver.

22
Q

Where is acyl-CoA cholesterol-transferase (ACAT) localized?

Select one:
a. endoplasmic reticulum membrane
b. cytosol
c. mitochondrium matrix
d. inner mitochondrial membrane

A

a. endoplasmic reticulum membrane

23
Q

Which process is inhibited, if MTP (microsomal TG transfer protein) inhibitor is used as a drug?

Select one:
a. TG (triglyceride) transfer into adipocytes
b. TG (triglyceride) transfer into hepatocytes
c. cholesteryl ester transfer into lipid droplets
d. cholesteryl ester transfer into chylomicrons

A

d. cholesteryl ester transfer into chylomicrons

24
Q

How many Acetyl-CoA molecules are needed for the synthesis of one molecule of cholesterol?

Select one:
a. 10
b. 18
c. 20
d. 25

A

b. 18

25
Q

Where is the SREBP regulator domain localized if there is excess cholesterol in the cell?

Select one:
a. cytosol
b. endoplasmic reticulum
c. Golgi
d. nucleus

A

b. endoplasmic reticulum

26
Q

Which protein of the SREBP-dependent signalling binds directly cholesterol?

Select one:
a. SCAP
b. SREBP
c. INSIG
d. SREBP-cleavage protease

A

a. SCAP

27
Q

What is the consequence of increased release of PCSK9?

Select one:
a. enhanced LDL uptake in hepatocytes
b. increased number of LDL receptors in hepatocytes
c. lower blood plasma LDL level
d. higher blood plasma LDL level

A

d. higher blood plasma LDL level

( Proprotein convertase subtilisin/kexin type 9 (PCSK9): Ser-Protease, decreases LDL-Rec number by promoting lysosomal degradation LDL-rec deficiency leads to high plasma cholesterol levels – a risk factor for atherosclerosis)

28
Q

What is the consequence of enhanced IDOL production in the liver?

Select one:
a. enhanced LDL uptake in the liver
b. higher number of LDL-receptors in the hepatocytes
c. higher blood plasma LDL level
d. lower blood plasma LDL level

A

c. higher blood plasma LDL level

(Inducible degrader of LDL receptor (IDOL):
an Ubiquitin-ligase, promotes the proteasomal degradation of the LDL-Receptors)

29
Q

What is the function of the cholesteryl ester transfer protein (CETP)?

Select one:
a. transfers cholesteryl esters from extrahepatic cells to HDL
b. transfers cholesteryl esters from HDL to VLDL
c. transfers cholesteryl esters from the intestine to HDL
d. transfers cholesteryl esters from HDL to the liver

A

b. transfers cholesteryl esters from HDL to VLDL
(3. CETP: Cholesteryl-Ester-Transfer Protein)

30
Q

What is the function of scavenger receptor B1 (SR-B1)?

Select one:
a. LDL endocytosis
b. HDL endocytosis
c. selective uptake of LDL-cholesterol
d. selective uptake of HDL-cholesterol

A

d. selective uptake of HDL-cholesterol

(hepatic lipase and SR-B1 (scavenger receptor B1) cooperate: discoid HDL is regenerated – can start a new round)

31
Q

What chemical changes occur when primary bile acids are converted to secondary bile acids?

Select one:
a. removal of carboxylic groups
b. reduction of the double bond at 3C
c. removal of the 3C-hydroxylic group
d. removal of the 7C-hydroxylic group

A

removal of the 7C-hydroxylic group
(7alpha-Hydroxylase in the liver does not recognize the secondary BAs, so no way back to primary BAs)

32
Q

Which value approaches most closely the daily rate of cholesterol synthesis in the liver (X) and in the extrahepatic tissues (Y) in adults (70 kg body weight)? Numbers are in mg cholesterol synthesized per kg organ mass.

Select one:
a. X=10; Y=1000
b. X=100; Y=100
c. X=250; Y=10
d. X=500; Y=1
e. X=1000; Y=0

A

c. X=250; Y=10

33
Q

Which proteins are needed for the transfer of dietary cholesterol to extrahepatic tissues?

