Harper’s Illustrated Biochemistry, 29th Edition (2012)
SECTION VI. Special Topics
Exam Questions
Section VI
1. The glycemic index of a food is a way of assessing how rapidly the carbohydrate in that food is digested and absorbed Which of the following is the best definition of glycemic index?
A. The decrease in the blood concentration of glucagon after consuming the food compared with an equivalent amount of white bread.
B. The increase in the blood concentration of glucose after consuming the food.
C. The increase in the blood concentration of glucose after consuming the food compared with an equivalent amount of white bread.
D. The increase in the blood concentration of insulin after consuming the food.
E. The increase in the blood concentration of insulin after consuming the food compared with an equivalent amount of white bread.
2. Which of the following will have the lowest glycemic index?
A. A baked apple
B. A baked potato
C. An uncooked apple
D. An uncooked potato
E. Apple juice
3. Which of the following will have the highest glycemic index?
A. A baked apple
B. A baked potato
C. An uncooked apple
D. An uncooked potato
E. Apple juice
4. Which of the following best describes the digestion and absorption of dietary triacylglycerol?
A. Absorption of partially hydrolysed lipids in lipid micelles that are then incorporated directly into chylomicrons.
B. Absorption of triacylglycerol in lipid micelles that is then incorporated into chylomicrons.
C. Complete hydrolysis to free fatty acids and glycerol in the intestinal lumen.
D. Hydrolysis to free fatty acids and monoacylglycerol in the intestinal lumen followed by complete hydrolysis of monoacylglycerol in mucosal cells, and re-esterification to triacylglycerol matching the pattern of dietary triacylglycerol.
E. Hydrolysis to free fatty acids and monoacylglycerol in the intestinal lumen followed by partial hydrolysis of monoacylglycerol in mucosal cells and re-esterification to triacylglycerol with a different pattern of fatty acids from that in the dietary triacylglycerol.
5. Plant sterols and stanols inhibit the absorption of cholesterol from the gastro-intestinal tract. Which of the following best describes how they act?
A. They are incorporated into chylomicrons in place of cholesterol.
B. They compete with cholesterol for esterification in the intestinal lumen, so that less cholesterol is esterified.
C. They compete with cholesterol for esterification in the mucosal cell, and unesterified cholesterol is actively transported out of the cell into the intestinal lumen.
D. They compete with cholesterol for esterification in the mucosal cell, and unesterified cholesterol is not incorporated into chylomicrons.
E. They displace cholesterol from lipid micelles, so that it is not available for absorption.
6. Which one of following statements about energy metabolism is CORRECT?
A. Adipose tissue does not contribute to basal metabolic rate (BMR).
B. Physical activity level (PAL) is the sum of physical activity ratios for different activities throughout the day, multiplied by the time spent in each activity, expressed as a multiple of BMR.
C. Physical activity ratio (PAR) is the energy cost of physical activity throughout the day.
D. Resting metabolic rate (RMR) is the energy expenditure of the body when asleep.
E. The energy cost of physical activity can be determined by measuring respiratory quotient (RQ) during the activity.
7. Which one of following statements about nitrogen balance is CORRECT?
A. If the intake of protein is greater than requirements, there will always be positive nitrogen balance.
B. In nitrogen equilibrium the excretion of nitrogenous metabolites is greater than the dietary intake of nitrogenous compounds.
C. In positive nitrogen balance the excretion of nitrogenous metabolites is less than the dietary intake of nitrogenous compounds.
D. Nitrogen balance is the ratio of intake of nitrogenous compounds/output of nitrogenous metabolites from the body.
E. Positive nitrogen balance means that there is a net loss of protein from the body.
8. Which of the following vitamins provides the cofactor for reduction reactions in fatty acid synthesis?
A. Folate
B. Niacin
C. Riboflavin
D. Thiamin
E. Vitamin B6
9. Which of the following vitamins provides the cofactor for transamination of amino acids?
A. Folate
B. Niacin
C. Riboflavin
D. Thiamin
E. Vitamin B6
10. Which of the following vitamins provides the cofactor for transfer of one-carbon units?
A. Folate
B. Niacin
C. Riboflavin
D. Thiamin
E. Vitamin B6
11. Which of the following vitamins is essential for fatty acid synthesis?
A. Biotin
B. Folate
C. Vitamin B6
D. Vitamin B12
E. Vitamin C
12. Which one of these vitamins is involved in calcium homeostasis?
A. Vitamin B12
B. Vitamin B6
C. Vitamin D
D. Vitamin E
E. Vitamin K
13. Which one of these vitamins is involved in blood clotting?
A. Vitamin B6
B. Vitamin B12
C. Vitamin D
D. Vitamin E
E. Vitamin K
14. Deficiency of which one of these vitamins may lead to megaloblastic anemia?
A. Vitamin B6
B. Vitamin B12
C. Vitamin D
D. Vitamin E
E. Vitamin K
15. Which one of these vitamins may mask the anemia of vitamin B12deficiency?
A. Biotin
B. Folate
C. Riboflavin
D. Thiamin
E. Vitamin B6
16. Deficiency of which one of these vitamins may lead to hemolytic anemia?
A. Vitamin B6
B. Vitamin B12
C. Vitamin D
D. Vitamin E
E. Vitamin K
17. Deficiency of which one of these vitamins is a major cause of blindness worldwide?
A. Vitamin A
B. Vitamin B12
C. Vitamin B6
D. Vitamin D
E. Vitamin K
18. Which one of the following is NOT a source of oxygen radicals?
A. Action of superoxide dismutase
B. Activation of macrophages
C. Non-enzymic reactions of transition metal ions
D. Reaction of β-carotene with oxygen
E. Ultraviolet radiation
19. Which one of the following is NOT the result of oxygen radical action?
A. Activation of macrophages
B. Modification of bases in DNA
C. Oxidation of amino acids in apoproteins of LDL
D. Peroxidation of unsaturated fatty acids in membranes
E. Strand breaks in DNA
20. Epidemiological evidence and laboratory studies suggest that antioxidant nutrients such as vitamins C and E and β-carotene are protective against atherosclerosis and some cancers. However, intervention trials with antioxidant supplements have given disappointing results, and in many cases there have been more deaths from coronary heart disease and cancer in the intervention group than in those receiving placebo. Which of the following best explains this paradox?
