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[MCQs] Protein Function and Bioenergetics Quiz (35 test)

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Protein Function and Bioenergetics Quiz (35 test)

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1. A 72-year-old African American female with emphysema presents to the emergency room with fatigue and respiratory distress. Which of the following sets of arterial blood gas values would represent her condition and reflect a shift of the hemoglobin oxygen-dissociation curve to the right?

  1. pH 05, bicarbonate 35 mEq/L, PCO2 60, Po2 8
  2. pH 35, bicarbonate 10 mEq/L, PCO2 30, Po2 98
  3. pH 35, bicarbonate 15 mEq/L, PCO2 30, Po2 98
  4. pH 4, bicarbonate 24 mEq/L, PCO2 60, Po2 88
  5. pH 45, bicarbonate 15 mEq/L, PCO2 60, Po2 88

2. The small town doctor in the movie Doc Hollywood impresses the aspiring plastic surgeon by treating a cyanotic child with a soft drink, knowing the child has reduced hemoglobin from drinking well water. The ability of hemoglobin to serve as an effective transporter of oxygen and carbon dioxide between lungs and tissues is explained by which of the following properties?

  1. The isolated heme group with ferrous iron binds oxygen much more avidly than carbon
  2. The α- and β-globin chains of hemoglobin have very different primary structures than
  3. Hemoglobin utilizes oxidized ferric iron to bind oxygen, in contrast to the ferrous ion of
  4. In contrast to myoglobin, hemoglobin exhibits greater changes in secondary and tertiary structures after oxygen
  5. Hemoglobin binds proportionately more oxygen at low oxygen tension than does

3. A previously healthy 2-year-old Caucasian boy becomes gray and dusky-looking and is brought to his physician with suspicion of heart disease. Rather than doing a cardiac evaluation, the physician asks about the family’s water supply and notes that they are farmers using well water. The physician then provides some oxygen and vitamin C with rapid improvement of the child’s The child’s problem was most likely due to which of the following?

  1. Nitrates in well water cause reduced hemoglobin (methemoglobin) and cyanosis in all families
  2. Cyanide in well water poisoning the respiratory chain
  3. Nitrates in well water interacting with heterozygous methemoglobin reductase deficiency to produce methemoglobin
  4. Nitrates in well water competing for hemoglobin oxygen binding, producing a sigmoidal binding curve
  5. Carbon dioxide released by methane fuels causing decreased hemoglobin O2affinity

4. Sickle cell anemia (MIM*604903) was one of the first disorders selected for newborn screening despite concerns about stigmatization from the African American The disease results from homozygous mutation causing substitution of valine for glutamate at position 6 on the β chain of hemoglobin, producing hemoglobin S. Which of the following techniques might be considered for hemoglobin S screening?

  1. Decreased polymerization of deoxyhemoglobin
  2. Altered electrophoretic mobility
  3. Increased solubility of deoxyhemoglobin
  4. More flexible red blood cells
  5. Unchanged primary structure

5. An increased affinity of hemoglobin for O2 may result from which of the following?

  1. Acidosis
  2. Lower 2,3-bisphosphoglycerate (BPG) levels within erythrocytes
  3. High CO2 levels
  4. More ferric ion
  5. Initial binding of O2 to one of the four sites available in each deoxyhemoglobin molecule

6. A middle-aged man is brought to the emergency room in coma, well known to the medical staff because of alcoholism and progressive liver His current measure of serum glutamine-oxalate aminotransferase (AST), an enzyme used as a marker of liver cell damage, is reported as 1500 μmol/min per mg protein, elevated but not as high as previous values in the 20,000 range. The lower AST activity contrasts with other measures of liver disease, including a serum ammonia in the 750 range (normal less than 30) and decreased amounts of coagulation factor proteins (these changes, respectively, account for the coma and bleeding tendencies of advanced liver disease). A call to the laboratory reveals that an inexperienced technologist is on duty, who emphasizes that he has performed the assay in the standard way. Which of the following is the most likely reason for the lower AST activity?

  1. Measure of activity rather than specific activity
  2. Inappropriate units for measure of specific activity
  3. Substrate concentration similar to the value of Km
  4. Lack of dilution with too much enzyme for substrate
  5. Lack of dilution with too much substrate for enzyme

7. A 65-year-old Hispanic female delays evaluation of a breast lump and presents to her physician with a fungating surface She also has severe diabetes and heart disease that prevent radical surgery, so her physician decides upon local surgery with surface chemotherapy that includes the drug fluorouracil. This agent blocks the activity of thymidylate synthase by which of the following mechanisms?