Select one or more:
a. apoB48
b. apoB100
c. lipoprotein lipase
d. acyl-CoA cholesterol acyl transferase
e. lecithin cholesterol acyl transferase

A

a. apoB48
b. apoB100 (recognized by LDL receptor)
c. lipoprotein lipase
d. acyl-CoA cholesterol acyl transferase

34
Q

Which proteins are needed for the transfer of dietary cholesterol to extrahepatic tissues?

Select one or more:
a. apoB48
b. apoB100
c. lipoprotein lipase
d. acyl-CoA cholesterol acyl transferase
e. lecithin cholesterol acyl transferase

A

a. apoB48
b. apoB100 (recognized by LDL receptor)
c. lipoprotein lipase
d. acyl-CoA cholesterol acyl transferase

35
Q

Which statements are true concerning proprotein convertase subtilisin- like/kexin type 9 (PCSK9)?

Select one or more:
a. it contributes to the intracellular processing of LDL receptors prior their exposure in the membrane
b. it stimulates the degradation of LDL receptors
c. it triggers the endocytosis of LDL-receptor
d. it binds to LDL receptors
e. it is a protease that degrades LDL receptors

A

b. it stimulates the degradation of LDL receptors
c. it triggers the endocytosis of LDL-receptor
d. it binds to LDL receptors

36
Q

Which statements are true concerning Idol (inducer of degradation of LDL receptor)?

Select one or more:
a. it is a transcription factor controlling PCSK9 (proprotein convertase subtilisin-like/kexin type 9)
b. it is a protease that degrades LDL receptor
c. it binds LDL receptors extracellularly
d. it is under the control of LXR (liver X receptor)
e. it stimulates the ubiquitination of LDL receptor

A

d. it is under the control of LXR (liver X receptor)
e. it stimulates the ubiquitination of LDL receptor

37
Q

Which statements are true concerning FXR (farnesoid X receptor)?

Select one or more:
a. it operates in fibroblasts, hepatocytes and intestinal epithelial cells
b. its ligands are bile acids
c. in fibroblasts it induces FGF19 (fibroblast growth factor 19)
d. in hepatocytes it induces 7a-hydoxylase
e. in intestinal epithelial cells it induces IBAT (ileal bile acid transporter)

A

b. its ligands are bile acids
e. in intestinal epithelial cells it induces IBAT (ileal bile acid transporter)

38
Q

Which statements are true concerning miR-33 microRNA?

Select one or more:
a. its level increases in cholesterol depletion
b. its level increases in cholesterol overload
c. it stimulates the translation of ABCA1 (ATP binding cassette A 1 transporter)
d. it stimulates the transcription of NPC1 (Nieman-Pick type C 1 protein)
e. it suppresses the translation of ABCA1 (ATP binding cassette A 1 transporter)

A

a. its level increases in cholesterol depletion
e. it suppresses the translation of ABCA1 (ATP binding cassette A 1 transporter)

39
Q

Select the factors that cause increase of the plasma LDL-cholesterol level

Select one or more:
a. LDL-receptor deficiency
b. Apo-B100 deficiency
c. lipoprotein lipase deficiency
d. PCSK9 (proprotein convertase subtilisin-like/kexin type 9) deficiency e. Idol (inducer of degradation of LDL receptor) deficiency

A

a. LDL-receptor deficiency
b. Apo-B100 deficiency

40
Q

What is the biological role of bile acids?

Select one or more:
a. they contribute to the interfacial activation of pancreatic lipase in the intestine
b. their micelles are essential for cholesterol absorption in the intestine c. they are ligands of FXR (farnesoid X receptor)
d. their micelles are essential for cholesterol disposal in the intestine
e. they are ligands of LXR (liver X receptor)

A

a. they contribute to the interfacial activation of pancreatic lipase in the intestine
b. their micelles are essential for cholesterol absorption in the intestine c. they are ligands of FXR (farnesoid X receptor)
d. their micelles are essential for cholesterol disposal in the intestine

41
Q

Which reactions participate in the bile acid synthesis?

