Download Question 2. Which of the following statements about G proteins are

Bio 302 Biochemistry II
Midterm Examination I, March 31st, 2004
Questions 1-10 each 5 points, questions 11-15 each 10 points.
Question 1. Match the four cofactors in the left column with the appropriate
structural features and properties from the right column.
a) ATP
1) nicotinamide ring
b) FAD
2) adenine group
c) NAD+
3) isoalloxazine ring
d) CoA
4) acyl group transfer
5) electron transfer
6) phosphate transfer
Question 2. Which of the following statements about G proteins are correct?
a) G proteins are activated by twelve-membrane receptors only
b) G proteins make up a large family of proteins that are involved in
regulating enzymes, chemotaxis, visual excitation, and ion channels.
c) G proteins cycle between a GTP form and an GDP form by means of a selfcatalyzed exchange reaction.
d) Activated seven-helix proteins switch them on by causing the exchange of
GTP for GDP.
e) Certain G protein can participate in a reaction with NAD+ that leads to
their covalent modification, for example, reactions catalyzed by cholera
and pertussis toxins.
Question 3. Which of the following are the second messengers that are
produced by the phosphoinositide cascade?
a) Diacylglyerol (DAG).
b) Inositol 4-phosphate.
c) Inositol 1,3,4,5-tetrakisphosphate.
d) Phosphatidyl inositol 4,5-bisphosphate (PIP2).
f) Inositol 1,4,5-trisphosphate (IP3)
Question 4. Which of the following statements about cyclicAMP are correct?
a) ATP is converted to cyclicAMP by the enzyme adenylate cyclase in one
step.
b) Cyclic AMP is converted to 5’-AMP by a phosphodiesterase-catalayzed
reaction with H2O.
c) Cyclic AMP binds the catalytic subunits of protein kinase A and
activates the enzyme allosterically.
d) Cyclic AMP interacts with a hormone-receptor complexş to dissociate
the hormone.
e) The hormone receptor complex enters the cell and affects the activities
of target enzymes.
Question 5. Which of the following answer complete the sentence correctly?
The reactions catalyzed by phosphofructokinase and by pyruvate kinase are
similar in that
a) both involve a "high-energy" sugar derivative
b) both are essentially irreversible
c) both generate ATP
d) both involve three-carbon compounds
e) neither of the above
Question 6. When blood glucose levels are low, glucagon is secreted. Which
of the following are the effects of increased glucaogon levels on glycolysis and
related reactions in liver?
a) Phosphofructokinase is activated.
b) Phosphofructokinase in inhibited.
c) Fructose bisphospatase 2 is activated.
d) Fructose bisphosphatase 2 is inhibited.
e) Glycolysis is accelerated.
f) Glycolysis is slowed down.
Question 7. Which of the following answer complete the sentence correctly?
The reactions catalyzed by phosphofructokinase and by pyruvate kinase are
similar in that
a) both involve a "high-energy" sugar derivative
b) both are essentially irreversible
c) both generate ATP
d) both involve three-carbon compounds
e) neither of the above
Question 8. Lactase deficiency is characterized by the inability to hydrolize
a) -1,4 glucosidic bonds.
b) -1,6 glucosidic bonds.
c) -1,4 glucosidic bonds.
d) -1,6 glucosidic bonds.
e) -1,4 galactosidic bonds.
Question 9. Which of the following statements about glucose transporters are
true?
a) They are transmembrane proteins
b) They accomplish the movement of glucose across animal cell plasma
membranes
c) Their tissue distribution and concentration can depend on the tissue
type and metabolic state of the organism
d) They constitute a protein family of five isoforms.
Question 10. State whether true or false.
a) Receptor tyrosine kinases activate their targets via the G protein
cascade.
b) Receptor tyrosine kinases can phosphorylate themselves on their
cytoplasmic domains when activated.
c) Receptor tyrosine kinases that have been activated by hormone
binding are recognized by target proteins having SH2 (scr protein
homology region 2) sequences.
d) Some oncogenes encode tyrosine kinases.
e) Epidermal growth factor (EGF) is a protein kinase that phosphorylates
tyrosine residues.
Question 11. For the hydrolysis of ATP to ADP + Pi, the standard free energy
change is Go’=–7.3 kcal/mol. However, inside cells the G value for the
hydrolysis of ATP to ADP +Pi is approximately –12 kcal/mol. Use this
information to calculate the approximate ratio of [ATP] to [ADP][Pi] found in
cells at 37oC. (Gas constant,R= 1.987 cal/mol.oK)
Question 12.
An uncharged molecule is transported from side 1 to side 2 of a membrane.
It’s concentration is 10-1 M on side 1 and 10-4 M on side 2. Will the transport be
an active or a passive process? Explain your answer.
(Gas constant,R= 1.987 cal/mol.oK)
Question 13.
The potassium channel is over 100 times more permeable to potassium than
to sodium. Explain the molecular mechanism for this selectivity.
Question 14.
Explain how the action of a single hormone molecule can be “amplified”.
Give an example.
Question 15.
Explain how calmodulin serves as a calcium sensor in most eukaryotic cells.