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Biochemistry > Lipid Biosynthesis > Flashcards

Lipid Biosynthesis Flashcards

1
Q 
Which compound is NOT required in the synthesis of fatty acids?
A) acetyl-CoA
B) biotin
C) HCO3– (CO2)
D) malonyl-CoA
E) NADH
A

E) NADH

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2
Q

Which statement is NOT true of the reaction producing malonyl-CoA during fatty acid synthesis?
A) It is stimulated by citrate.
B) It requires an acyl carrier protein (ACP).
C) It requires CO2 (or bicarbonate).
D) One mole of ATP is converted to ADP + Pi for each malonyl-CoA synthesized.
E) The cofactor is biotin.

A

B) It requires an acyl carrier protein (ACP).

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3
Q

If malonyl-CoA is synthesized from 14CO2 and unlabeled acetyl-CoA, and the labeled malonate is then used for fatty acid synthesis, the final product (fatty acid) will have radioactive carbon in:
A) every C.
B) every even-numbered C-atom.
C) every odd-numbered C-atom.
D) no part of the molecule.
E) only the omega-carbon atom (farthest carbon from C-1).

A

D) no part of the molecule.

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4
Q

Which statement applies to the synthesis of fatty acids in E. coli extracts?
A) Acyl intermediates are thioesters of a low molecular weight protein called acyl carrier protein.
B) CO2 or HCO3– is essential.
C) Reducing equivalents are provided by NADPH.
D) The ultimate source of all the carbon atoms in the fatty acid product is acetyl-CoA.
E) All of the statements apply to the synthesis of fatty acids in E. coli extracts.

A

E) All of the statements apply to the synthesis of fatty acids in E. coli extracts.

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5
Q

In comparing fatty acid biosynthesis with  oxidation of fatty acids, which statement is INCORRECT?
A) A thioester derivative of crotonic acid (trans-2-butenoic acid) is an intermediate in the synthetic path, but not in the degradative path.
B) A thioester derivative of D--hydroxybutyrate is an intermediate in the synthetic path, not in the degradative path.
C) Fatty acid biosynthesis uses NADPH exclusively, whereas  oxidation uses NAD+ exclusively.
D) Fatty acid degradation is catalyzed by cytosolic enzymes; fatty acid synthesis by mitochondrial enzymes.
E) The condensation of two moles of acetyl-CoA in the presence of a crude extract is more rapid in bicarbonate buffer than in phosphate buffer at the same pH; the cleavage of acetoacetyl-CoA proceeds equally well in either buffer.

A

Fatty acid degradation is catalyzed by cytosolic enzymes; fatty acid synthesis by mitochondrial enzymes.

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6
Q

Which statement is NOT true of the fatty acid synthase and the fatty acid -oxidation systems?
A) A derivative of the vitamin pantothenic acid is involved.
B) Acyl-CoA derivatives are intermediates.
C) Double bonds are oxidized or reduced by pyridine nucleotide coenzymes.
D) The processes occur in different cellular compartments.
E) The processes occur in the mitochondrial matrix.

A

E) The processes occur in the mitochondrial matrix.

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7
Q

Which statement is NOT true of the fatty acid elongation system of vertebrate cells?
A) It involves the same four-step sequence seen in the fatty acid synthase complex.
B) It is located in the smooth endoplasmic reticulum.
C) It produces stearoyl-CoA by the extension of palmitoyl-CoA.
D) It uses malonyl-CoA as a substrate.
E) The immediate precursor of the added carbons is acetyl-CoA.

A

E) The immediate precursor of the added carbons is acetyl-CoA.

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8
Q

Which statement is NOT true about precursors required for fatty acid synthesis in animal cells?
A) NADPH is produced in the cytosol by the pentose phosphate pathway.
B) NADPH is produced in the nucleus by malic enzyme.
C) Acetyl-CoA is transported out of the mitochondrion via the citrate shuttle.
D) CoA is not transported across the mitochondrial membrane.
E) Malonyl-CoA is formed in the cytosol.

A

B) NADPH is produced in the nucleus by malic enzyme.

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9
Q 
The enzyme system for adding double bonds to saturated fatty acids does NOT require:
A) a mixed-function oxidase.
B) ATP.
C) cytochrome b5.
D) molecular oxygen (O2).
E) NADPH.
A

B) ATP.

