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Bio302 Biochemistry II Midterm Examination I, March 31st, 2005 Answer all the questions from 1-8 (each 5 points) But answer only 6 of the 7 questions among questions 9-15 (each 10 points) Question 1 (5 points) Which of the following are the second messengers that are produced by the phosphoinositide cascade? a) Phosphatidyl inositol 4,5-bisphosphate b) Inositol 1,3,4-trisphosphate c) Inositol 1,4,5-trisphosphate d) Inositol 4-phosphaıte e) Inositol 1,3,4,5-tetraksphosphate f) Diacylglycerol Question 2. (5 points) True or false? Receptor tyrosine kinases a) integral membrane enzymes. b) are often activated by ligand-induced dimerization c) can phosphorylate themselves on their cytoplasmic domains when activated by their ligands d) are seven-helix transmembrane receptors. e) activate their targets via G proteins. Question 3. (5 points) Which of the following enzymes have impaired activity in vitamin B1 deficiency? a) succinate dehydrogenase b) pyruvate dehydrogenase c) isocitrate dehydrogenase d) a-ketoglutarate dehydrogenase e) dihydrolipoyl trasacetylase Question 4. (5 points) Conversion of citrate to isocitrate is a type of ............. reaction. a) oxidation b) isomerization c) condensation d) ligation e) none of the above Question 5. (5 points) Beri-beri is caused by a deficiency of................................. a) riboflavin b) pantothenic acid c) thiamine d) all of the above e) none of the above Question 6. (5 points) Metabolite required to convert 3-phosphoglycerate to 2phosphoglycerate is a) 1-phophogycerate b) diacylglycerol c) NADH d) 2,3-bisphosphogycerate e) 1,3-bisphospogycerate Question 7. (5 points). What is the structural feature common to ATP, FAD, NAD+ and coenzymeA? Question 8. (5 points). Since lactate is a “dead-end” product of metabolism in the sense that its sole fate is to be re-converted into pyruvate, what is the purpose of its formation? OBS! Chose 6 of the 7 questions below!!!!!! Question 9. (10 points) What evidences might implicate that cAMP is a second messenger? Question 10. (10 points) Explain how the action of a single hormone molecule can be “amplified”. Give an example. Question 11. (10 points) Explain how calmodulin serves as a calcium sensor in most eukaryotic cells. Describe how calmodulin activates target proteins. Give an example. Question 12. (10 points) What is the effect of increasing the concentration of each of the following metabolites on the net rate of glycolysis. Briefly explain each answer. a) glucose 6-phosphate: b) fructose 1,6-bisphosphate: c) fructose 2,6-bisphosphate: d) citrate Question 13. (10 points) What are the two metabolic products formed from pyruvate in yeast which turns grape juice into champagne? Name the two enzymes involved in this reaction. Question 14. (10 points) What is the purpose of hexokinase variants in different mammalian cells? Liver has a variant of hexokinase, known also as glucokinase (or hexokinase IV) a monomeric protein which shows sigmoidal kinetics in contrast to other hexokinases which obey Michaelis-Menten kinetics. Explain the purpose of this variation. Question 15 (10 points) Inside cells G’ value for the hydrolysis of ATP to ADP+Pi is appoximately -12 kcal/mol (standard free energy change for this reaction is Go’= -7.3 kcal/mol). Calculate the expected ratio of [ATP] to [ADP+Pi] found in cells at 37oC. (Gas constant R= 1.987 cal.M-1K-1, K=oC+273.15)