Download Midterm Examination I, March 31st, 2005

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)