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10
Q

Which statement about eicosanoid synthesis is TRUE?
A) An early step in the path to thromboxanes is blocked by ibuprofen.
B) Arachidonate is derived mainly by the hydrolysis of triacylglycerols.
C) Aspirin acts by blocking the synthesis of arachidonate.
D) Plants can synthesize leukotrienes, but humans cannot.
E) Thromboxanes are produced from arachidonate via the “linear” path.

A

A) An early step in the path to thromboxanes is blocked by ibuprofen.

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11
Q

The biosynthesis of triacylglycerols from acetate occurs mainly in:
A) animals but not in plants.
B) humans after the ingestion of excess carbohydrates.
C) humans with low carbohydrate intake.
D) plants but not in animals.
E) None of the answers is correct.

A

B) humans after the ingestion of excess carbohydrates.

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12
Q 
The synthesis of both glycerophospholipids and triacylglycerols involves:
A) CDP-choline.
B) CDP-diacylglycerol.
C) phosphatidate phosphatase.
D) phosphatidic acid.
E) phosphoethanolamine.
A

D) phosphatidic acid.

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13
Q

A strategy that is NOT employed in the synthesis of phospholipids is:
A) condensation of CDP-alcohol with diacylglycerol.
B) condensation of CDP-diacylglycerol with alcohol.
C) condensation of CDP-diacylglycerol with CDP-alcohol.
D) exchange of free alcohol with head group alcohol of phospholipid.
E) remodeling of head group alcohols by chemical modification

A

B) condensation of CDP-diacylglycerol with alcohol.

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14
Q 
All glycerol-containing phospholipids are synthesized from:
A) cardiolipin
B) ceramide.
C) gangliosides.
D) mevalonate.
E) phosphatidic acid.
A

E) phosphatidic acid.

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15
Q 
In E. coli the synthesis of phosphatidylethanolamine directly involves:
A) acyl carrier protein.
B) biotin.
C) CDP-choline.
D) phosphatidylglycerol.
E) serine.
A

E) serine.

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16
Q 
In the synthesis of phosphatidylcholine from phosphatidylethanolamine, the methyl group donor is:
A) a tetrahydrofolate derivative.
B) choline.
C) methanol.
D) S-adenosylmethionine (adoMet).
E) serine.
A

D) S-adenosylmethionine (adoMet).

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17
Q 
Palmitoyl-CoA, is a direct precursor of: 
A) cholesterol.
B) malonyl-CoA. 
C) mevalonate
D) sphingosine.
E) squalene.
A

D) sphingosine.

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18
Q 
CDP-diglyceride is NOT involved in the biosynthesis of: A) phosphatidylcholine.
B) phosphatidylethanolamine
C) phosphatidylglycerol.
D) phosphatidylserine.
E) sphingomyelin.
A

E) sphingomyelin.

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19
Q

Which statement is TRUE of sphingolipid synthesis?
A) All of the carbon atoms of palmitate and serine are incorporated into sphingosine.
B) CDP-sphingosine is the activated intermediate.
C) CO2 is produced during the synthesis of ceramide from palmitate and serine.
D) Glucose 6-phosphate is the direct precursor of the glucose in cerebrosides.
E) Phosphatidic acid is a key intermediate in the pathway.

A

C) CO2 is produced during the synthesis of ceramide from palmitate and serine.

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20
Q

Which compound is NOT an intermediate in the synthesis of lanosterol from acetyl- CoA?
A) isopentenyl pyrophosphate
B) malonyl-CoA
C) mevalonate
D) squalene
E) beta-hydroxy-beta-methylglutaryl-CoA (HMG-CoA)

A

B) malonyl-CoA

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21
Q 
A 30-carbon precursor of the steroid nucleus is:
A) farnesyl pyrophosphate.
B) geranyl pyrophosphate.
C) isopentenyl pyrophosphate.
D) lysolecithin.
E) squalene.
A

E) squalene.

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22
Q

Which statement about cholesterol synthesis is TRUE?
A) Cholesterol is the only known natural product whose biosynthesis involves
isoprene units.
B) Only half of the carbon atoms of cholesterol are derived from acetate.
C) Squalene synthesis from farnesyl pyrophosphate results in the release of two moles of PPi for each mole of squalene formed.
D) The activated intermediates in the pathway are CDP-derivatives.
E) The condensation of two five-carbon units to yield geranyl pyrophosphate occurs in a “head-to-head” fashion.

A

C) Squalene synthesis from farnesyl pyrophosphate results in the release of two moles of PPi for each mole of squalene formed.

