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biochem 2 > membrane lipid b and steroid iosynthesis > Flashcards

membrane lipid b and steroid iosynthesis Flashcards

1
Q

Which of the following functions does cholesterol serve in biological systems?
a) Acts as an antioxidant
b) Regulates blood pH
c) Modulates membrane fluidity
d) Initiates protein synthesis

A

c) Modulates membrane fluidity

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2
Q

In cholesterol biosynthesis, where does stage 1 occur?
a) Nucleus
b) Golgi apparatus
c) Cytoplasm
d) Mitochondria

A

c) Cytoplasm

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3
Q

How many carbon atoms are derived from acetyl CoA in the synthesis of cholesterol?
a) 18
b) 24
c) 27
d) 30

A

c) 27

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4
Q

Which stage of cholesterol biosynthesis takes place in the endoplasmic reticulum (ER)?
a) Stage 1
b) Stage 2
c) Stage 3
d) Stages 2 and 3

A

d) Stages 2 and 3

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5
Q

What is the precursor molecule for cholesterol biosynthesis?
a) Glyceraldehyde-3-phosphate
b) Pyruvate
c) Isopentenyl pyrophosphate
d) Acetylcholine

A

c) Isopentenyl pyrophosphate

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6
Q

Which enzyme catalyzes the irreversible reduction of HMG CoA to mevalonate in Stage 1 of cholesterol biosynthesis?
a) Acetyl CoA synthase
b) HMG-CoA reductase
c) Isopentenyl pyrophosphate synthase
d) Squalene cyclase

A

b) HMG-CoA reductase

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7
Q

What is the immediate precursor of mevalonate in cholesterol biosynthesis?
a) Isopentenyl pyrophosphate
b) Acetyl CoA
c) Farnesyl pyrophosphate
d) HMG CoA

A

d) HMG CoA

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8
Q

How many consecutive ATP-requiring reactions are involved in converting mevalonate into 3-isopentenyl pyrophosphate?
a) One
b) Two
c) Three
d) Four

A

c) Three

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9
Q

What is the primary product of Stage 1 in cholesterol biosynthesis?
a) Squalene
b) Mevalonate
c) Isopentenyl pyrophosphate
d) HMG CoA

A

b) Mevalonate

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10
Q

Which of the following statements accurately describes HMG-CoA reductase?
a) It catalyzes the conversion of mevalonate to HMG CoA.
b) It catalyzes the conversion of HMG CoA to mevalonate.
c) It is an enzyme involved in squalene cyclization.
d) It is activated by ATP.

A

b) It catalyzes the conversion of HMG CoA to mevalonate.

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11
Q

How many molecules of isopentenyl pyrophosphate condense to form squalene in Step 2 of cholesterol biosynthesis?
a) Three
b) Four
c) Five
d) Six

A

d) Six

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12
Q

What is the initial condensation product formed in the synthesis of squalene?
a) Dimethylallyl pyrophosphate
b) Isopentenyl pyrophosphate
c) Geranyl pyrophosphate
d) Squalene pyrophosphate

A

c) Geranyl pyrophosphate

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13
Q

Which enzyme catalyzes the formation of geranyl pyrophosphate from two isomeric C5 units?
a) Isopentenyl pyrophosphate synthase
b) Squalene synthase
c) Geranyl transferase
d) Dimethylallyl pyrophosphate synthase

A

c) Geranyl transferase

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14
Q

How many carbon atoms are present in squalene, the final product of Step 2?
a) 20
b) 25
c) 30
d) 35

A

c) 30

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15
Q

Which statement accurately describes the condensation process in Step 2 of cholesterol biosynthesis?
a) Five molecules of isopentenyl pyrophosphate are condensed to form geranyl pyrophosphate.
b) Geranyl pyrophosphate is formed by the condensation of six molecules of dimethylallyl pyrophosphate.
c) Squalene is synthesized directly from isopentenyl pyrophosphate without any intermediate steps.
d) The condensation process involves the formation of geranyl pyrophosphate, which subsequently cyclizes to form squalene.

A

d) The condensation process involves the formation of geranyl pyrophosphate, which subsequently cyclizes to form squalene.

