Harper’s Illustrated Biochemistry, 29th Edition (2012)
The Answer Bank
Section I
1. D.
2. A.
3. D.
4. C.
5. A.
6. E.
7. B.
8. C.
9. A.
10. D.
11. E.
12. C.
13. B.
14. E.
15. D.
16. D.
17. E.
18. B.
19. B.
20. C.
21. D.
22. B.
23. B.
24. C.
Section II
1. E.
2. A.
3. E.
4. D. Thiamin diphosphate is a coenzyme of pyruvate dehydrogenase.
5. E. Xylulose, which is excreted in essential pentosuria, is a reducing compound and will therefore give a positive result with the alkaline copper reagent.
6. D. After 24 hours his liver and muscle glycogen reserves will be more or less completely depleted, and his plasma glucose will have fallen to about 3–4 mmol/L. There is no glycogen in the blood-stream. In response to low insulin and high glucagon, he will liberate free fatty acids from adipose tissue as a source of metabolic fuel for tissues that can metabolize fatty acids, so sparing glucose for brain and red blood cells.
7. C. As he becomes progressively more starved, his liver will synthesize ketone bodies as an additional fuel for muscle, which cannot meet all of its energy needs from fatty acid metabolism. This spares glucose for the brain and red blood cells.
8. D.
9. C.
10. C.
11. E.
12. D.
13. D.
14. A. Chylomicrons are synthesized in the intestinal mucosa, containing mainly triacylglycerol from dietary lipids, and peripheral tissues take up fatty acids by the action of extracellular lipoprotein lipase. Chylomicron remnants are cleared by the liver.
15. E. VLDL is secreted by the liver, containing both newly synthesized triacylglycerol and triacylglycerol from chylomicron remnants, and peripheral tissues take up fatty acids by the action of extracellular lipoprotein lipase.
16. D. Intermediate density lipoprotein results from the removal of triacylglycerol from very low-density lipoprotein by peripheral tissues. It then takes up cholesterol and proteins from high-density lipoprotein to become low-density lipoprotein, which is normally cleared by the liver.
17. A. Chylomicrons are synthesized in the intestinal mucosa, containing mainly triacylglycerol from dietary lipids, and peripheral tissues take up fatty acids by the action of extracellular lipoprotein lipase. Chylomicron remnants are cleared by the liver. Ketone bodies and non-esterified fatty acids are elevated in fasting, not after a meal.
18. E. Chylomicrons are mainly cleared by peripheral tissues within about 2 hours after a meal, and the chylomicron remnants are cleared by the liver. The residual triacylglycerol, plus triacylglycerol newly synthesized in the liver are secreted in very low-density lipoprotein as a source of fuel for peripheral tissues. Ketone bodies and non-esterified fatty acids are elevated in fasting, not after a meal.
19. D.
20. C.
21. C. Statins inhibit the activity of 3-hydroxy-3-methylglutaryl-CoA reductase, the enzyme that converts 3-hydroxy-3-methylglutaryl-CoA to mevalonate in the cholesterol biosynthesis pathway.
22. A.
23. B.
24. E.
25. D.
26. C.
27. B.
28. D.
29. C.
Section III
1. B. The insertion of seleneocysteine into a peptide occurs during translation, and is directed by a specific tRNA, tRNASec.
2. D. Phenylalanine hydroxylase does not convert tyrosine to phenylalanine.
3. E. Histamine.
4. B. Pyridoxal-dependent transamination is the first reaction in degradation of all the common amino acids except threonine, lysine, proline, and hydroxyproline.
5. A. Alanine.
6. A. The carbon skeleton of alanine contributes the most to hepatic gluconeogenesis.
7. B. ATP and ubiquitin participate in the degradation of nonmembrane-associated proteins and proteins with short half lives.
8. C. Clinical signs of metabolic disorders of the urea cycle include respiratory alkalosis, not acidosis.
9. E. Cytosolic fumarase and cytosolic malate dehydrogenase convert fumarase to oxaloacetate following a cytosolic reaction of the urea cycle.
10. B. Serine provides the thioethanol moiety of coenzyme A.
11. C. Decarboxylation of glutamate forms GABA.
12. E is not a hemoprotein. In cases of hemolytic anemia albumin can bind some metheme, but unlike the other proteins listed, albumin is not a hemoprotein.
13. B. Acute intermittent porphyria is due to mutations in the gene for uroporphyrin I synthase.
14. A. Bilirubin is a linear tetrapyrrole.
15. D. The severe jaundice, upper abdominal pain, and weight loss plus the lab results indicating an obstructive type of jaundice are consistent with cancer of the pancreas.
Section IV
1. D. β,γ-Methylene and β,γ-imino purine and pyrimidine triphosphates do not readily release the terminal phosphate by hydrolysis or by phosphoryl group transfer.