A. Antioxidants are lipid-soluble and therefore cannot act in the cytosol or extracellular fluid.
B. Antioxidants form stable radicals that penetrate deeper into tissues, causing more damage.
C. Antioxidants form stable radicals that quench the radical chain reaction.
D. The doses of antioxidant have generally been too low for any beneficial effects to be seen.
E. The intervention trials have generally been of too short a duration for any beneficial effects to be seen.
21. Select the one FALSE statement:
A. Glycosylation occurs solely in the Golgi apparatus.
B. There are no structural differences between free and bound ribosomes.
C. Proteins destined for the plasma membrane and for secretion are generally synthesized on membrane-bound polyribosomes.
D. The proton-motive force across the inner mitochondrial membrane is derived from the electric potential and the pH gradient.
E. Certain pancreatic proteins destined for export are carried in secretory vesicles.
22. Select the one FALSE statement:
A. The great majority of mitochondrial proteins are encoded by the nuclear genome.
B. Ran proteins, like ARF and Ras proteins, are monomeric GTPases.
C. One cause of Refsum disease is mutations in genes encoding peroxisomal proteins.
D. Peroxisomal proteins are synthesized on cytosolic polyribosomes.
E. Import of proteins into mitochondria involves proteins known as importins.
23. Select the one FALSE statement:
A. N-terminal signal peptides directing nascent proteins to the ER membrane contain a hydrophobic sequence.
B. Post-translational translocation of proteins to the ER does not occur in mammalian species.
C. The SRP contains one RNA species.
D. N-glycosylation is catalyzed by oligosaccharide:protein transferase.
E. Type I membrane proteins have their N-termini facing the lumen of the ER.
24. Select the one FALSE statement:
A. Chaperones often exhibit ATPase activity.
B. Protein disulfide isomerase and peptidyl prolyl isomerase are enzymes involved in helping proteins fold properly.
C. Ubiquitin is a small protein involved in protein degradation by lysosomes.
D. Mitochondria contain chaperones.
E. Retrotranslocation across the ER membrane is involved in helping dispose of misfolded proteins.
25. Select the one FALSE statement:
A. Rab is a small GTPase involved in vesicle targeting.
B. COPII vesicles are involved in anterograde transport of cargo from the ER to the ERGIC or Golgi apparatus.
C. Brefeldin A prevents GTP binding to ARF, and thus inhibits formation of COP I vesicles.
D. Botulinum toxin B acts by cleaving synaptobrevin, inhibiting release of acetylcholine at the neuromuscular junction.
E. Furin converts preproalbumin to proalbumin.
26. All of the following are glycoproteins EXCEPT:
A. Collagen
B. TSH
C. Albumin
D. IgG
E. Transferrin
27. All of the following sugars are found in glycoproteins EXCEPT:
A. Fructose
B. Fucose
C. Galactose
D. Mannose
E. Xylose
28. Select the one FALSE statement:
A. Mucins contain predominantly O-linked glycans.
B. O-linked sugar chains are built up by the stepwise donation of sugars from nucleotide-sugars.
C. Dolichol-pyrophosphate-oligosaccharide donates all of the sugars found in mature N-linked glycoproteins.
D. N-acetylneuraminic acid is commonly found at the termini of N-linked sugar chains.
E. Calnexin retains partly folded or misfolded proteins in the ER until proper folding has occurred.
29. Select the one FALSE statement:
A. Glucose can attach to proteins via a non-enzymic reaction to form a Schiff base.
B. Abnormal glycation end-products are thought to play a role in the tissue damage that occurs in diabetes mellitus.
C. Glycation of hemoglobin only occurs in individuals with diabetes mellitus.
D. Abnormal glypiation is involved in the causation of paroxysmal nocturnal hemoglobinuria.
E. The attachment of P falciparum to some human cells is mediated by a GPI structure on the surface of the parasite.
30. Select the one FALSE statement:
A. The initial attachment of neutrophils to endothelial cells of small blood vessels in acute inflammation involves interactions between L-selectin and endothelial cell glycoproteins.
B. I-cell disease is due to mutations in the gene encoding a GalNAc phosphotransferase.
C. The binding of avian influenza virus to human cells involves an interaction between hemagglutinin and cell surface N-acetylneuraminic acid.