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23
Q 
Which compound(s) is/are derived from a sterol?
A) bile salts
B) gangliosides
C) geraniol
D) phosphatidylglycerol
E) prostaglandins
A

A) bile salts

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24
Q 
Chylomicrons carry \_\_\_\_\_ in the \_\_\_\_\_.
A) triacylglycerols; cell
B) triacylglycerols; blood
C) cholesterols; blood
D) fatty acids; blood
E) fatty acids; cell
A

B) triacylglycerols; blood

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25
Q 
Lipoprotein particles in human blood do NOT contain:
A) an apolipoprotein B isoform.
B) cholesterol.
C) cholesteryl esters.
D) lecithin.
E) triglycerides.
A

D) lecithin.

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26
Q

Which compound(s) contain(s) the HIGHEST percentage of cholesteryl esters?
A) chylomicrons
B) VLDL
C) LDL
D) HDL
E) None of these compounds contain any cholesteryl esters.

A

C) LDL

27
Q

Which statement is NOT a step in the uptake of cholesterol from the bloodstream into cells?
A) LDL containing ApoB-100 is recognized by the LDL receptor.
B) LDL bound to the LDL receptor leads to endocytosis of the complex.
C) The cholesteryl esters in the LDL are hydrolyzed to release free cholesterol.
D) The internalized receptor is degraded.
E) The ApoB-100 protein is degraded.

A

D) The internalized receptor is degraded.

28
Q

Which statement about the regulation of cholesterol synthesis is NOT true?
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 the formation of cholesteryl esters.
D) Insulin stimulates HMG-CoA reductase.
E) Some metabolites or derivative of cholesterol inhibits HMG-CoA reductase.

A

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

29
Q 
Which factor does NOT contribute to lowering the risk of atherosclerosis?
A) statin drugs
B) HDL
C) reverse cholesterol transport
D) ApoA-I
E) foam cells
A

E) foam cells

30
Q 
Which compound is NOT synthesized by a pathway that includes isoprene precursors?
A) natural rubber
B) plastoquinone
C) vitamin A
D) vitamin B12
E) vitamin K
A

E) vitamin K

31
Q

Which statement is FALSE concerning acetyl-CoA carboxylase?
A) It catalyzes the rate-limiting step in fatty acid synthesis.
B) This enzyme is inhibited by palmitate in mammals.
C) This enzyme is allosterically activated by citrate in mammals.
D) In mammals, this enzyme is inactivated under conditions when glycolysis is active.
E) This enzyme is classified as a ligase.

A

D) In mammals, this enzyme is inactivated under conditions when glycolysis is active.

32
Q

What cofactor is required for acetyl-CoA carboxylase activity?
A) NADPH
B) thiamine pyrophosphate
C) lipoamide
D) biotin
E) both thiamine pyrophosphate and lipoamide

A

C) lipoamide

33
Q

Synthesis of malonyl-CoA from acetyl-CoA is MOST similar to what other reaction?
A) conversion of malate into fumarate
B) conversion of pyruvate into acetyl-CoA
C) conversion of phosphoenolpyruvate into 2-phosphoglycerate
D) conversion of glutamate into -ketoglutarate
E) conversion of pyruvate into oxaloacetate

A

E) conversion of pyruvate into oxaloacetate

34
Q

Which statement does NOT describe a difference between fatty acid synthase I (FAS I) and fatty acid synthase II (FAS II)?
A) FAS I is found in fungi, while FAS II is found in plants.
B) FAS I has no quaternary structure, while FAS II does.
C) Intermediates are not released in FAS I catalysis but are released in FAS II catalysis.
D) A single lipid product is produced from FAS I while multiple products may be produced by FAS II.
E) All of these statements describe differences between FAS I and FAS II.

A

B) FAS I has no quaternary structure, while FAS II does.

35
Q 
Which enzyme activity is NOT part of FAS II?
A) a dehydratase
B) a thioesterase
C) a carboxylase
D) a transferase
E) a reductase
A

C) a carboxylase

36
Q

Which statement is FALSE regarding acyl-carrier protein (ACP)?
A) ACP is transiently attached to malonyl-CoA during fatty acid elongation.
B) ACP contains a pantothenate-derived prosthetic group.
C) ACP carries reaction intermediates from one active site to the next in fatty acid synthesis.
D) ACP associates as a separate polypeptide with fatty acid synthase I in vertebrates.
E) Fatty acyl chains on ACP are transferred to a cysteine on -ketoacyl-ACP synthase during fatty acid synthesis.