2. D.
3. E. Pseudouridine is excreted unchanged in human urine. Its presence there is not indicative of pathology.
4. A. Metabolic disorders are infrequently associated with defects in pyrimidine catabolism, which forms water-soluble products.
5. B.
6. D.
7. B.
8. C.
9. C.
10. D.
11. E.
12. B.
13. D.
14. D.
15. E.
16. A.
17. C.
18. B.
19. D.
20. B.
21. C.
22. A.
23. C.
24. A.
25. E.
26. B.
27. A.
28. E.
29. C.
30. A.
31. A.
32. C.
33. D.
34. E.
35. C.
36. B.
37. C.
38. E.
39. D.
40. D.
41. B.
42. A.
43. A.
44. E.
45. C.
46. A.
47. C.
48. D.
49. C.
50. B.
51. E.
52. C.
53. D.
54. A.
55. E.
56. A.
57. E.
58. C.
59. A.
60. D.
61. D.
62. E.
63. A.
64. C.
65. C.
66. E.
67. D.
Section V
1. B. Glycolipids are located on the outer leaflet.
2. A. Alpha-helices are major constituents of membrane proteins.
3. E. Insulin also increases glucose uptake in muscle.
4. A. Its action maintains the high intracellular concentration of potassium compared with sodium.
5. D.
6. B.
7. C.
8. B.
9. D.
10. A.
11. E.
12. B.
13. D.
14. E.
15. B.
16. C.
17. A.
18. C.
19. A.
20. B.
21. D.
22. A.
Section VI
1. C.
2. D.
3. E.
4. E.
5. C.
6. B.
7. C.
8. B.
9. E.
10. A.
11. A.
12. C.
13. E.
14. B.
15. B.
16. D.
17. A.
18. A. Superoxide dismutase serves to remove the superoxide radical.
19. A. Activation of macrophages leads to production of oxygen radicals.
20. B.
21. A. Glycosylation can occur at other sites, for example in the ER.
22. E. Importins are involved in import of proteins into the nucleus.
23. B. Some mammalian proteins are translocated post-translationally.
24. C. Ubiquitin is involved in protein degradation by proteasomes.
25. E. Furin converts proalbumin to albumin.
26. C.
27. A.
28. C. Some of the original sugars donated by the dolichol compound are subsequently removed and replaced by other sugars.
29. C. Glycation of hemoglobin occurs in normal individuals, but usually at a significantly lower level.
30. B. I-cell disease is due to mutations in a gene encoding a GlcNAc phosphotransferase.
31. D. Collagen contains cross-links.
32. C. Deletions in the elastin gene are responsible for many cases of Williams-Beuren syndrome.
33. B. Some cases of Ehlers-Danlos syndrome are not due to mutations affecting the genes encoding the various types of collagen.
34. B. Hyaluronic acid is not sulfated.
35. C. Hurler syndrome is due to a deficiency of α-L-iduronidase.
36. D. Achrondoplasia is due to mutations in the FGFR3 gene.
37. D. Tropomyosin is a constituent of the thin filament.
38. D. Myosin-ATP has a low affinity for actin, promoting release of actin from actin-myosin.
39. B. There is no evidence that the Na+ K+-ATPase is involved in MH.
40. B. Cardiac muscle contains the troponin system, and smooth muscle lacks it.
41. C. NO activates a guanylate cyclase, not adenylate cyclase.
42. E. Creatine phosphate is an important source of energy during the first few seconds.
43. A. Microfilaments do not contain myosin.
44. E. NFkB is a transcription factor, not a plasma protein.
45. C. Subjects with analbuminemia show only moderate edema; an increase in the plasma concentration of other proteins appears to compensate for the deficiency of albumin.
46. D. Transferrin is not degraded inside endosomes, but is instead re-used.
47. A. When intracellular levels of iron are high, the synthesis of ferritin is increased and that of TfR1 decreased.
48. D. Increased levels of red cell protoporphyrin are usually found in iron deficiency anemia. Note that tests D and E are not usually a standard part of the work-up of a patient with iron deficiency anemia.
49. B. A different copper-binding ATPase is involved in the causation of Menkes disease.
50. A. Amylase has nothing to do with amyloidosis.
51. A. All immunoglobulins are glycoproteins.
52. C. Bence-Jones proteins are light chains.
53. D.
54. D. Of the listed proteins, only factor II is a vitamin K-dependent coagulation factor.
55. D.
56. E. GPIIb-IIIa (integrin αIIbβ3) is not a G protein-coupled receptor.
57. A. Hemophilia A, being an X chromosome-linked disease, is very unlikely to occur in a female.
58. E. Mutations in the pyruvate kinase gene cause a hemolytic anemia, but not PNH.
59. D. The red blood cell lacks mitochondria and therefore does not possess the citric acid cycle.
60. B. In a hemolytic anemia levels of non-conjugated bilirubin are often elevated and levels of Hp decrease because of the release of hemoglobin into the plasma.
