PART I. (60 points)
Type A. Each of the following statements is followed by five suggested answers or completions. On the answer sheet, mark the one which is best in each case.
1. Sensitivity to the antimalarial drug, primaquine, occurs in men with mutations in
A. hexokinase.
B. glucose 6-phosphatase.
C. phosphoglucomutase.
D. glucose 6-phosphate dehydrogenase.
E. pyruvate kinase.
2. A significant biochemical role of vitamin C has been described in
A. bone formation.
B. prevention of the common cold.
C. oxidation of carotenes to vitamin D.
D. metabolic functions of zinc.
E. steroid hydroxylation.
3. A patient has thrown a blood clot to the lung following surgery. To prevent further embolus formation, you would most like inject
A. EDTA to bind serum calcium.
B. heparin I.V.
C. warfarin I.V.
D. protamine I.V.
4. The specific Ca2+ binding protein of the myofibril is
A. G actin
B. tropomyosin
C. troponin C
D. alpha actinin
E. none of the above
5. Which of the following reactions involving Vitamin A occurs as a result of absorption of a photon of light?
A. hydrolysis of a retinal-phosphatidylethanolamine complex.
B. 11-cis retinal to trans retinal.
C. trans retinol to 11-cis retinal.
D. retinol to retinal.
E. beta-carotene to retinal.
6. The protein which becomes an instantly acting protease inhibitor in the presence of heparin is
A. alpha1 antitrypsin
B. alpha2 macroglobulin
C. tissue factor
D. high molecular weight kininogen
E. antithrombin III
7. Each of the following enzymes requires pyridoxal phosphate as a coenzyme EXCEPT which one?
A. ALA-synthetase
B. lactic dehydrogenase
C. glutamic decarboxylase
D. histidine decarboxylase
E. aspartate aminotransferase
8. The immediate precursor of heme in its synthesis is
A. protoporphyrin IX.
B. coproporphyrinogen III.
C. uroporphyrinogen III.
D. porphobilinogen.
E. bilirubin.
9. The bile pigments result from degradation of
A. globin.
B. gallstones.
C. cholesterol.
D. heme.
E. uric acid.
10. Cholera toxin exerts its effects on cells of the intestinal mucosa by
A. activation of the GTP-binding protein by ADP-ribosylation.
B. ADP-ribosylation of factor EF-2.
C. inactivation of the GTP-binding protein by ADP-ribosylation.
D. binding to a transcription factor.
E. activation of guanylate cyclase.
11. Iron is transported in the plasma primarily as
A. transferrin complex with Fe+2.
B. transferrin complex with Fe+3.
C. ferritin complex.
D. free ferrous ion.
E. heme containing enzymes.
12. Structure of collagen includes all of the following structural features EXCEPT
A. left-handed helix.
B. triple helix.
C. over 1/4 of the amino acids are Gly.
D. extracellular removal of N-terminus.
E. cross link between adjacent histidines.
13. The following are TRUE statements concerning catecholamines EXCEPT
A. dopamine cannot pass the blood brain barrier and is provided to patients with Parkinson's disease in the form of DOPA.
B. the synthesis of epinephrine requires tetrahydrobiopterin and SAM as cofactors.
C. synthesis of epinephrine and norepinephrine takes place in the adrenal medulla.
D. NAD+ is required in the conversion of DOPA to dopamine.
E. catabolism of catecholamines involves oxidative removal of the amino groups by monoaminooxidase (MAO) and methylation of OH-groups by catechol-O-methyltransferase (COMT).
14. Receptor-mediated endocytosis (RME) is a mechanism whereby iron is taken up by the cell. True statement(s) regarding RME include all of the following EXCEPT:
A. the internalized receptors are recycled.
B. the receptors become localized in specialized regions called coated pits.
C. a proton pump is important for release of the iron.
D. the receptor is fixed in the coated pit-vesicle by interaction with the protein clathrin.
E. the receptor remains in the membrane while the iron is internalized.
15. Which of the following does NOT occur when a RBC returns to the Lungs from the peripheral tissues?
A. Deoxyhemoglobin is oxygenated.
B. Chloride migrates from the erythrocyte to the plasma.
C. Bicarbonate migrates from the plasma into the erythrocyte.
D. Hydrogen ions are released from hemoglobin.
E. 2,3 bis phosphoglycerate binding to hemoglobin is increased.
16. The repeating unit of hyaluronic acid is composed of combinations of which of the following kinds of carbohydrates?
A. a uronic acid and an amino sugar
B. Galactose and glucose
C. Fructose and glucose
D. Sialic acid and an amino sugar
E. Mannose and an amino sugar
17. In skeletal muscle fibers the thin filament consists of a double stranded chain of "beads". These thin filaments are
A. myosin
B. troponin
C. fibrin
D. actin
E. lectin
18. This amino acid and a 4 carbon intermediate from the tricarboxylic acid cycle condense in the first step of the biosynthesis of heme:
A. valine
B. aspartate
C. glycine
D. glutamine
E. alanine
19. Phase II of xenobiotic metabolism
A. involves oxygenation catalyzed by cytochrome P450 enzymes.
B. involves conjugation reactions that result in a more water soluble product.
C. involves conjugation reactions that result in more hydrophobic products.
D. is the breakdown of phase I products in the lysosomes.
E. sometimes results in a highly reactive epoxide that can act as a carcinogen.
20. In Thalassemia, the predominant form of hemoglobin that is found is
A. alpha2beta2
B. beta4
C. beta4gamma2
D. alpha2gamma2
E. alpha2epsilon2
21. Leptin is
A. a drug sometimes called Redux
B. an appetite stimulant
C. a key weight control hormone
D. a membrane receptor
E. a protein expressed mainly in the hypothalamus
22. In vision, the role of TRANSDUCIN in the signaling process is to:
A. absorb a photon of light
B. activate guanyl cyclase
C. activate phosphodiesterase
D. deactivate rhodopsin
E. act as a channel for entry of Na+
23. An infant had profuse bleeding after his circumcision. Analysis showed an abnormally long partial thromboplastin time (PTT), but a normal prothrombin time (PT). A blood mixing study corrected the PTT time. What is the likely defect?