Select one or more:
a. 7alfa hydroxylation
b. 7beta hydroxylation
c. 12alfa hydroxylation
d. glycine conjugation
e. glutamine conjugation

A

a. 7alfa hydroxylation
c. 12alfa hydroxylation
d. glycine conjugation

42
Q

What is the recommended daily allowance of cholesterol in normal mixed- type diet of adults?

Select one:
a. 0.5 g
b. 1 g
c. 2 g
d. 10 g
e. 100 g

A

a. 0.5 g

43
Q

In what form are the C-atoms of cholesterol released from the human body?

Select one or more:
a. CO2
b. free cholesterol
c. cholesteryl esters
d. cholate
e. bilirubin

A

a. CO2
b. free cholesterol
d. cholate

44
Q

In what form is cholesterol released by the liver?

Select one:
a. chylomicron
b. VLDL
c. LDL
d. IDL
e. in complex with albumin

A

b. VLDL

45
Q

In what form is cholesterol taken up by the liver?

Select one or more:
a. chylomicron
b. chylomicron remnant
c. HDL
d. LDL
e. VLDL

A

b. chylomicron remnant
c. HDL
d. LDL

46
Q

Select the correct order of enzymes or transporters operating in the disposal of excess cholesterol from the human body?

Select one:
a. ABCA1 / LCAT / LDL / IDL / BSEP
b. ABCA1 / LCAT / LDL / VLDL / BSEP
c. ACAT / ABCA1 / HDL / LDL / BSEP
d. ABCA1 / LCAT / HDL / CETP / LDL
e. ABCA1 / ACAT / LCAT / HDL / LDL

A

e. ABCA1 / ACAT / LCAT / HDL / LDL

( 1. ABCA1 pumps cholesterol out of the cells using ATP
Cholesterol esterification on HDL: LCAT

47
Q

Which cells express FXR?

Select one or more:
a. hepatocytes
b. enterocytes
c. macrophages
d. adipocytes
e. smooth muscle cells

A

a. hepatocytes
b. enterocytes

48
Q

Which cells express LXR?
Select one or more:
a. hepatocytes
b. enterocytes
c. macrophages
d. adipocytes
e. smooth muscle cells

A

a. hepatocytes
b. enterocytes
c. macrophages
d. adipocytes
e. smooth muscle cells

49
Q

Which statements are true regarding the lecithin cholesterol acyl transferase?

Select one or more:
a. It is one of the enzymes of cholesterol synthesis.
b. It forms cholesteryl esters.
c. It is localized in the membrane of the endoplasmic reticulum.
d. Apo AI is its activator.
e. It is active in phosphorylated state.

A

b. It forms cholesteryl esters.
d. Apo AI is its activator.

50
Q

Which statements are true regarding the synthesis of cholesterol in mammalians?

Select one or more:
a. Cholesterol is synthesized only in the liver.
b. The rate of cholesterol synthesis is constant.
c. Cholesterol inhibits the activity of 3-hydroxy 3-methyl glutaryl-CoA reductase
d. Cholesterol inhibits the transcription of 3-hydroxy 3-methyl glutaryl-CoA reductase
e. Cholesterol inhibits the degradation of 3-hydroxy 3-methyl glutaryl-CoA reductase

A

c. Cholesterol inhibits the activity of 3-hydroxy 3-methyl glutaryl-CoA reductase
d. Cholesterol inhibits the transcription of 3-hydroxy 3-methyl glutaryl-CoA reductase

51
Q

Which metabolic pathway uses the reaction catalyzed by 3-hydroxy 3-methyl glutaryl-CoA reductase?

Select one:
a. glycolysis
b. synthesis of ketone bodies
c. oxidation of fatty acids
d. synthesis of fatty acids
e. synthesis of cholesterol

A

e. synthesis of cholesterol

52
Q

Where is the 3-hydroxy 3-methyl glutaryl-CoA reductase localized within the cell?

Select one:
a. cytosol
b. membrane of the endoplasmic reticulum
c. matrix of mitochondria
d. the inner membrane of mitochondria
e. the outer membrane of mitochondria

A

b. membrane of the endoplasmic reticulum

Biochemistry (Questions) (35 decks)

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