61. A. Pyruvate kinase is present in the cytosol.
62. B. Individuals of blood group AB have neither anti-A nor anti-B antibodies.
63. C. Lysozyme hydrolyzes the linkage between N-acetylmuramic acid and N-acetyl-D-glucosamine.
64. B. The enzyme contains cytochrome b558, not cytochrome P450.
65. D. Superoxide is not a product of the reaction catalyzed by cytochrome P450.
66. A. Hydroxylation is a phase 1 reaction.
67. A. GSH is a tripeptide containing glutamic acid, cysteine, and glycine.
68. D.
69. B.
70. E.
71. B.
72. B. Most chemical carcinogens interact covalently with DNA.
73. B. Certain DNA viruses are also known to be carcinogens.
74. E. Mutations in approximately 5-6 of these genes are thought to be necessary for carcinogenesis.
75. E. PDGF stimulates phospholipase C, not phospholipase A.
76. D. Binding of RB to E3F blocks progression of the cell from G1 to S phase.
77. C. Microsatellite instability is caused by abnormalities of mismatch repair.
78. E. Dichloroacetate inhibits pyruvate dehydrogenase kinase.
79. D. Angiogenin is an inhibitor of angiogenesis.
80. B. Cytochrome c is released from mitochondria.
81. E. Only about 1:10, 000 cancer cells may have the capacity to colonize.
82. C. Creatinine clearance is an estimate of the glomerular filtration rate (GFR). Therefore, measurement of creatinine clearance can help detect renal failure in its early stages. Measurement of blood urea and creatinine are not sensitive markers of renal function. Proteinuria is an important sign of kidney disease, but urinary protein may also be elevated in other pathological conditions and in physiological conditions such as pregnancy, prolonged standing, exposure to severe cold, strenuous exercise, etc. Urinary ammonia levels depend on a number of factors such as the acid-base status of the body and liver function. Urine volume depends on the amount of water consumed and loss of water due to sweating, etc.
83. A. The liver synthesizes most of the plasma proteins, including albumin. A low level of serum albumin is characteristically seen in chronic liver failure. Hypoalbuminemia may also be caused by loss of albumin in urine (e.g., nephrotic syndrome) or malnutrition (e.g., kwashiorkor). Measurement of total and conjugated bilirubin gives information on the ability of the liver to conjugate and excrete bilirubin. Alanine transaminase (ALT) is a marker of hepatocyte injury, and alkaline phosphatase (ALP) is a marker of biliary obstruction. Blood ammonia levels indicate the ability of the liver to detoxify ammonia.
84. C. An ideal substance, clearance of which is representative of the GFR, should have stable concentrations in the blood, be filtered freely at the glomerulus, and should neither be reabsorbed nor be secreted by the renal tubule. A substance that is metabolized by the body will not have stable blood levels and therefore is not suitable to measure the GFR.
85. B. TSH levels are usually greatly increased in primary hypothyroidism and suppressed or undetectable in primary hyperthyroidism. Since the large majority of cases of hypo-and hyperthyroidism are due to disorders primarily related to the thyroid gland, measurement of TSH has proven to be a cost-effective and clinically efficient strategy in the diagnosis of thyroid disorders. In addition, highly sensitive assays for TSH are now available commercially. Total thyroxine levels can be affected by changes in levels of thyroid-binding globulin, even in the euthyroid state. Free thyroxine and triiodothyronine measurements are technically difficult and expensive and are therefore not preferred as a first test in the assessment of thyroid function.
86. A. ADA deficiency only accounts for about 15% of cases of SCID.
87. D. APOE4 appears to decrease clearance of Aβ42.
88. C. The A subunit ADP-ribosylates the Gs subunit.
89. E. CEA is not an excellent test for detection of colorectal cancer because its sensitivity and specificity are relatively low.
90. B. The CF gene was discovered using “reverse genetics”, not because of a massive deletion on chromosome 7.
91. B. Acetone is also a ketone body.
92. A. CK-MM is the isozyme of creatine kinase that should be measured if DMD is suspected. Often measurement of total CK activity is used.
93. E. Ethanol is also metabolized by a microsomal cytochrome P450.
94. B. Uric acid is not produced from the metabolism of pyrimidines.
95. E. The preferred treatment is phlebotomy.
96. D. Levels of T4 are decreased in primary hypothyroidism.
97. D. High levels of cortisol favor muscle wasting.
98. B. Use of measurements of troponin T has replaced the use of CK-MB, partly because it is a more sensitive biochemical marker of damage to cardiac muscle.
99. C. α-MSH decreases appetite.
100. C. Osteomalacia is due to deficiency of vitamin D, not vitamin C.
101. A. XP involves mutations in the nucleotide excision DNA repair pathway.