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16
Q

Which enzyme catalyzes the reductive tail-to-tail condensation of two molecules of farnesyl pyrophosphate to yield squalene?
a) Squalene synthase
b) Geranyl transferase
c) Isopentenyl pyrophosphate synthase
d) Dimethylallyl pyrophosphate synthase

A

a) Squalene synthase

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17
Q

What are the products of the reaction catalyzed by squalene synthase?
a) Squalene and NADPH
b) Squalene and pyruvate
c) Squalene, PPi, NADP+, and H+
d) Farnesyl pyrophosphate and NADPH

A

c) Squalene, PPi, NADP+, and H+

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18
Q

Where does the formation of squalene occur within the cell?
a) Golgi apparatus
b) Mitochondria
c) Endoplasmic reticulum (ER)
d) Cytoplasm

A

c) Endoplasmic reticulum (ER)

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19
Q

What is the role of NADPH in the formation of squalene?
a) It acts as a cofactor for squalene synthase.
b) It is oxidized to NADP+ during the reaction.
c) It serves as an energy source for the condensation reaction.
d) It is a substrate that forms a complex with squalene.

A

a) It acts as a cofactor for squalene synthase.

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20
Q

How many carbon atoms are present in squalene, the final product of this reaction?
a) 10
b) 15
c) 25
d) 30

A

d) 30

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21
Q

What is the initial activation step required for squalene in Stage 3 of cholesterol biosynthesis?
a) Conversion into lanosterol
b) Conversion into squalene epoxide
c) Conversion into farnesyl pyrophosphate
d) Conversion into isopentenyl pyrophosphate

A

b) Conversion into squalene epoxide

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22
Q

Which molecule is required for the conversion of squalene into squalene epoxide?
a) NADPH
b) ATP
c) NADH
d) ADP

A

a) NADPH

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23
Q

What is the name of the enzyme that catalyzes the cyclization of squalene epoxide to lanosterol?
a) Squalene synthase
b) Oxidosqualene cyclase
c) HMG-CoA reductase
d) Geranyl transferase

A

b) Oxidosqualene cyclase

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24
Q

How many steps are involved in the conversion of lanosterol to cholesterol?
a) 9
b) 12
c) 15
d) 19

A

d) 19

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25
Q

Lanosterol, the intermediate formed in Stage 3, serves as the precursor for which important molecule?
a) Fatty acids
b) Steroid hormones
c) Amino acids
d) Nucleic acids

A

b) Steroid hormones

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26
Q

Where is phosphatidate synthesized in mammals?
a) Golgi apparatus
b) Nucleus
c) Endoplasmic reticulum (ER) and outer mitochondrial membrane
d) Cytoplasm

A

c) Endoplasmic reticulum (ER) and outer mitochondrial membrane

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27
Q

How is phosphatidate formed from glycerol-3-phosphate?
a) Two fatty acids are removed from glycerol-3-phosphate.
b) One fatty acid is added to glycerol-3-phosphate.
c) Two fatty acids are added to glycerol-3-phosphate.
d) Glycerol-3-phosphate is phosphorylated.

A

c) Two fatty acids are added to glycerol-3-phosphate.

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28
Q

Which enzyme catalyzes the addition of two fatty acids to glycerol-3-phosphate to yield phosphatidate?
a) Diacylglycerol kinase
b) Glycerol phosphate acyltransferase
c) Phospholipase A2
d) Phosphatidate phosphatase

A

b) Glycerol phosphate acyltransferase

29
Q

In addition to glycerol-3-phosphate, phosphatidate can also be synthesized from which molecule in a salvage pathway?
a) Phosphatidylserine
b) Phosphatidylcholine
c) Diacylglycerol (DAG)
d) Triacylglycerol

A

c) Diacylglycerol (DAG)

30
Q

What molecules are involved in the conversion of diacylglycerol (DAG) to phosphatidate in the salvage pathway?
a) Diacylglycerol and GTP
b) Diacylglycerol and ATP
c) Phosphatidate and ADP
d) Phosphatidate and ATP

A

b) Diacylglycerol and ATP

31
Q

Where does triacylglycerol synthesis primarily occur?
a) Muscle tissue
b) Kidneys
c) Liver
d) Pancreas

A

c) Liver

32
Q

Which enzyme hydrolyzes phosphatidate to yield diacylglycerol (DAG) during triacylglycerol synthesis?
a) Phospholipase A2
b) Phosphatidic acid phosphatase
c) Glycerol phosphate acyltransferase
d) Diacylglycerol kinase

A

b) Phosphatidic acid phosphatase

33
Q

What is the product of the hydrolysis of phosphatidate by phosphatidic acid phosphatase?
a) Phosphatidylcholine
b) Diacylglycerol (DAG)
c) Phosphatidylserine
d) Phosphatidylglycerol

A

b) Diacylglycerol (DAG)

34
Q

Which enzyme acetylates diacylglycerol (DAG) to form triacylglycerol?
a) Diacylglycerol kinase
b) Diacylglycerol acyltransferase
c) Glycerol phosphate acyltransferase
d) Phospholipase A1

