Ch. 21 Lehninger biochem test bank

1. Which of the following is not required in the synthesis of fatty acids?

A) Acetyl-CoA

B) Biotin

C) HCO3- (CO2)

D) Malonyl-CoA

E) NADH

E

2. Which of the following is not true of the reaction producing malonyl-CoA during fatty acid synthesis?

A) It is stimulated by citrate.

B) It requires 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.

B

3. 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).

D

4. Which one of the following statements best applies to 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 above

E

5. In comparing fatty acid biosynthesis with beta-oxidation of fatty acids, which of the following statements 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-beta-hydroxybutyrate is an intermediate in the synthetic path, not in the degradative path.

C) Fatty acid biosynthesis uses NADPH exclusively, whereas beta-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.

D

6. Which of the following is not true of the fatty acid synthase and the fatty acid beta-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.

E

7. The rate-limiting step in fatty acid synthesis is:

A) condensation of acetyl-CoA and malonyl-CoA.

B) formation of acetyl-CoA from acetate.

C) formation of malonyl-CoA from malonate and coenzyme A.

D) the reaction catalyzed by acetyl-CoA carboxylase.

E) the reduction of the acetoacetyl group to a beta-hydroxybutyryl group.

D

8. Which of the following 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.

E

9. Which of the following 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.

B

10. Which of these can be synthesized by plants but not by humans?

A) Linoleate [18:2(delta 9,12)]

B) Palmitate (16:0)

C) Phosphatidylcholine

D) Pyruvate

E) Stearate (18:0)

A

11. The enzyme system for adding double bonds to saturated fatty acids requires all of the following except:

A) a mixed-function oxidase.

B) ATP.

C) cytochrome b5.

D) molecular oxygen (O2).

E) NADPH.

B

12. Which of these statements about eicosanoid synthesis is true?

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

B) Arachidonate is derived mainly by 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

13. The biosynthesis of triacylglycerols from acetate occurs mainly in:

A) animals but not in plants.

B) humans after ingestion of excess carbohydrate.

C) humans with low carbohydrate intake.

D) plants but not in animals.

E) None of the above

B

14. The synthesis of both glycerophospholipids and triacylglycerols involves:

A) CDP-choline.

B) CDP-diacylglycerol.

C) phosphatidate phosphatase.

D) phosphatidic acid.

E) phosphoethanolamine.

D

15. Which of these statements about triacylglycerol synthesis is correct?

A) Humans can store more energy in glycogen than in triacylglycerols.

B) Insulin stimulates conversion of dietary carbohydrate into triacylglycerols.

C) It is not a hormone-sensitive process.

D) Mammals are unable to convert carbohydrates into triacylglycerols.

E) Phosphatidate is not on the pathway of triacylglycerol synthesis.

B

16. 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

B

17. All glycerol-containing phospholipids are synthesized from:

A) cardiolipin

B) ceramide.

C) gangliosides.

D) mevalonate.

E) phosphatidic acid.

E

18. In E. coli the synthesis of phosphatidylethanolamine directly involves:

A) acyl carrier protein.

B) biotin.

C) CDP-choline.

D) phosphatidylglycerol.

E) serine.

E

19. 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.

D

20. Palmitoyl-CoA, , is a direct precursor of:

A) cholesterol.

B) malonyl-CoA.

C) mevalonate

D) sphingosine.

E) squalene.

D

21. CDP-diglyceride is not involved in the biosynthesis of:

A) phosphatidylcholine.

B) phosphatidylethanolamine

C) phosphatidylglycerol.

D) phosphatidylserine.

E) sphingomyelin.

E

22. Which of the following 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.

C

23. Which of the following 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)

B

24. Cholesterol is synthesized from:

A) acetyl-CoA.

B) choline.

C) lipoic acid.

D) malate.

E) oxalate.

A

25. A 30-carbon precursor of the steroid nucleus is:

A) farnesyl pyrophosphate.

B) geranyl pyrophosphate.

C) isopentenyl pyrophosphate.

D) lysolecithin.

E) squalene.

E

26. Which of these statements 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.

C

27. Which of the following is derived from a sterol?

A) Bile salts

B) Gangliosides

C) Geraniol

D) Phosphatidylglycerol

E) Prostaglandins

A

28. Chylomicrons carry____in the______.

A) triacylglycerols; cell

B) triacylglycerols; blood

C) cholesterols; blood

D) fatty acids; blood

E) fatty acids; cell

B

29. Lipoprotein particles in human blood do not contain:

A) an apolipoprotein B isoform.

B) cholesterol.

C) cholesteryl esters.

D) lecithin.

E) triglycerides.

D

30. Which of the following contains the highest percentage of cholesteryl esters?

A) Chylomicrons

B) VLDL

C) LDL

D) HDL

E) None of the above contain any cholesteryl esters.

C

31. Which of the following 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.

D

32. Which of these statements 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 formation of cholesteryl esters.

D) Insulin stimulates HMG-CoA reductase.

E) Some metabolite or derivative of cholesterol inhibits HMG-CoA reductase.

A

33. Which of the following does not contribute to lowering the risk of atherosclerosis?

A) Statin drugs

B) HDL

C) Reverse cholesterol transport

D) ApoA-I

E) Foam cells

E

34. Which of these compounds is not synthesized by a pathway that includes isoprene precursors?

A) Natural rubber

B) Plastoquinone

C) Vitamin A

D) Vitamin B12

E) Vitamin K

E