D. HIV-1 attaches to human cells via a glycoprotein (gp120) present on its surface.
E. Hpylori attaches to human cells via an interaction between adhesin and cell surface glycans.
31. Select the one FALSE statement:
A. Collagen has a triple helical structure, forming a right-hand superhelix.
B. Proline and hydroxyproline confer rigidity on collagen.
C. Collagen contains one or more O-glycosidic linkages.
D. Collagen lacks cross-links.
E. Deficiency of vitamin C impairs the action of prolyl and lysyl hydroxylases.
32. Select the one FALSE statement:
A. Elastin contains hydroxyproline, but not hydroxylysine.
B. Elastin contains cross-links formed by desmosines.
C. No genetic diseases due to abnormalities of elastin have as yet been identified.
D. Unlike collagen, there is only one gene encoding elastin.
E. Elastin does not contain any sugar molecules.
33. Select the one FALSE statement:
A. Marfan syndrome is due to mutations in the gene encoding fibrillin-1, a major constituent of microfibrils.
B. All cases of Ehlers-Danlos syndrome are due to mutations affecting the genes encoding the various types of collagen.
C. Laminin is found in renal glomeruli along with entactin, type IV collagen, and heparin or heparan sulfate.
D. Mutations affecting type IV collagen can cause serious renal disease.
E. Mutations in the collagen 1A1 gene can cause osteogenesis imperfecta.
34. Select the one FALSE statement:
A. Most but not all GAGs contain an amino sugar and a uronic acid.
B. All GAGs are sulfated.
C. GAGs are built up the actions of glycosyltransferases using sugars donated by nucleotide-sugars.
D. Glucuronic acid can be converted to iduronic acid by an epimerase.
E. The proteoglycan aggrecan contains hyaluronic acid, keratan sulfate, and chondroitin sulfate.
35. A male infant is failing to thrive and, on examination, is noted to have hepatomegaly and splenomegaly, among other findings. Urinalysis reveals the presence of both dermatan sulfate and heparan sulfate. You suspect the patient has Hurler syndrome. From the following list, select the enzyme that you would wish to have assayed to support your diagnosis:
A. β-Glucuronidase.
B. β-Galactosidase.
C. α-L-Iduronidase
D. α-N-Acetylglucosaminidase
E. Neuraminidase
36. You see a child in clinic who is well below average height. You note that the child has short limbs, normal trunk size, macrocephaly, and a variety of other skeletal abnormalities. You suspect that the child has achrondoplasia. Select from the following list the test that would best confirm your diagnosis:
A. Measurement of growth hormone
B. Assays for enzymes involved in the metabolism of GAGs
C. Tests for urinary mucopolysaccharides
D. Gene tests for abnormalities of the fibroblast growth factor receptor 3
E. Gene tests for abnormalities of growth hormone
37. Regarding muscle proteins, select the one FALSE statement:
A. Actin is a major constituent of thin filaments.
B. F-actin can polymerize under physiological condition to G-actin.
C. The head region of myosin-II, the major constituent of thick filaments, has ATPase activity.
D. Tropomyosin is an important constituent of the thick filament.
E. F-actin greatly promotes the release of ADP and Pi from myosin ATPase.
38. Regarding the process of muscle contraction, select the one FALSE statement:
A. Binding of Ca2+ to troponin C uncovers the myosin binding sites of actin, permitting actin and myosin to interact.
B. Release of Pi from the actin-myosin-ADP-Pi complex initiates the power stroke.
C. Release of ADP from the actin-myosin-ADP complex is accompanied by a large conformational change in the head of myosin in relation to its tail.
D. Myosin-ATP has a high affinity for actin.
E. If levels of ATP are low, rigor mortis can ensue because of failure of release of actin from the actin-myosin complex.
39. During anesthesia using halothane you notice that your patient’s temperature is rising rapidly and you suspect malignant hyperthermia (MH). Select the one FALSE statement:
A. MH can be due to mutations affecting the Ca2+ release channel (RYR).
B. MH can be due to mutations affecting the Na+ K+-ATPase.
C. MH can also be due to mutations affecting the dihydropyridine receptor, a voltage-gated slow K type Ca2+ channel.
D. A high intracellular concentration of Ca2+, causing rigidity of muscles, is found in MH.
E. Appropriate treatment of MH is i.v. administration of dantrolene to inhibit release of Ca from the SR into the cytosol.
40. Concerning different types of muscle, select the one FALSE statement:
A. Skeletal muscle lacks caldesmon.
B. Cardiac muscle lacks the troponin system.
C. The concentration of extracellular Ca2+ is important for the contraction of cardiac and smooth muscle.
D. Smooth muscle exhibits slow cycling of cross-bridges, allowing prolonged contraction.
E. Skeletal, cardiac, and smooth muscles all contain the actin-myosin system.
41. Select the one FALSE statement regarding nitric oxide (NO):
A. NO acts as a vasodilator.
B. NO can be formed from one particular amino acid via the action of NO synthase.
C. NO activates adenylate cyclase and the resulting cAMP inhibits the action of certain protein kinases, causing muscle relaxation.
D. NO can inhibit platelet aggregation.
E. NO has a very short half-life in tissues and can lead to the generation of OH. radicals.
42. Select the one FALSE statement:
A. Type I muscle fibers contain myoglobin and mitochondria; their metabolism is predominantly aerobic.
B. Type II muscle fibers derive their energy predominantly from anaerobic glycolysis.
C. The amounts of type I and type II fibers can be altered by training.
D. In a marathon, blood glucose and free fatty acids are major energy sources.
E. In a 100 m sprint, anaerobic glycolysis is the sole energy source.
43. Select the one FALSE statement:
A. Microfilaments are composed of actin and myosin.
B. Microtubules contain α and β tubulins; the drugs colchicine and vinblastine bind to microtubules and inhibit their assembly.
C. Intermediate filaments include lamins and keratins.
D. Mutations affecting keratins are one cause of blistering.
E. Mutations in the gene encoding lamin A and lamin C cause progeria (accelerated aging).
44. Select the one FALSE statement:
A. Many but not all plasma proteins are synthesized by hepatocytes.
B. Haptoglobin is an acute phase glycoprotein that binds hemoglobin in the plasma and prevents it from entering the kidneys.
C. Many plasma proteins, such as haptoglobin, transferrin, and α1-antitrypsin, exhibit polymorphisms.
D. C-reactive protein (CRP) is a biomarker for many inflammatory states.
E. NFkB is an acute phase protein whose plasma level is elevated in acute inflammation.
45. Select the one FALSE statement:
A. Albumin is synthesized as a preproprotein.
B. Albumin is the major plasma protein by mass; it is not an acute phase protein.
C. Subjects with analbuminemia display severe edema.
D. Albumin binds many ligands, such as bilirubin, free fatty acids, copper, and certain drugs.
E. The plasma half-life of albumin can be markedly shortened in severe gastroenteropathies.
46. Select the one FALSE statement:
A. Transferrin shuttles ferric iron around the circulation.
B. Iron is absorbed in the duodenum in the ferrous state; a duodenal cytochrome b reduces ferric iron to the ferrous state.