A

b) Diacylglycerol acyltransferase

35
Q

Where are the enzymes phosphatidic acid phosphatase and diacylglycerol acyltransferase associated during triacylglycerol synthesis?
a) Nucleus
b) Golgi apparatus
c) Endoplasmic reticulum (ER) membrane
d) Mitochondrial membrane

A

c) Endoplasmic reticulum (ER) membrane

36
Q

Where does the synthesis of phospholipids primarily occur?
a) Nucleus
b) Cytoplasm
c) Endoplasmic reticulum (ER) and Golgi apparatus
d) Mitochondria

A

c) Endoplasmic reticulum (ER) and Golgi apparatus

37
Q

What is required for phospholipid synthesis to combine phosphatidate with an alcohol?
a) ATP
b) GTP
c) Cytidine triphosphate (CTP)
d) NADPH

A

c) Cytidine triphosphate (CTP)

38
Q

Which molecule reacts with phosphatidate to form the activated diacylglycerol, cytidine diphosphodiacylglycerol (CDP-diacylglycerol)?
a) ATP
b) GTP
c) Cytidine triphosphate (CTP)
d) NADPH

A

c) Cytidine triphosphate (CTP)

39
Q

What is the function of cytidine diphosphodiacylglycerol (CDP-diacylglycerol) in phospholipid synthesis?
a) It serves as a cofactor for phospholipase A2.
b) It is the final product of phospholipid synthesis.
c) It is an intermediate required for phospholipid formation.
d) It inhibits the synthesis of phospholipids.

A

c) It is an intermediate required for phospholipid formation.

40
Q

In which cellular organelles does the formation of cytidine diphosphodiacylglycerol (CDP-diacylglycerol) occur?
a) Nucleus
b) Golgi apparatus
c) Endoplasmic reticulum (ER) and Golgi apparatus
d) Mitochondria

A

c) Endoplasmic reticulum (ER) and Golgi apparatus

41
Q

What molecule reacts with CDP-diacylglycerol to form a phosphodiester linkage?
a) Phosphatidate
b) Alcohol
c) Glycerol
d) ATP

A

b) Alcohol

42
Q

What are the products formed when CDP-diacylglycerol reacts with an alcohol, specifically inositol?
a) Phosphatidylserine and AMP
b) Phosphatidylinositol and CMP
c) Phosphatidylethanolamine and ADP
d) Phosphatidylcholine and GTP

A

b) Phosphatidylinositol and CMP

43
Q

Where is diphosphatidylglycerol (cardiolipin) abundant?
a) Outer mitochondrial membrane
b) Endoplasmic reticulum (ER)
c) Golgi apparatus
d) Inner mitochondrial membrane

A

d) Inner mitochondrial membrane

44
Q

What role does cardiolipin play in cellular processes?
a) Regulation of DNA replication
b) Organization of proteins participating in oxidative phosphorylation
c) Transport of ions across the plasma membrane
d) Synthesis of carbohydrates

A

b) Organization of proteins participating in oxidative phosphorylation

45
Q

What are the products formed when CDP-diacylglycerol reacts with phosphatidylglycerol?
a) Phosphatidylcholine and AMP
b) Phosphatidylserine and GTP
c) Cardiolipin and CMP
d) Phosphatidylglycerol and ADP

A

c) Cardiolipin and CMP

46
Q

What is the major phospholipid of the inner leaflet of cell membranes?
a) Phosphatidylcholine
b) Phosphatidylethanolamine
c) Phosphatidylinositol
d) Phosphatidylserine

A

b) Phosphatidylethanolamine

47
Q

How is alcohol ethanolamine activated for phospholipid synthesis?
a) By acetylation
b) By phosphorylation
c) By oxidation
d) By reduction

A

b) By phosphorylation

48
Q

Which molecule reacts with CTP to form CDP-ethanolamine?
a) Phosphatidate
b) Phosphatidylserine
c) Alcohol ethanolamine
d) Diacylglycerol (DAG)

A

c) Alcohol ethanolamine

49
Q

What happens to the phosphorylethanolamine unit of CDP-ethanolamine during phospholipid synthesis?
a) It is hydrolyzed.
b) It is oxidized.
c) It is transferred to DAG to form phosphatidylethanolamine.
d) It is converted into ATP.

A

c) It is transferred to DAG to form phosphatidylethanolamine.

