BCH 369 TEST 3 QUESTIONS WITH
ALL ANSWERS CERTIFIED
Two species of bacteria have been isolated, one from a hot spring (average
temperature 50°C) and another from a glacial lake (average temperature 4°C). Which of
the following statements about the
membrane composition of the "hot" and "cold" species is most likely CORRECT?
A) Lipids from "hot" membranes contain a greater proportion of longer-chain fatty acids
than lipids from "cold" membranes.
B) Lipids from "hot" membranes contain a greater proportion of unsaturated fatty acids
than lipids from "cold" membranes.
C) Membranes from "cold" bacteria will contain more cholesterol than membranes from
"hot" bacteria.
D) At 27°C, "hot" membranes will be more fluid than "cold" membranes.
E) Lipids from "hot" membranes will contain more glycerophospholipids than lipids from
"cold" membranes. - Answer-A) Lipids from "hot" membranes contain a greater
proportion of longer-chain fatty acids than lipids from "cold" membranes.
Which of the following methods of altering enzyme activity is irreversible?
A) Binding of transition state analogs to enzymes.
D) Phosphorylation of enzymes.
B) Binding of competitive inhibitors to enzymes.
E) None of the above.
C) Binding of allosteric effectors to enzymes. - Answer-E) None of the above.
E. coli ribonuclease HI is an enzyme that catalyzes the hydrolysis of phosphodiester
bonds in RNA. The active site is shown below. The pK values for all of the His residues
in ribonuclease HI were determined and include values of 7.1, 5.5, and <5.0 (less than
5.0). Which value is most likely to correspond to His124?
A) <5.0 B) 5.5 C) 7.1 - Answer-A) <5.0
When a slice of apple is exposed to air, it quickly turns brown. This is due to the
enzymatic activity of catechol oxidase, which catalyzes the oxidation of phenols in the
apple to dark-colored products. The enzyme catalyzed reaction scheme is given below.
The compounds p-hydroxybenzoic acid (PHBA) and phenylthiourea (PTU) are known to
be inhibitors of the above reaction (structures below).
Catechol oxidase has a native KM for catechol of 0.3 mM and a Vmax of 196 µM/min,
with a KI for PHBA of 0.15 mM. Calculate the initial velocity (v0) expected (µM/min)
when the catechol oxidase assay is conducted using 0.4 mM of catechol in the
presence of 0.13 mM PHBA.
A) 81.7 mM/min B) 81.7 µM/min C) 112 µM/min D) 75.0 µM/min E) 0.112 mM/min -
Answer-B) 81.7 µM/min
Calculate the free energy change for the movement of Na+ into a depolarized nerve cell
, at a potential of +50 mV when the ratio of [Na+]in/[Na+]out = 7.3. Assume the
temperature is 37oC. Is this process
favorable?
A) -9.95 kJ/mol; favorable
D) -7.05 kJ/mol; favorable
B) +9.95 kJ/mol; unfavorable
E) +0.300 kJ/mol; unfavorable
C) +7.05 kJ/mol; unfavorable - Answer-B) +9.95 kJ/mol; unfavorable
When secreted in the human body, the hormone glucagon causes rapid degradation of
glycogen in liver cells. This mobilization of glycogen is accomplished though a signaling
pathway. What is the proper temporal sequence of the following steps in this reaction
cascade?1 - displacement of GDP with GTP on the α-subunit of the G-protein2 -
phosphorolysis of glycogen3 - dissociation of the regulatory subunits activates protein
kinase A4 - phosphorylation of glycogen phosphorylase5 - glucagon binds to a specific,
transmembrane receptor6 - formation of cyclic-AMP by adenylate cyclase
A) 5-1-6-3-4-2 B) 5-1-6-3-2-4 C) 5-3-1-6-4-2 D) 5-6-1-3-4-2 E) 5-3-1-6-2-4 - Answer-A)
5-1-6-3-4-2
Which of the following accurately describes the lipid bilayer in biological membranes?
A) The bilayer is stabilized by hydrophilic interactions between the polar lipid head
groups and the aqueous environment.
B) Integral membrane proteins enhance the stability of membrane lipid bilayers.
C) The thickness of membrane bilayers varies slightly, depending on the fatty acids
incorporated in the lipids.
D) Individual lipid molecules flip-flop rapidly between leaflets of the bilayer. - Answer-C)
The thickness of membrane bilayers varies slightly, depending on the fatty acids
incorporated in the lipids
Which of the following would REDUCE a hormone signal mediated via the G protein
signal transduction system?
A) Addition of a substance that activates protein phosphatases.
B) Addition of a substance that inhibits phosphodiesterase.
C) Addition of a substance that activates adenylate cyclase.
D) A and C - Answer-A) Addition of a substance that activates protein phosphatases.
Phorbol esters, which are compounds isolated from plants, are structurally similar to
diacylglycerol. How does the addition of phorbol esters affect the signaling pathways of
cells in culture?
A) They would elevate the concentration of cAMP.
B) They would activate protein kinase A.
C) They would activate protein kinase C.
D) They would activate Ras protein.
E) They would stimulate lipid hormone signaling. - Answer-C) They would activate
protein kinase C.
Which of the following statements is/are TRUE regarding the molecule shown?
1. This molecule is a membrane lipid.2. This molecule contains a carbon-carbon double
bond.3. This molecule is unsaturated.