C. Inside enterocytes, hephaestin oxidizes ferrous to ferric iron and the latter is then transferred to the plasma by the action of ferroportin.
D. Transferrin binds to transferrin receptor 1 (TfR1), is taken up by receptor-mediated endocytosis, and is then degraded inside endosomes.
E. Except in inflammation, levels of plasma ferritin are generally an indicator of body iron stores.
47. Select the one FALSE statement:
A. When intracellular levels of iron are high, ferritin is not synthesized but TfR1 is.
B. Hepcidin decreases iron absorption in the intestine by binding ferroportin and triggering its degradation.
C. The HFE protein can influence iron metabolism by up-regulating expression of hepcidin.
D. Levels of bone morphogenetic protein 6 can also affect regulation of hepcidin expression.
E. Ceruloplasmin, a copper-binding plasma protein, plays a role in iron metabolism by oxidizing ferrous iron to the ferric state.
48. You see a 50-year-old woman in clinic who is pale and tired. You suspect she has iron deficiency anemia. You order various lab tests, as shown below. Which result is NOT consistent with your provisional diagnosis ?
A. Low levels of plasma ferritin
B. Decreased saturation of transferrin
C. Decreased level of hemoglobin
D. Decreased level of red cell protoporphyrin
E. Increase of serum soluble TfR
49. You see a 57-year-old man in clinic who exhibits a green pigment ring around his cornea and also some signs of neurologic impairment. You suspect he has Wilson disease. Select the one FALSE statement regarding this condition:
A. Copper accumulates in the liver and brain.
B. It is caused by mutations in the copper-binding P-type ATPase that is involved in Menkes disease.
C. There is an increase of copper in Descemet’s membrane.
D. Levels of ceruloplasmin are generally low.
E. The condition responds to treatment with penicillamine, which chelates copper and removes it from the body in the urine.
50. Regarding amyloidosis, select the one FALSE statement:
A. It can be caused by a defect in amylase.
B. It can be caused by deposition of light chain fragments of immunoglobulins.
C. It can be caused by accumulation of degradation products of serum amyloid A.
D. It can be caused by accumulation of mutated plasma proteins such as transthyretin.
E. It can be caused by accumulation of β2-microglobulin.
51. Select the one FALSE statement:
A. Most but not all immunoglobulins are glycoproteins.
B. All immunoglobulins contain a minimum of two light and two heavy chains.
C. The type of heavy chain that an immunoglobulin contains determines its class.
D. The hypervariable regions of immunoglobulins comprise the antigen-binding sites and dictate the specificity of immunoglobulins.
E. The constant regions of immunoglobulins determine class-specific effector functions such as complement fixation and transplacental passage.
52. Select the one FALSE statement:
A. Junctional diversity reflects the addition or deletion of a random number of nucleotides when certain gene segments of antibodies are joined together.
B. In response to an immunogen, IgM molecules normally precede the appearance of IgG molecules in plasma; this is known as class switching.
C. Bence-Jones proteins are heavy chains of immunoglobulins that are overproduced in multiple myeloma.
D. Humanization of monoclonal antibodies involves attaching the complementarity-determining regions onto appropriate sites in a human immunoglobulin molecule, thus lessening immunogenicity.
E. The complement system consists of approximately 20 proteins and is involved in cell lysis, Inflammation, and clearance of antigen-antibody complexes from the circulation.
53. Which one of the following statements regarding the blood coagulation pathways is NOT CORRECT ?
A. The components of the extrinsic Xase (tenase) complex are factor VIIa, tissue factor, Ca2+, and factor X.
B. The components of the intrinsic Xase (tenase) complex are factor IXa, factor VIIIa, Ca2+, and factor X.
C. The components of the prothrombinase complex are factor Xa, factor Va, Ca2+, and factor II (prothrombin).
D. The extrinsic and intrinsic Xase complexes and prothrombinase complex require anionic procoagulant phosphatidylserine on LDL (low density lipoprotein) for their assembly.
E. Fibrin formed by cleavage of fibrinogen by thrombin is covalently cross-linked by the action of factor XIIIa, which itself is formed by the action of thrombin on factor XIII.
54. On which one of the following coagulation factors does a patient taking warfarin for his thrombotic disorder have decreased Gla (γ-carboxyglutamate) residues?
A. Tissue factor
B. Factor XI
C. Factor V
D. Factor II (prothrombin)
E. Fibrinogen
55. A 65-year-old male suffers a myocardial infarction and is given tissue plasminogen activator within 6 hours of onset of the thrombosis to achieve which one of the following?
A. Prevent activation of the extrinsic pathway of coagulation
B. Inhibit thrombin
C. Enhance degradation of factors VIIIa and Va
D. Enhance fibrinolysis
E. Inhibit platelet aggregation
56. Which one of the following statements regarding platelet activation in hemostasis and thrombosis is NOT CORRECT?
A. Platelets adhere directly to subendothelial collagen via GPIa-IIa and GPVI, while binding of GPIb-IX-V is mediated via von Willebrand factor.
B. The aggregating agent thromboxane A2 is formed from arachidonic acid liberated from platelet membrane phospholipids by the action of phospholipase A2.
C. The aggregating agent ADP is released from the dense granules of activated platelets.
D. The aggregating agent thrombin activates intracellular phospholipase Cβ, which forms the internal effector molecules 1,2-diacylglycerol and 1,4,5-inositol trisphosphate from the membrane phospholipid phosphatidylinositol 4,5-bisphosphate.
E. The ADP receptors, the thromboxane A2 receptor, the thrombin PAR-1 and PAR-4 receptors, and the fibrinogen GPIIb-IIIa receptor are all examples of G protein-coupled receptors.
57. A 15-year-old female presented at clinic with bruises on her lower extremities. Of the following, which is least likely to explain the bleeding signs exhibited by this individual?