50
Q

Where is phosphatidylethanolamine predominantly found in cell membranes?
a) Outer leaflet
b) Inner leaflet
c) Bilayer center
d) Membrane surface

A

b) Inner leaflet

51
Q

What is the primary component of ceramide?
a) Glycerol
b) Sphingosine backbone
c) Phosphatidic acid
d) Cholesterol

A

b) Sphingosine backbone

52
Q

Where are sphingolipids highly concentrated within the body?
a) Liver
b) Central nervous system
c) Muscles
d) Kidneys

A

b) Central nervous system

53
Q

What is the structural feature of ceramide?
a) A fatty acid chain attached to a glycerol backbone
b) A fatty acid chain attached to the amino group of a sphingosine backbone
c) A phosphate group attached to a sphingosine backbone
d) A cholesterol molecule attached to a sphingosine backbone

A

b) A fatty acid chain attached to the amino group of a sphingosine backbone

54
Q

What initiates the synthesis of ceramide?
a) Palmitic acid
b) Palmitoyl CoA and serine
c) Sphingosine
d) Dihydroceramide

A

b) Palmitoyl CoA and serine

55
Q

Which enzyme catalyzes the condensation of palmitoyl CoA and serine to form 3-ketosphinganine?
a) Serine dehydrogenase
b) Palmitoyl transferase
c) Serine–palmitoyl transferase
d) Ketosphinganine synthase

A

c) Serine–palmitoyl transferase

56
Q

What is the product of the condensation of palmitoyl CoA and serine?
a) Sphingomyelin
b) 3-ketosphinganine
c) Ceramide
d) Phosphatidylserine

A

b) 3-ketosphinganine

57
Q

What is the immediate precursor of dihydrosphingosine in ceramide biosynthesis?
a) 3-ketosphinganine
b) Palmitoyl CoA
c) Dihydroceramide
d) Sphingomyelin

A

a) 3-ketosphinganine

58
Q

Which molecule is formed by the reduction of 3-ketosphinganine?
a) Dihydroceramide
b) Ceramide
c) Dihydrosphingosine
d) Palmitoyl CoA

A

c) Dihydrosphingosine

59
Q

What is the linkage between the oligosaccharide chain and ceramide in gangliosides?
a) Ester linkage
b) Glycosidic linkage
c) Peptide linkage
d) Phosphodiester linkage

A

b) Glycosidic linkage

60
Q

What type of sugar residue is required in the oligosaccharide chain of gangliosides?
a) Glucose
b) Fructose
c) Galactose
d) Sialic acid

A

d) Sialic acid

61
Q

Which molecule is essential for the step-by-step addition of sugar residues to ceramide during ganglioside biosynthesis?
a) ATP
b) NADPH
c) Activated sugars
d) Phosphatidylcholine

A

c) Activated sugars

62
Q

What is the specific CMP derivative required for the addition of sialic acid residues to ceramide during ganglioside biosynthesis?
a) CMP-N-acetylneuraminate
b) CMP-N-glycolylneuraminate
c) CMP-glucose
d) CMP-sialic acid

A

a) CMP-N-acetylneuraminate

63
Q

How many monosaccharides are linked to ceramide in Ganglioside GM1?
a) Three
b) Four
c) Five
d) Six

A

c) Five

64
Q

What is the primary cause of Tay-Sachs disease?
a) Elevated cholesterol levels
b) Inability to degrade gangliosides
c) Deficiency in phospholipid synthesis
d) Excessive breakdown of lipids

A

b) Inability to degrade gangliosides

65
Q

How can Tay-Sachs disease be identified?
a) Magnetic resonance imaging (MRI)
b) Blood test
c) Genetic testing
d) Urine analysis

A

c) Genetic testing

66
Q

What is the main enzyme deficiency associated with Tay-Sachs disease?
a) Lipase
b) Phospholipase A2
c) β-N-acetylhexosaminidase
d) Sphingomyelinase

A

c) β-N-acetylhexosaminidase

67
Q

What is the role of phosphatidic acid phosphatase (PAP or lipin 1) in lipid metabolism?
a) It synthesizes phosphatidic acid from diacylglycerol.
b) It controls the synthesis of phospholipids relative to triacylglycerols.
c) It converts triacylglycerols into phospholipids.
d) It regulates the breakdown of cholesterol.

A

b) It controls the synthesis of phospholipids relative to triacylglycerols.

68
Q

What is produced when phosphatidate is dephosphorylated by phosphatidic acid phosphatase when its activity is high?
a) Phosphatidylcholine
b) Diacylglycerol (DAG)
c) Sphingomyelin
d) Phosphatidylserine

A

b) Diacylglycerol (DAG)

69
Q

How does phosphatidic acid phosphatase affect the utilization of phosphatidate when its activity is low?
a) It promotes the synthesis of triacylglycerols.
b) It inhibits the synthesis of phospholipids.
c) It acts as a signal molecule and cofactor.
d) It converts phosphatidate into cholesterol.

A

c) It acts as a signal molecule and cofactor.

biochem 2 (6 decks)

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