A

D) ACP associates as a separate polypeptide with fatty acid synthase I in vertebrates.

37
Q 
After four rounds of fatty acid synthase activity, what size is the fatty acyl intermediate?
A) 4 carbons long
B) 5 carbons long
C) 8 carbons long
D) 9 carbons long
E) 10 carbons long
A

E) 10 carbons long

38
Q 
Which compound is NOT an intermediate in transfer of acetyl groups from mitochondria to the cytosol?
A) citrate
B) malate
C) oxaloacetate D) fumarate
E) pyruvate
A

D) fumarate

39
Q

In one cycle of acetyl transfer from mitochondria to the cytosol via citrate, what other net change occurs?
A) net conversion of NADH to NADPH in the cytosol
B) net export of coenzyme A from mitochondria
C) net import of NADH from the cytosol into mitochondria
D) net consumption of 1 ATP
E) overall conversion of oxaloacetate into pyruvate

A

A) net conversion of NADH to NADPH in the cytosol

40
Q 
What effect will the presence of citrate have on the activity of acetyl-CoA carboxylase in mammals?
A) no effect
B) decreased K0.5
C) increased K0.5
D) decreased Vmax
E) increased Vmax
A

E) increased Vmax

41
Q 
Conversion of saturated fatty acyl chains to unsaturated fatty acyl chains by fatty acyl- CoA desaturase is accompanied by what other net change?
A) reduction of NAD+ to NADH
B) reduction of NADP+ to NADPH
C) reduction of O2 to H2O
D) reduction of oxaloacetate to malate
E) reduction of FAD to FADH2
A

C) reduction of O2 to H2O

42
Q 
What type of inhibitor is acetylsalicylic acid for COX-2?
A) a competitive inhibitor
B) a noncompetitive inhibitor
C) an uncompetitive inhibitor
D) a mixed inhibitor
E) None of the answers is correct.
A

E) None of the answers is correct.

43
Q 
Which compound is NOT a substrate or product of lipin?
A) diacylglycerol
B) phosphatidic acid
C) water
D) lysophosphatidic acid
E) inorganic phosphate
A

D) lysophosphatidic acid

44
Q 
Synthesis of a triglyceride from three fatty acids and glycerol costs how many ATP equivalents?
A) three 
B) four 
C) five 
D) six 
E) seven
A

E) seven

45
Q

Which statement is FALSE regarding the conversion of dihydroxyacetone phosphate (DHAP) to glycerol-3-phosphate in the cytosol of adipose cells?
A) The reaction reduces C1 of DHAP.
B) This reaction creates a new chiral center.
C) This reaction requires the cofactor NADH.
D) This reaction is catalyzed by glycerol-3-phosphate dehydrogenase.
E) This reaction is catalyzed by an oxidoreductase.

A

A) The reaction reduces C1 of DHAP.

46
Q

Which statement is FALSE regarding the formation of phosphatidylserine involving CTP activated intermediates in E. coli?
A) The nucleophile is the OH at C3 of diacylglyceol.
B) CMP acts as a leaving group.
C) This is a nucleophilic substitution reaction.
D) A product of the reaction is a phosphodiester.
E) Loss of a phosphoanhydride makes this reaction energetically favorable.

A

A) The nucleophile is the OH at C3 of diacylglyceol.

47
Q 
Synthesis of cardiolipin from phosphatidate, CTP, and glycerol-3-phosphate in E. coli consumes how many phosphoanhydride bonds?
A) zero
B) one
C) two 
D) three 
E) four
A

E) four

48
Q 
What is the source of the polar headgroup in the formation of sphingomyelin? A) CDP-choline
B) phosphocholine
C) cardiolipin
D) phosphoserine
E) phosphatidylcholine
A

E) phosphatidylcholine

49
Q

Biosynthesis of mammalian membrane phospholipids takes place in what cellular locations?
A) the lysosomal membrane and the plasma membrane
B) the plasma membrane and the smooth endoplasmic reticulum
C) the inner mitochondrial membrane and the plasma membrane
D) the smooth endoplasmic reticulum and the inner mitochondrial membrane
E) the inner mitochondrial membrane and the lysosomal membrane

A

D) the smooth endoplasmic reticulum and the inner mitochondrial membrane

50
Q 
Synthesis of phosphatidyl-choline from choline and diacylglycerol in mammals requires which nucleotides as other substrates?
A) ATP and UTP
B) CTP and UTP
C) ATP and CTP
D) CTP only
E) ATP, UTP, and CTP
A

C) ATP and CTP

51
Q

Synthesis of sphingosine from palmitoyl-CoA and serine requires which enzymatic class?
A) transferases
B) oxidoreductases
C) hydrolases
D) ligases
E) All of these enzymatic classes are required.