A. Hemophilia A
B. von Willebrand disease
C. A low platelet count
D. Aspirin ingestion
E. A platelet disorder with absence of storage granules
58. Select the one FALSE statement:
A. Alpha-thalassemias are due to mutations affecting the alpha chains of hemoglobin.
B. Deficiency of either folic acid or vitamin B12 causes a megaloblastic anemia.
C. Hereditary spherocytosis is due to mutations affecting certain proteins of the red cell membrane.
D. Paroxysmal nocturnal hemoglobinuria (PNH) is due to mutations affecting synthesis of GPI-anchored proteins in the red cell membrane.
E. Mutations in the pyruvate kinase gene also cause PNH.
59. Select the one FALSE statement:
A. The red blood cell is highly dependent on glucose for its metabolism.
B. The red blood cell has a glucose transporter (GLUT1) that is estimated to contain 12 transmembrane helical segments.
C. The red blood cell has an active pentose phosphate shunt that generates NADPH.
D. The red blood cell has an active citric acid cycle.
E. The red cell contains certain enzymes involved in nucleotide metabolism, deficiencies of which can cause hemolytic anemia.
60. Regarding the anemia due to deficiency of G-6-P dehydrogenase, select the one FALSE statement:
A. It occurs extremely frequently in various parts of the world due to mutations in the gene encoding the enzyme.
B. It is a hemolytic anemia, and depending on severity, levels of conjugated bilirubin are often elevated as are levels of haptoglobin (Hp).
C. Mutant forms of the enzyme do not produce NADPH at normal levels.
D. Levels of reduced glutathione (GSH) are low in affected red cells because NADPH is needed to regenerate GSH from oxidized glutathione (GSSG).
E. Broad beans, because of their content of potential oxidants, may precipitate an attack, as may certain drugs such as primaquine (an anti-malarial).
61. All of the following proteins are present in the red cell membrane EXCEPT:
A. Pyruvate kinase
B. Spectrin
C. Ankyrin
D. Glycophorin
E. Anion exchange protein
62. Regarding the ABO blood group substances, select the one FALSE statement:
A. They can be either glycosphingolipids or glycoproteins, depending on location.
B. Individuals with blood group AB have antibodies to both A and B blood group substances.
C. Blood group H substance is formed from its precursor by the action of a fucosyltransferase.
D. Blood group B is formed from its precursor by the action of a galactosyltransferase.
E. Individuals of blood group O lack the galactosyltransferase.
63. Regarding various white blood cells, select the one FALSE statement:
A. Neutrophils possess integrins that are involved in their adhesion to endothelial cells.
B. A deficiency of a subunit common to several integrins affects the ability of neutrophils to bind to endothelial cells, and results in one type of leukocyte adhesion deficiency disease.
C. Lysozyme, which is abundant in macrophages, hydrolyzes the linkage between N-acetyl-neuraminic acid and N-acetyl-D-glucosamine found in certain bacterial cell walls, causing lysis.
D. Lactoferrin is a protein synthesized by neutrophils that binds iron, which may inhibit the growth of certain bacteria.
E. Myeloperoxidase can produce hypochlorous acid; this enzyme is responsible for the green color of pus.
64. Select the one FALSE statement:
A. NADPH oxidase is inactive in resting phagocytic cells.
B. The active form of NADPH oxidase contains cytochrome P450 and at least two other polypeptides.
C. The oxidase can be activated when phagocytic cells contact various ligands.
D. Activation of the oxidase leads to the production of superoxide from molecular oxygen, a phenomenon known as the respiratory burst.
E. Patients with mutations in any of the polypeptides present in the active enzyme do not generate sufficient superoxide to kill invading bacteria and fungi, and are susceptible to recurrent infections (chronic granulomatous disease).
65. Select the one FALSE statement:
A. Cytochrome P450 is a hemoprotein present in high concentration in the ER of liver that plays a key role in drug and xenobiotic metabolism.
B. The main reaction catalyzed by the enzyme is hydroxylation of a large number of different substrates.
C. It uses NADPH and requires NADPH-cytochrome P450 reductase for activity.
D. The reaction catalyzed by cytochrome P450 produces stoichiometric amounts of superoxide.
E. The enzyme is inducible by various drugs, a fact that may require changing the dose of other drugs that are being taken simultaneously.
66. Phase 2 reactions include all of the following EXCEPT:
A. Hydroxylation
B. Glucuronidation
C. Sulfation
D. Methylation
E. Acetylation
67. Select the one FALSE statement:
A. Glutathione (GSH) is a dipeptide derived from glutamic acid and cysteine.
B. Reduced GSH can be conjugated to a number of toxic electrophilic molecules, thus lessening their toxicity.
C. Metabolism of glutathione conjugates can lead to the production and subsequent urinary excretion of mercapturic acids.
D. GSH helps to maintain the SH groups of certain proteins in the reduced state.
E. GSH participates in the transport of certain amino acids across the plasma membrane of cells in a reaction catalyzed by γ-glutamyltransferase.
68. Which of the following is NOT a feature of the mitochondrial hypothesis of aging?
A. Reactive oxygen species are generated as a by-product by the electron transport chain.
B. Mitochondria lack the capacity to repair damaged DNA.
C. Many of the complexes in the electron transport chain are constructed from a mixture of subunits encoded by the nuclear genome and by the mitochondrial genome.
D. Damaged mitochondria form protease-resistant aggregates.
E. Damaged mitochondria can trigger apoptosis (programmed cell death).
69. Which of the following is NOT a component of the cell’s suite of damage repair and prevention agents?
A. Superoxide dismutase
B. Caspase 7
C. Glutathione
D. Isoaspartyl methyltransferase
E. Catalase
70. The cellular component that is most vulnerable, in terms of both susceptibility and potential consequences, is:
A. Phospholipids of membranes
B. Thymine dimers
C. Cysteine side-chains
D. The electron transport chain
E. DNA
71. Which of the following is an element of the metabolic theory of aging?
A. Large animals generally live longer because, statistically speaking, their larger chromosomes can adsorb more damage before suffering a mutation.