  1. Allosteric inhibition
  2. Competitive inhibition
  3. Irreversible inhibition
  4. Noncovalent inhibition
  5. Noncatalytic inhibition

8. A 28-year-old African American female develops extreme fatigue with vomiting and anorexia after eating oysters and her husband notes a yellow hue to the whites of her eyes. Her physician recognizes her jaundiced sclerae and does laboratory testing that shows a serum aspartate aminotransaminase (AST or SGOT) level of 3000 U/L (normal 15-45) along with other abnormalities that suggest liver Antigen studies confirm a diagnosis of hepatitis A and the physician follows his patient with AST levels of 3050 U/L at day 2, 3075 at day 4, and 2950 at day 6. The physician is puzzled because the similar AST levels seem to show no progression of hepatitis, yet his patient has developed severe liver disease with coma due to high ammonia levels and copious bleeding from coagulopathy. Which of the following is the most likely explanation?

  1. Constant liver cell death with selective effects on coagulation proteins
  2. Assay of ALT enzyme with inadequate substrate levels
  3. Assay of ALT enzyme with inadequate product levels
  4. Inappropriate assay of ALT enzyme from dilute serum
  5. Inappropriate assay of ALT enzyme from undialyzed serum

9. In the study of enzymes, a sigmoidal plot of substrate concentration ([S]) versus initial reaction velocity (Vi) may indicate which of the following?

  1. Michaelis–Menten kinetics
  2. Competitive inhibition
  3. Noncompetitive inhibition
  4. Cooperative binding
  5. Suicidal inhibition where the enzyme catalyzes the formation of inhibitor

10. A noncompetitive inhibitor of an enzyme does which of the following?

  1. Decreases Vmax
  2. Increases Vmax
  3. Decreases Km and decreases Vmax
  4. Increases Km and increases Vmax
  5. Increases Km with no or little change in V max

11. In the 1980s, biochemically oriented researchers focused on the enzyme superoxide dismutase (SOD) as a potential cause of Down The trisomy (three doses) of chromosome 21 in that disorder would produce three copies of the SOD gene that is located on chromosome 21. SOD acts to remove superoxide anion free radical, catalyzing the reaction of two superoxide radicals with two hydrogen ions to form hydrogen peroxide and oxygen. Reasoning that the increased SOD activity and its excess peroxide products might cause embryonic birth defects, researchers constructed a mouse with three doses of the gene encoding SOD. Instead of simulating the multiple developmental changes of Down syndrome, mice with triplicated SOD loci had no abnormalities at all. Which of the following is the most likely fallacy in this research approach?

  1. SOD enzyme assays with inadequate substrate
  2. Lack of attention to the concept of enzyme reserve, where most enzymes are present in excess of in vivo substrate
  3. Lack of attention to colinked peroxidase loci that will also be increased in Down
  4. Effects of human genetic mutations cannot be replicated in
  5. Lack of attention to potential repressive mechanisms that negate extra doses of enzyme-encoding

12. Which of the following enzymes is regulated primarily through allosteric interaction?

  1. Aspartate transcarbamoylase
  2. Chymotrypsin
  3. Glycogen phosphorylase
  4. Glycogen synthase
  5. Pyruvate dehydrogenase

13. Which of the following enzymes exhibits a hyperbolic curve when initial reaction velocity is plotted against substrate concentration?

  1. Aspartate transcarbamoylase
  2. Phosphofructokinase
  3. Hexokinase
  4. Pyruvate kinase
  5. Lactate dehydrogenase

14. Which of the following is an accurate description for the process of rigor mortis?

  1. Intracellular levels of ATP drop, so ATP is not available to bind the S1 head of myosin; thus, actin does not dissociate from
  2. Intracellular levels of ATP drop, so ATP is not available to bind the S1 head of myosin; thus, actin dissociates from
  3. Intracellular levels of ATP rise, so ATP is available to bind the S1 head of myosin; thus, actin dissociates from
  4. Intracellular levels of ATP rise, so ATP is available to bind the S1 head of myosin; thus, actin does not dissociate from
  5. Intracellular levels of ATP rise, producing more ADP that counteracts

15. A group of congenital disorders exhibit multiple joint contractures at birth, described by the term “arthrogryposis” (arthro = joint, gryposis = contracture). A subgroup involves decreased fetal muscle function with resulting deformation (contracture) of the limbs by surrounding uterine forces to produce deviated hands, clubfeet, etc. Mutations in which of the following proteins or protein fragments would be most likely in an otherwise normal neonate with arthrogryposis due to skeletal muscle dysfunction?