A

D) ligases

52
Q 
Conversion of phosphatidylserine into phosphatidylethanolamine requires what chemical process?
A) dehydration
B) methylation
C) dehydrogenation 
D) reduction
E) decarboxylation
A

E) decarboxylation

53
Q

Which list ranks the compounds in order from the fewest to the greatest number of carbon atoms?
A) acetate, cholesterol, mevalonate, squalene
B) acetate, mevalonate, squalene, cholesterol
C) mevalonate, cholesterol, squalene, acetate
D) acetate, squalene, mevalonate, cholesterol
E) acetate, mevalonate, cholesterol, squalene

A

E) acetate, mevalonate, cholesterol, squalene

54
Q 
How many phosphoanhydride bonds (net) are consumed in the conversion of mevalonate into the activated isoprene compound dimethylallyl pyrophosphate? A) zero
B) one
C) two 
D) three 
E) four
A

D) three

55
Q 
What is the net cost, in terms of high energy molecules, in the synthesis of squalene from acetyl-CoA?
A) 2 NADPH and 3 ATP
B) 6 NADPH and 9 ATP
C) 6 NAPDH and 18 ATP
D) 12 NADPH and 18 ATP
E) 13 NADPH and 18 ATP
A

E) 13 NADPH and 18 ATP

56
Q

Which statement is FALSE concerning bile salts?
A) They are more amphipathic than cholesterol.
B) They are secreted in response to fat ingestion.
C) They are synthesized in the gall bladder.
D) They are sterol derivatives.
E) They typically carry a negative charge

A

C) They are synthesized in the gall bladder.

57
Q 
Which apolipoprotein is found in chylomicrons but not in other lipoproteins? A) ApoB-48
B) ApoB-100 
C) ApoC-II 
D) ApoC-III 
E) ApoE
A

A) ApoB-48

58
Q 
Reverse cholesterol transport is primarily associated with which lipoprotein? A) chylomicrons
B) VLDL
C) IDL
D) LDL 
E) HDL
A

E) HDL

59
Q

Conversion of VLDL into LDL is associated with what changes?
A) depletion of cholesteryl-esters
B) enrichment of the apolipoprotein ApoB-100
C) an increase in particle diameter
D) a decrease in the protein:lipid ratio
E) ApoE-mediated receptor interactions

A

B) enrichment of the apolipoprotein ApoB-100

60
Q 
Which apolipoprotein is recognized by the LDL receptor? 
A) ApoB-100
B) ApoC-I 
C) ApoC-II 
D) ApoD 
E) ApoE
A

E) ApoE

61
Q 
Which lipoproteins do NOT originate from the liver?
A) chylomicrons and VLDL
B) VLDL and HDL
C) LDL and HDL
D) chylomicrons and HDL
E) VLDL and LDL
A

D) chylomicrons and HDL

62
Q

Which protein is NOT typically found in HDL?
A) lecithin cholesterol acyl transferase (LCAT)
B) ApoE
C) ApoH
D) ApoC-I
E) ApoD

A

C) ApoH

63
Q

What statement is FALSE regarding the differences between chylomicrons and VLDL?
A) These two lipoproteins originate in different tissues.
B) Chylomicrons have a lower density than VLDL.
C) Chylomicrons contain ApoB-48 while VLDL contains ApoB-100.
D) Chylomicrons contain a lower percentage of protein compared to VLDL.
E) Chylomicrons contain an overall lower triacylglycerol percentage than VLDL.

A

E) Chylomicrons contain an overall lower triacylglycerol percentage than VLDL.

64
Q

What statement is FALSE regarding the regulation of HMG-CoA reductase?
A) HMG-CoA reductase is inhibited by phosphorylation.
B) Elevated levels of ATP will inhibit HMG-CoA reductase.
C) Elevated blood glucose will increase the activity of HMG-CoA reductase.
D) Statins act as competitive inhibitors for this enzyme.
E) Low cellular concentrations of cholesterol will increase expression of this enzyme and the LDL receptor.

A

B) Elevated levels of ATP will inhibit HMG-CoA reductase.

Biochemistry (6 decks)

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