B. Calorically restricted diets tend to be life-extending because metabolic activity must decrease when the availability of nutrients is limited.
C. The heart is the most essential organ for life.
D. Damage by reactive oxygen species is multiplied by their tendency to participate in chain reactions.
E. Heartbeats are measured through the progressive shortening of telomeres.
72. Regarding chemical carcinogenesis, select the one FALSE statement:
A. Approximately 80% of human cancers may be due to environmental factors.
B. In general, chemical carcinogens interact non-covalently with DNA.
C. Some chemicals are converted to carcinogens by enzymes, usually cytochrome P450 species.
D. Most ultimate carcinogens are electrophiles and attack nucleophilic groups in DNA.
E. The Ames assay is a useful test for screening chemicals for mutagenicity; however, animal testing is required to show that a chemical is carcinogenic.
73. Regarding viral carcinogenesis, select the one FALSE statement:
A. Approximately 15% of human cancers may be caused by viruses.
B. Only RNA viruses are known to be carcinogens.
C. RNA viruses causing or associated with tumors include hepatitis C virus.
D. Retroviruses possess reverse transcriptase, which copies RNA to DNA.
E. Tumor viruses act by deregulating the cell cycle, inhibiting apoptosis and interfering with normal cell signaling processes.
74. Regarding oncogenes and tumor suppressor genes, select the one FALSE statement:
A. Both copies of a tumor suppressor gene must be mutated for its product to lose its activity.
B. Mutation of an oncogene occurs in somatic cells and is not inherited.
C. The product of an oncogene shows a gain of function that signals cell division.
D. RB and P53 are tumor suppressor genes; MYC and RAS are oncogenes.
E. Mutation of one tumor suppressor gene or one oncogene is thought to be sufficient to cause cancer.
75. Regarding growth factors, select the one FALSE statement:
A. They include a large number of polypeptides, most of which stimulate cell growth.
B. Growth factors can act in an endocrine, paracrine, or autocrine manner.
C. Certain growth factors, such as TGF-β, can act in a growth inhibitory manner.
D. Some receptors for growth factors have tyrosine kinase activity; mutations of these receptors occur in cancer cells.
E. PDGF stimulates phospholipase A2, which hydrolyzes PIP2to form DAG and IP3, both of which are second messengers.
76. Regarding the cell cycle, select the one FALSE statement:
A. The cell cycle has 4 phases (G1, S, G2and M).
B. Cancer cells usually have a shorter generation time than normal cells and there are less of them in Go phase.
C. A variety of mutations in cyclins and CDKs have been reported in cancer cells.
D. RB is a cell cycle regulator; it binds to transcription factor E2F, thus allowing progression of the cell from G1 to S phase.
E. When damage to DNA occurs, P53 increases in amount and activates transcription of genes that delay transit through the cycle.
77. Regarding chromosomes and genomic instability, select the one FALSE statement:
A. Cancer cells may have a mutator phenotype, which means that they have mutations in genes that affect DNA replication and repair, chromosomal segregation, DNA damage surveillance, and apoptosis.
B. Chromosomal instability refers to gain or loss of chromosomes caused by abnormalities of chromosomal segregation during mitosis.
C. Microsatellite instability involves expansion or contraction of microsatellites due to abnormalities of nucleotide excision repair.
D. Aneuploidy (when the chromosomal number of a cell is not a multiple of the haploid number) is a common feature of tumor cells.
E. Abnormalities of chromosome cohesion and of kinetochore-microtubule attachment may contribute to chromosomal instability and aneuploidy.
78. Select the one FALSE statement:
A. The activity of telomerase is frequently elevated in cancer cells.
B. A number of cancers have a hereditary predisposition, including Li-Fraumeni syndrome and retinoblastoma.
C. The products of BRCA1 and BRCA2 (responsible for hereditary breast cancer types I and II) appear to be involved in DNA repair.
D. Tumor cells usually exhibit a high rate of anaerobic glycolysis; this may be at least partly explained by the presence in many tumor cells of the PK-2 isozyme, which is associated with lesser production of ATP and possibly increased use of metabolites to build up biomass.
E. Dichloroacetate, a compound found to display some anti-cancer activity, inhibits pyruvate carboxylase, and thus diverts pyruvate away from glycolysis.
79. Select the one FALSE statement:
A. Whole-genome sequencing is revealing important new information about the numbers and types of mutations in cancer cells.
B. Abnormalities of epigenetic mechanisms, such as demethylation of cytosine residues, abnormal modification of histones, and aberrant chromatin remodeling are being increasingly detected in cancer cells.
C. Persistence of cancer stem cells (which are often relatively dormant and have active DNA repair systems) may help to explain some of the shortcomings of chemotherapy.
D. Angiogenin is a potent stimulator of angiogenesis.
E. Chronic inflammation, possibly via increased production of reactive oxygen species, predisposes to development of certain types of cancer.
80. Regarding apoptosis, select the one FALSE statement:
A. Apoptosis can be initiated by the interaction of certain ligands with specific receptors on cell surface.
B. Cell stress and other factors activate the mitochondrial pathway of apoptosis; release of cytochrome P450 into the cytoplasm is an important event in this pathway.
C. A distinct pattern of fragments of DNA is found in apoptotic cells; it is caused by caspase-activated DNase.
D. Caspase 3 digests cell proteins such as lamin, certain cytoskeletal proteins, and various enzymes, leading to cell death.
E. Cancer cells have acquired various mutations that allow them to evade apoptosis, prolonging their existence.
81. Select the one FALSE statement:
A. Proteins involved in cell adhesion include cadherins, integrins, and selectins.
B. Decreased amounts of E-cadherin on the surfaces of cancer cells may help account for the decreased adhesiveness shown by tumor cells.