A) 1 and 2 B) 1 and 3 C) 2 and 3 D) 1, 2 and 3 - Answer-C) 2 and 3
ALL ANSWERS CERTIFIED
Two species of bacteria have been isolated, one from a hot spring (average
temperature 50°C) and another from a glacial lake (average temperature 4°C). Which of
the following statements about the
membrane composition of the "hot" and "cold" species is most likely CORRECT?
A) Lipids from "hot" membranes contain a greater proportion of longer-chain fatty acids
than lipids from "cold" membranes.
B) Lipids from "hot" membranes contain a greater proportion of unsaturated fatty acids
than lipids from "cold" membranes.
C) Membranes from "cold" bacteria will contain more cholesterol than membranes from
"hot" bacteria.
D) At 27°C, "hot" membranes will be more fluid than "cold" membranes.
E) Lipids from "hot" membranes will contain more glycerophospholipids than lipids from
"cold" membranes. - Answer-A) Lipids from "hot" membranes contain a greater
proportion of longer-chain fatty acids than lipids from "cold" membranes.
Which of the following methods of altering enzyme activity is irreversible?
A) Binding of transition state analogs to enzymes.
D) Phosphorylation of enzymes.
B) Binding of competitive inhibitors to enzymes.
E) None of the above.
C) Binding of allosteric effectors to enzymes. - Answer-E) None of the above.
E. coli ribonuclease HI is an enzyme that catalyzes the hydrolysis of phosphodiester
bonds in RNA. The active site is shown below. The pK values for all of the His residues
in ribonuclease HI were determined and include values of 7.1, 5.5, and <5.0 (less than
5.0). Which value is most likely to correspond to His124?
A) <5.0 B) 5.5 C) 7.1 - Answer-A) <5.0
When a slice of apple is exposed to air, it quickly turns brown. This is due to the
enzymatic activity of catechol oxidase, which catalyzes the oxidation of phenols in the
apple to dark-colored products. The enzyme catalyzed reaction scheme is given below.
The compounds p-hydroxybenzoic acid (PHBA) and phenylthiourea (PTU) are known to
be inhibitors of the above reaction (structures below).
Catechol oxidase has a native KM for catechol of 0.3 mM and a Vmax of 196 µM/min,
with a KI for PHBA of 0.15 mM. Calculate the initial velocity (v0) expected (µM/min)
when the catechol oxidase assay is conducted using 0.4 mM of catechol in the
presence of 0.13 mM PHBA.
A) 81.7 mM/min B) 81.7 µM/min C) 112 µM/min D) 75.0 µM/min E) 0.112 mM/min -
Answer-B) 81.7 µM/min
Calculate the free energy change for the movement of Na+ into a depolarized nerve cell
, at a potential of +50 mV when the ratio of [Na+]in/[Na+]out = 7.3. Assume the
temperature is 37oC. Is this process
favorable?
A) -9.95 kJ/mol; favorable
D) -7.05 kJ/mol; favorable
B) +9.95 kJ/mol; unfavorable
E) +0.300 kJ/mol; unfavorable
C) +7.05 kJ/mol; unfavorable - Answer-B) +9.95 kJ/mol; unfavorable
When secreted in the human body, the hormone glucagon causes rapid degradation of
glycogen in liver cells. This mobilization of glycogen is accomplished though a signaling
pathway. What is the proper temporal sequence of the following steps in this reaction
cascade?1 - displacement of GDP with GTP on the α-subunit of the G-protein2 -
phosphorolysis of glycogen3 - dissociation of the regulatory subunits activates protein
kinase A4 - phosphorylation of glycogen phosphorylase5 - glucagon binds to a specific,
transmembrane receptor6 - formation of cyclic-AMP by adenylate cyclase
A) 5-1-6-3-4-2 B) 5-1-6-3-2-4 C) 5-3-1-6-4-2 D) 5-6-1-3-4-2 E) 5-3-1-6-2-4 - Answer-A)
5-1-6-3-4-2
Which of the following accurately describes the lipid bilayer in biological membranes?
A) The bilayer is stabilized by hydrophilic interactions between the polar lipid head
groups and the aqueous environment.
B) Integral membrane proteins enhance the stability of membrane lipid bilayers.
C) The thickness of membrane bilayers varies slightly, depending on the fatty acids
incorporated in the lipids.
D) Individual lipid molecules flip-flop rapidly between leaflets of the bilayer. - Answer-C)
The thickness of membrane bilayers varies slightly, depending on the fatty acids
incorporated in the lipids
Which of the following would REDUCE a hormone signal mediated via the G protein
signal transduction system?
A) Addition of a substance that activates protein phosphatases.
B) Addition of a substance that inhibits phosphodiesterase.
C) Addition of a substance that activates adenylate cyclase.
D) A and C - Answer-A) Addition of a substance that activates protein phosphatases.
Phorbol esters, which are compounds isolated from plants, are structurally similar to
diacylglycerol. How does the addition of phorbol esters affect the signaling pathways of
cells in culture?
A) They would elevate the concentration of cAMP.
B) They would activate protein kinase A.
C) They would activate protein kinase C.
D) They would activate Ras protein.
E) They would stimulate lipid hormone signaling. - Answer-C) They would activate
protein kinase C.
Which of the following statements is/are TRUE regarding the molecule shown?
1. This molecule is a membrane lipid.2. This molecule contains a carbon-carbon double
bond.3. This molecule is unsaturated.
A) 1 and 2 B) 1 and 3 C) 2 and 3 D) 1, 2 and 3 - Answer-C) 2 and 3