A. a circulating anticoagulant
B. lack of vitamin K
C. deficiency of factor VII
D. ingestion of excessive aspirin
E. deficiency of factor VIII
24. Pernicious anemia in an elderly patient is most often due to?
A. lack of intrinsic factor
B. lack of folate in the diet
C. autoimmune problem
D. deficiency in methionine
E. lack of B12 in the diet
25. The primary defect in cystic fibrosis is:
A. problem with cysteine metabolism
B. collagen defect with gly replaced by cys
C. defective cystine transport
D. defective chloride channel
E. lack of vitamin C
26. In rigor mortis, the muscle contraction process is stopped at the point where:
A. ATP is initially hydrolyzed
B. Ca++ exposes binding sites on actin
C. ADP and Pi have been released
D. the myosin head is in the "high energy" configuration
E. after Ca++ has been returned to the sarcoplasmic reticulum
27. Prions are believed to cause disease via:
A. a DNA virus
B. a misfolded protein
C. an RNA virus
D. a protein kinase
E. cytokines
28. One of the major factors implicated in most cases of Type I diabetes is:
A. genetic defect in insulin receptors
B. genetic defect in glucokinase in pancreatic cells
C. accumulation of mitochondrial DNA mutations
D. antibodies to Glutamate Decarboxylase (GAD)
E. obesity
29. Which of the following blood proteins does NOT require vitamin K to become fully functional?
A. fibrinogen
B. thrombin
C. factor IX
D. factor X
E. factor VII
30. Cyclin B is present in highest concentration during which phase of the cell cycle?
A. G1
B. G2
C. S
D. M
E. none of the above
1D 2A 3B 4C 5B 6E 7B 8A 9D 10A 11B 12E 13D 14E 15E 16A 17D 18C 19B 20D 21C 22C 23E 24A,C 25D 26C 27B 28D 29A 30D ANSWERS:
Biochemistry 520 November 12, 1996 Exam #5 NAME__________________________________________
PART II. (40 points)
I. (7 points) Shown below are graphs of O2 saturation curves for hemoglobin or myoglobin. From the list provided, select the numbered answer which best fits each binding curve. Each number must be used.
___ | / _/ /-- __/ | / A - /- ---/ | | / B -/ C ---/ D percent | / -/ --/ _/ saturated | | / / _/ with oxygen | | / / _/ |/ - / _/ || / --/ __/ || / / __/ || - --/ ____/ || / --/ ___/ || --/ _ / ___/ E ||_-/--/-___/___ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ |_____________________________________________ partial pressure of oxygen -->
A.____________________ 1. elevated 2,3 BPG
B.____________________ 2. elevated pH
C.____________________ 3. elevated CO2
D.____________________ 4. Met Hb
E.____________________ 5. Mb
6. HbF
7. HbH (4)
2. (7 points)
A. Describe the series of events that occurs at the neuromuscular junction from the arrival of the action potential at the presyneptic nerve terminus up to the detection of the chemical signal at the postsynaptic membrane and its destruction.
B. How would diisopropylfluorophosphate, or a nerve gas like sarin, affect this process?
C. One of the effects of ammonia in large concentrations is to dissipate transmembrane proton gradients. How might NH3 affect the signal transduction process at the neuromuscular junction? Explain.
3. Olfaction, the sense of smell, is a sensory system that shares common features of signal transduction with systems we have discussed in class. The interaction of odorant molecules with olfactory sensory neurons results in a change in neuronal transmembrane potential. This depolarization results in the propagation of an action potential down the axon to the olfactory bulb of the brain.
A. (9 points) In the following diagram identify the item indicated by the boxes with the correct term that will develop the currently accepted model of olfactory signal transduction.
(diagram with receptor, "G" protein, ATP --> B, E binding to G protein in exchange for F, B acting on sodium channel, a second "G" protein alpha subunit interacting with a membrane bound protein G, which releases IP3 from membrane component H. This causes opening of a second channel I.
A. _________________
B. _________________
C. _________________
D. _________________ (Generic name for this 3 subunit protein)
E. _________________ (nucleotide)
F. _________________
G. _________________
H. _________________ (substrate for G)
I. _________________ (cation normally less than micromolar levels in cytoplasm)
B. (4 points) You have recently discovered evidence that nitric oxide may also be involved in olfactory signal transduction. Diagram a scheme similar to that above which accounts for your results. Indicate what NO is synthesized from, and its specific target.
4. (6 points) IRF regulates cellular iron levels at the gene expression level. Explain how IRF can either increase or decrease cellular Fe according to need.
5. (8 points) Potato chips containing the non-digestable fat substitute, Olestra, are said to have negative nutrition value because they inhibit the absorption of some vitamins in the GI tract. Which vitamins would most likely be affected? Name one biochemical use for each vitamin.