C. Increased activity of GlcNAc transferase V in cancer cells may lead to an altered glycan lattice at the cell surface, perhaps predisposing to their spread.
D. Cancer cells secrete metalloproteinases that degrade proteins in the ECM and facilitate their spread.
E. All tumor cells have the genetic capacity to colonize.
82. Of the following, the best test of renal function is:
A. Measurement of blood urea
B. Measurement of urinary protein
C. Creatinine clearance
D. Measurement of urinary ammonia
E. Measurement of urinary volume
83. A test that assesses the synthetic function of liver is:
A. Serum albumin levels
B. Serum conjugated (direct) bilirubin levels
C. Serum alanine transaminase (ALT)
D. Serum alkaline phosphatase (ALP)
E. Blood ammonia
84. All of the following are characteristics of a substance whose clearance is indicative of the glomerular filtration rate (GFR) EXCEPT:
A. It should have stable blood levels.
B. It should be freely filtered at the glomerulus.
C. It should be completely reabsorbed by the renal tubule.
D. It should not be secreted by the renal tubule.
E. It should not be metabolized in the body.
85. The first test that should be done in the assessment of thyroid function is the measurement of:
A. Total thyroxine
B. Thyroid stimulating hormone (TSH)
C. Free thyroxine and triiodothyronine
D. Thyrotropin releasing hormone (TRH)
E. Thyroid binding globulin (TBG)
86. In relation to adenosine deaminase (ADA) deficiency, select the one FALSE statement:
A. Deficiency of ADA accounts for the majority of cases of severe combined immunodeficiency disease (SCID).
B. Increased levels of dATP resulting from deficiency of ADA are toxic to T lymphocytes.
C. Conjugation of ADA to polyethylene glycol (PEG) prolongs the life in the circulation of the enzyme.
D. Integration of a gene via gene therapy can, in some cases, cause cancer by insertional mutagenesis.
E. Criteria to be satisfied prior to administration of gene therapy include that the gene administered should show sufficient levels of expression, it should be regulated, and there should be no significant side effects.
87. In relation to Alzheimer disease (AD), select the one FALSE statement:
A. Only about 10% of cases of AD appear to have a genetic basis.
B. Deposition of amyloid β-peptide (Aβ42) followed by its aggregation secondary to oligomerization and formation of β-sheets is thought by some to play a central role in the causation of AD.
C. Aβ42 is derived from amyloid precursor protein (APP), a transmembrane protein; APP is a substrate for several proteases (secretases).
D. Genes involved in AD include APOE4, which appears to increase deposition of Aβ42.
E. Another important feature of AD is deposition of a phosphorylated form of tau, a microtubule-associated protein, which forms neuritic tangles.
88. In relation to cholera, select the one FALSE statement:
A. Cholera is due to infection by the bacterium V cholera, which secretes an enterotoxin.
B. Cholera toxin has A and B subunits; the B subunits interact with the ganglioside GM1 present on the plasma membrane of intestinal cells.
C. The A subunit uses NAD to ribosylate the Gs subunit of adenylate cyclase, up-regulating it and increasing formation of cAMP, which in turn activates protein kinase A (PKA).
D. PKA phosphorylates various target proteins, resulting in massive loss of NaCl into the gut.
E. Therapy for treatment of cholera includes immediate replacement of lost fluid and administration of an appropriate antibiotic; thereafter, taking oral rehydration solution (containing glucose, sodium chloride, sodium citrate, and sodium bicarbonate) has proven very effective.
89. Regarding colorectal cancer, select the one FALSE statement:
A. Colorectal cancers can arise from adenomatous polyps.
B. Specific oncogenes and tumor suppressor genes have been shown to be involved in its causation.
C. Environmental factors - such as a diet high in saturated fat and low in fiber - have also been proposed to be involved in its causation.
D. CEA is a glycoprotein that is released into the plasma from the surface membranes of certain cells.
E. CEA is an excellent test, with high sensitivity and high specificity, for detecting the presence of colorectal cancer.
90. Regarding cystic fibrosis (CF), select the one FALSE statement:
A. CF is a genetic disease due to mutations in the CFTR gene.
B. The CFTR gene was discovered because of its association with a characteristic massive deletion located on chromosome 7.
C. Over 1,000 different mutations have been reported in the gene since its discovery.
D. The CF gene encodes a cAMP-responsive chloride transporter; abnormalities of the transporter lead to decreased secretion of chloride from epithelial cells and high chloride content in sweat.
E. Viscous mucus can obstruct pancreatic ducts, leading to a deficiency of various digestive enzymes in the gut causing malnutrition, and its presence in the respiratory tract favors the growth of nasty bacteria such as Pseudomonas aeruginosa.
91. Regarding diabetic ketoacidosis (DKA), select the one FALSE statement:
A. Over-production of ketone bodies in DKA is caused by breakdown of fats due to lack of insulin; it results in acidosis.
B. The ketone bodies are β-hydroxybutyric acid and acetoacetic acid.
C. The anion gap (plasma Na+- [Cl– + HCO3–]) is elevated in DKA, but also in other conditions such as lactic acidosis and intoxication by salicylates.
D. Plasma levels of K+ are often elevated in DKA because of lack of insulin.
E. Appropriate initial treatment of DKA is administration of insulin and i.v. saline; glucose and KCl are added later.
92. Regarding Duchenne muscular dystrophy (DMD), select the one FALSE statement:
A. Creatine kinase MB is an important enzyme to measure in the diagnosis of DMD.
B. DMD is an X-linked degenerative disease of muscle.
C. The protein affected in both DMD and Becker muscular dystrophy is dystrophin.
D. Dystrophin is a very large protein associated with the sarcolemma of muscle.
E. Mutations affecting muscle proteins encoded by various genes have been shown to be the causes of a variety of other types of muscular dystrophy.