  1. Light meromyosin component of myosin II
  2. S-2 fragment of myosin-II
  3. Troponin complex proteins
  4. Tropomyosin
  5. Myosin-I

16. A 2-week-old Caucasian boy returns to his pediatrician for neonatal follow-up after a newborn screen revealed elevation of citric acid cycle intermediates including succinate and fumarate. He has been feeding poorly, and his weight gain is less than the ½ oz per day expected after accounting for the expected 5% to 10% loss from birth Repeat screen again shows elevations of citrate, α-ketoglutarate, and succinate plus a venous lactate of 6.5 mmol/L (normal 0.5-2.2). The infant is referred to a metabolic clinic where skin biopsy and fibroblast studies reveal deficient yield of carbon dioxide, GTP, and NAD+. Which of the steps shown in the following diagram of the citric acid cycle could account for all three deficiencies?

  1. Step A
  2. Step B
  3. Step C
  4. Step D
  5. Step E

17. A comatose 25-year-old Asian female is brought by ambulance to the emergency room from a campus chemistry laboratory where she works as a teaching assistant. Vital signs reveal a temperature of 40.5°C (105°F) with rapid heart and respiratory rates. Along one arm is a yellow stain and her blood pressure is Two students accompany her and report that she was giving a demonstration on metabolic inhibitors and had an accidental spill on her face, first joking and complaining of blurred vision, then having headaches and shaking movements before passing out. Which of the following is the most likely toxin?

  1. Phenobarbital
  2. Carboxin
  3. Dimercaprol
  4. Dinitrophenol
  5. Cyanide

18. Dehydrogenases such as glucose-6-phosphate dehydrogenase serve to transfer H+ from one substrate to another in coupled oxidation-reduction reactions, ultimately (in the respiratory chain) generating energy by oxygen/water reduction. Dehydrogenases can use which of the following compounds as an electron acceptor?

  1. H2O
  2. NAD+
  3. O2
  4. Peroxide
  5. NADPH

19. Nicotine addiction from cigarette smoking is related to rates of conversion of nicotine to cotinine, carried out by a member of the cytochrome P450 enzyme family called P450PB (formerly CYP2A3-MIM*122720). Individuals with variant alleles of the enzyme are predisposed toward nicotine addiction and the development of lung The P450 cytochromes are members of which family of oxidoreductases?

  1. Catalase
  2. Hydroperoxidase
  3. Oxidase
  4. Oxygenase
  5. Dehydrogenase

20. Which of the following compounds is a high-energy phosphate donor to ATP during glycolysis?

  1. Glucose 6-phosphate
  2. Glucose 1-phosphate
  3. Phosphoenolpyruvate
  4. Phosphoglyceric acid
  5. Fructose 6-phosphate

21. Which of the following are products of triacylglycerol breakdown and subsequent β-oxidation that may undergo gluconeogenesis?

  1. Propionyl-CoA
  2. Acetyl-CoA
  3. All ketone bodies
  4. Some amino acids
  5. β-Hydroxybutyrate

22. Which of the following regulates lipolysis in adipocytes?

  1. Activation of fatty acid synthesis mediated by cyclic AMP
  2. Activation of triglyceride lipase as a result of hormone-stimulated increases in cyclic AMP levels
  3. Glycerol phosphorylation to prevent futile esterification of fatty acids
  4. Activation of cyclic AMP production by insulin
  5. Hormone-sensitive lipoprotein lipase

23. Oligomycin is an antibiotic derived from Streptomyces, a genus of soil bacteria that has contributed over two-thirds of naturally derived antibiotics used in Oligomycin is a macrolide antibiotic (containing a large macrolide ring-like erythromycin or azithromycin) that inhibits ATP synthase required for oxidative phosphorylation. Which of the following options best explains the consequence of this inhibition?

  1. Selective disruption of complex II function
  2. Disruption of ubiquinone phosphorylation
  3. Disruption of NADH entry into the respiratory chain
  4. Disruption of proton flow across the inner mitochondrial membrane
  5. Disruption of heme oxygen action

24. Patients with fatty acid oxidation disorders are particularly susceptible to periods of fasting with disproportionate impact on muscular This is because, relative to energy from oxidation of glycogen (4 kcal/g or, when hydrated, 1.5 kcal/g), the yield from oxidation of triacylglyceride stores is which of the following?

  1. 1 kcal/g
  2. 2 kcal/g
  3. 4 kcal/g
  4. 9 kcal/g
  5. 24 kcal/g

25. A 24-hour-old Caucasian female infant has a rapid respiratory rate, often due to retained fluid from delivery (transient tachypnea of the newborn). The child then has feeding problems due to low muscle tone (hypotonia), and this seems to have central (nervous system) rather than peripheral origin, implying an A liver biopsy reveals a very low level of acetyl-CoA carboxylase, but normal levels of the enzymes of glycolysis, gluconeogenesis, the citric acid cycle, and the pentose phosphate pathway. Which of the following is the most likely cause of the infant’s respiratory problems?