93. Regarding ethanol intoxication, select the one FALSE statement:
A. Increased production of NADH, via the alcohol dehydrogenase (ADH) reaction, favors the formation of lactate from pyruvate.
B. The resulting diminution of the level of pyruvate required for the pyruvate carboxylase reaction inhibits gluconeogenesis and may promote hypoglycemia.
C. Acetaldehyde, produced by the ADH reaction, is a highly reactive molecule, and may be responsible for some of the toxic effects of ethanol.
D. Ethanol may interpolate into membranes and also interacts with ion channels, affecting their functions.
E. Ethanol is metabolized exclusively by alcohol dehydrogenase.
94. Regarding gout, select the one FALSE statement:
A. Gout is due to accumulation of uric acid in one or more joints and other tissues, causing acute or chronic inflammation.
B. Uric acid is the end-product of purine and pyrimidine metabolism.
C. Uric acid is produced from xanthine via the action of xanthine oxidase; humans lack the enzyme uricase, so we cannot produce allantoin.
D. Decreased excretion of uric acid is the major cause of gout.
E. Acute attacks of gout are treated using anti-inflammatory drugs or colchicine; allopurinol, which inhibits xanthine oxidase, is a useful drug for the longer-term treatment of gout.
95. Regarding hereditary hemochromatosis, select the one FALSE statement:
A. The hallmark of hereditary hemochromatosis is an increase of total body iron, sufficient to cause tissue damage.
B. Free iron is toxic because it can generate free radicals via the Fenton reaction.
C. Elevated levels of transferrin saturation and of serum ferritin are the most useful tests for early diagnosis.
D. The most common cause of the condition is mutations in the gene encoding the protein HFE; the primary role of HFE is regulation of the level of hepcidin.
E. Chelation therapy to remove excess iron is the preferred treatment for this condition.
96. Regarding hypothyroidism, select the one FALSE statement:
A. Causes of primary hypothyroidism include deficient intake of iodine and Hashimoto disease (an autoimmune condition).
B. Symptoms include chronic fatigue, sluggishness, constipation, and cold intolerance.
C. Congenital hypothyroidism can and should be detected by routine screening of levels of TSH at birth.
D. Elevated levels of TSH and of T4 are highly indicative of hypothyroidism.
E. Treatment of primary hypothyroidism consists of judicious administration of thyroxine (T4), generally for life.
97. Regarding protein-energy malnutrition (PEM), select the one FALSE statement:
A. Oxidative stress, by affecting vascular permeability, may contribute to the clinical picture of kwashiorkor.
B. Signs of kwashiorkor include thin hair, apathy, fatty liver, protuberant abdomen, fragile skin, and diminished body fat.
C. Edema is usually a feature of kwashiorkor; contributing factors to its development may be hypoalbuminemia and deficient dietary intake of methionine.
D. Low levels of insulin and cortisol contribute to the muscle wasting seen in marasmus.
E. PEM is entirely preventable by a well-balanced diet.
98. Regarding myocardial infarction (MI), select the one FALSE statement:
A. The major cause of an MI is an occlusive thrombus occurring in close proximity to an atherosclerotic plaque which may have ruptured recently.
B. Serial measurements of CK-MB is the best lab test in helping to confirm the diagnosis of MI.
C. The presence of oxidized LDL in a plaque encourages recruitment of inflammatory cells, which are thought to be important contributors to atherosclerosis.
D. Contributors to cell death in an MI include depletion of ATP, activation of various degradative enzymes, and accumulation of intracellular Ca2+.
E. One treatment for MI is administration of t-PA; this enzyme can help dissolve the thrombus and prevent further cardiac damage when given as soon as possible.
99. Regarding obesity, select the one FALSE statement:
A. A body mass index (BMI) of over 30 is indicative of obesity.
B. Obesity predisposes to various conditions including the metabolic syndrome; this includes excess abdominal fat, high blood glucose, increased LDL and decreased HDL, and high blood pressure.
C. Neuropeptide Y and melanocyte stimulating hormone (α-MSH) increase appetite.
D. Elevated levels of leptin, a polypeptide released by adipocytes, decrease food intake and also increase energy expenditure.
E. Brown adipose tissue contains a mitochondrial protein, thermogenin, that dissipates energy as heat; differences in amounts of this protein and perhaps of other uncoupling proteins may play a role in the causation of obesity.
100. Regarding osteoporosis, select the one FALSE statement:
A. Osteoporosis is a reduction of bone mass or density.
B. In osteoporosis, a normal ratio of bone mineral (hydroxyapatite) to bone matrix (mostly collagen type I) is preserved.
C. In osteomalacia, as caused by deficiency of vitamin C, decreased mineralization is present.
D. Decline in levels of estrogen appears to increase the secretion of a number of cytokines that lead to the recruitment of osteoclasts, stimulating increased resorption.
E. Levels of serum Ca, P, alkaline phosphatase, 25-hydroxyvitamin D, and parathyroid hormone may all be normal in osteoporosis.
101. Regarding xeroderma pigmentosum (XP), select the one FALSE statement:
A. This condition is due to mutations in any one of at least 7 genes involved in the mismatch DNA repair pathway.
B. UV irradiation can cause the formation of thymine dimers, in which covalent bonds are formed between adjacent intrachain thymine residues.
C. The formation of thymine dimers can be measured in fibroblasts taken from a patient.
D. Patients with XP develop cancers at an early age because of the defect in DNA repair; UV irradiation may activate oncogenes or inactivate tumor suppressor genes.
E. Patients with XP should be followed up closely and advised to avoid exposure to sunlight and to use appropriate sunscreen ointments.
REFERENCES
MacDonald RG, Chaney WG: USMLE Road Map:Biochemistry. McGraw-Hill Lange, 2007.
Toy EC, Seifert WE, Strobel HW, Harms KP: Case Files Biochemistry. McGraw-Hill Lange, 2008.