  1. Low levels of phosphatidylcholine
  2. Excess adrenal fatty acids
  3. Ketoacidosis
  4. High levels of citrate
  5. Glycogen depletion

26. Patients with riboflavin deficiency will have lower FAD levels, while those with niacin deficiency will have lower NAD How do oxidations involving NAD compare with those involving FAD?

  1. NAD-linked oxidations generate 3 mol ATP per half mole of O2 consumed, whereas FAD-linked oxidations only generate 2 mol ATP per half mole of O2consumed.
  2. FAD-linked oxidations generate 3 mol ATP per half mole of O2 consumed, whereas NAD-linked oxidations only generate 2 mol ATP per half mole of O2
  3. Both oxidations generate 2 mol ATP per half mole of O2
  4. Both oxidations generate 3 mol ATP per half mole of O2
  5. Both oxidations add hydrogens to

27. Individuals with disorders of the respiratory chain are often placed on supplements containing riboflavin and coenzyme Which of the following is the role of coenzyme Q (ubiquinone) in the respiratory chain?

  1. It links flavoproteins to cytochrome b, the cytochrome of lowest redox
  2. It links NAD-dependent dehydrogenases to cytochrome
  3. It links each of the cytochromes in the respiratory chain to one
  4. It is the first step in the respiratory
  5. It is a hydrogen receptor from

28. In the resting state, what is the primary condition that limits the rate of respiration?

  1. Availability of ADP
  2. Availability of oxygen
  3. Availability of substrate
  4. Availability of both ADP and substrate
  5. Availability of oxygen and ATP

29. Oxidative phosphorylation couples generation of ATP with which of the following?

  1. Proton translocation
  2. Substrate level phosphorylation
  3. Electron flow through cytochromes
  4. Reduction of NADH
  5. Reduction of water

30. In the past, the uncoupler 2,4-dinitrophenol was used as a weightreducing drug until side effects such as fatigue and breathlessness precluded its How could the use of this drug result in weight loss?

  1. 2,4-dinitrophenol is an allosteric activator of ATP synthase and thus increases the rate of H+ translocation and oxidation of fats and other
  2. 2,4-dinitrophenol inhibits transport of pyruvate into the Fats are therefore metabolized to glycerol and subsequently to pyruvate, depleting fat stores.
  3. 2,4-dinitrophenol allows oxidation of fats in adipose tissue without production of Fat oxidation can thus proceed continuously and fat stores will be used  up.
  4. 2,4-dinitrophenol causes ATP to be produced at a higher rate than normal, thus causing weight
  5. 2,4-dinitrophenol causes ADP to decrease and thus to increase rates of oxidative

31. Many compounds poison the respiratory chain by inhibiting various steps of oxidation or Which of the following steps is inhibited by carbon monoxide and cyanide?

  1. Oxidation step between cytochrome and coenzyme Q and distal cytochromes
  2. Oxidation step involving direct reduction of oxygen
  3. Uncoupling of oxidation from phosphorylation
  4. Oxidation step between cytochromes c and b
  5. Oxidation step of flavin cytochromes to coenzyme Q

32. An important difference between respiratory chain inhibitors and uncouplers is which of the following?

  1. The effect of respiratory chain inhibitors cannot be characterized spectroscopically, whereas that of uncouplers
  2. Uncouplers do not inhibit electron transport, but respiratory chain inhibitors
  3. Uncouplers are toxic substances, but respiratory chain inhibitors are
  4. Respiratory chain inhibitors allow leakage of protons across the membrane, but uncouplers do
  5. Uncouplers accept protons from NADH before they can be transported across the mitochondrial

33. Why is the yield of ATP from the complete oxidation of glucose lower in muscle and brain than in kidney, liver, and heart?

  1. Different shuttle mechanisms operate to transfer electrons from the cytosol to the mitochondria in the two sets of
  2. Muscle and brain cells have a lower requirement for
  3. There are fewer mitochondria in muscle and brain
  4. There are fewer ATP synthases in muscle and brain
  5. Mitochondrial glycerophosphate dehydrogenase uses NAD rather than

34. The problem of regenerating NAD+ from NADH for cytoplasmic processes by using mitochondria is solved in the most energy-efficient manner by which of the following?

  1. Reversing the direction of enzyme reactions like pyruvate dehydrogenase
  2. Locating certain cytochromes in the cytoplasm
  3. Shuttling of coupled reaction substrates like malate to aspartate
  4. Reversing the direction of glycolysis
  5. Direct oxidation of NADH by cytochromes P450

35. A certain class of disease is produced because of the tissue’s lack of certain metabolic Which one of the following tissues can metabolize glucose, fatty acids, and ketone bodies for ATP production?

  1. Liver
  2. Muscle
  3. Hepatocytes
  4. Brain
  5. Red blood cells

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