MCB 450 Exam 1-3 UPDATED ACTUAL
QUESTIONS AND CORRECT ANSWERS
What are end products of oxidative catabolism?
a) CO_2, NH_3, H_2O
b) NADH and FADH_2
c) ATP
d) A and B
e) A, B and C - CORRECT ANSWER e) A, B and C
What occurs when a pyruvate is reduced in the presence of NADH + H^+ and lactic acid
dehydrogenase?
a) The carbon 1 (C1) carboxylate group will be cut off as a CO_2.
b) The C2 carbonyl will be converted to a hydroxyl and gain a proton.
c) The C2 carbonyl will become oxidized to make an alkene bond with C3.
d) C3 will lose a proton to create an alkene bond with C2 causing the carbonyl to open to an
oxyanion.
e) The C1 carboxylate will become linked to the enzyme through a thioester bond. - CORRECT
ANSWER b) The C2 carbonyl will be converted to a hydroxyl and gain a proton.
What is the difference between an Isomerase reaction and a Transferase reaction?
a) Transferases reverse the activities of isomerases.
b) Transferases cut carbon-carbon bonds whereas Isomerases form carbon-carbon bonds.
c) Isomerases move a functional group within a molecule whereas a Transferase moves a functional
group between two different molecules.
d) An Isomerase takes electrons whereas Transferases donate electrons.
e) They are synonymous. - CORRECT ANSWER c) Isomerases move a functional group
within a molecule whereas a Transferase moves a functional group between two different molecules.
A Thioester is more reactive compared to an ester bond due to which of the following?
a) The lack of resonance between the carbonyl oxygen and the sulfur atom
b) The facile protonation of the sulfur atom
,c) Pantothenic acid is a good leaving group
d) The strong resonance between the ketone oxygen and the sulfur atom
e) The nucleophilic potential of the sulfur atom. - CORRECT ANSWER a) The lack of
resonance between the carbonyl oxygen and the sulfur atom
The binding energy of an Enzyme - Substrate interaction is the sum of which of the following?
a) Energies from strong bonds such as H-bonds, hydrophobic and ionic interactions
b) Energies from weak covalent bonds such as disulfide bonds
c) Lock and key binding heat absorption.
d) Electrostatic van der Waals interaction energies.
e) Energies from weak interactions such as hydrogen bonds, ionic and hydrophobic interactions. -
CORRECT ANSWER e) Energies from weak interactions such as hydrogen bonds, ionic and
hydrophobic interactions.
In a Michaelis-Menten graph, what does the Km represent?
a) The Km is ½ of the Vmax and represents the binding affinity of the substrate-enzyme interaction
b) It is the maximum rate of the reaction
c) The entropy of the reaction
d) The reaction has reached equilibrium
e) The $\Delta G$ of the reaction is positive - CORRECT ANSWER a) The Km is ½ of the
Vmax and represents the binding affinity of the substrate-enzyme interaction
What occurs during reversible competitive inhibition of an enzyme?
a) The apparent Km increases while the Vmax is unaltered.
b) Both Km and Vmax values are decreased.
c) The apparent Km is unaffected, and the Vmax is enhanced.
d) The apparent Km increases and the Vmax is reduced.
e) The apparent Km and Vmax values are increased. - CORRECT ANSWER a) The apparent
Km increases while the Vmax is unaltered.
Ibuprofen is a reversible inhibitor. How does it inhibit COX?
,a) Ibuprofen reacts with a Serine in the catalytic pocket of COX to form a covalent bond and inhibit
enzyme activity.
b) Ibuprofen non-covalently interacts with the key Serine in COX to block substrate access.
c) Ibuprofen binds to the COX substrate to block the enzyme.
d) Ibuprofen binds to an allosteric binding site to alter the COX active site affinity for arachidonic
acid.
e) Ibuprofen binds to a non-competitive site to prevent COX-arachidonic acid interactions from
reacting. - CORRECT ANSWER b) Ibuprofen non-covalently interacts with the key Serine in
COX to block substrate access.
What is the role of an Arginine finger in a classic ATPase binding pocket?
a) The hydrophobic nature of Arg attracts the ATP gamma phosphate.
b) The negative charge of the Arg side chain binds with Mg^{2+} to organize it with the beta and
gamma phosphates of ATP.
c) The positive charge of the Arg side chain interacts with the negative charge of the ATP gamma
phosphate.
d) The Arg side chain deprotonates water to create a nucleophile.
e) The Arg side chain interacts with the ribose ring of ATP. - CORRECT ANSWER c) The
positive charge of the Arg side chain interacts with the negative charge of the ATP gamma phosphate.
Which of the following statements about integral membrane proteins is FALSE?
a) They sometimes consist of beta-sheets that curl up to form a hollow cylinder that serves as a pore in
the membrane.
b) Membrane proteins with one or more transmembrane alpha helix/helices may have functional
domains on both sides of the membrane.
c) They can be released from membranes by treatments that break hydrogen bonds or interfere with
electrostatic interactions.
d) They can be glycosylated.
e) Formation of membrane-spanning alpha helices is favored when the amino acid chain is surrounded
by membrane fatty acyl chains and there are no water molecules with which peptide groups can form
hydrogen bonds. - CORRECT ANSWER c) They can be released from membranes by
treatments that break hydrogen bonds or interfere with electrostatic interactions.
Which of the following statements about Primary Active membrane transport is true?
a) Particles move in opposite directions down an electrochemical gradient.
, b) Gases diffuse through membranes without the use of a membrane transporter.
c) Uses ATP hydrolysis to move particles down an electrochemical gradient.
d) Uses ATP hydrolysis to move particles against an electrochemical gradient.
e) Uses ATP hydrolysis to move oxygen across membranes. - CORRECT ANSWER d) Uses
ATP hydrolysis to move particles against an electrochemical gradient.
Which of the following lipid properties affect membrane fluidity?
a) Acyl chain saturation
b) The charge on the hydrophilic head group
c) Cholesterol content
d) A and B
e) A and C - CORRECT ANSWER e) A and C
Which of the following is a second messenger of hormone action?
a) cAMP
b) Phospholipase C
c) Diacylglycerol (DAG)
d) A and B
e) A and C - CORRECT ANSWER e) A and C
How does heterotrimeric G-protein (HGP) activation lead to calcium release from the ER?
a) GTP bound HGP activates phospholipase C (PLC) which cleaves phosphoinositide 4,5
bisphosphate (PIP_2) to release IP_3. IP_3 binds to its receptor on the ER leading to calcium release.
b) GDP bound HGP activates phospholipase C (PLC) which cleaves phosphoinositide 4,5
bisphosphate (PIP_2) to release IP_3. IP_3 binds to its receptor on the Golgi leading to calcium
release.
c) GTP bound HGP activates protein kinase A (PKA) which cleaves phosphoinositide 3,4,5
bisphosphate (PIP_3) to release IP_4. IP_4 binds to its receptor on the ER leading to calcium release.
d) GTP bound HGP activates phospholipase A (PLA) which cleaves phosphoinositide 4,5
bisphosphate (PIP_2) to release a lysolipid that binds to its receptor on the ER leading to calcium
release. - CORRECT ANSWER a) GTP bound HGP activates phospholipase C (PLC) which
cleaves phosphoinositide 4,5 bisphosphate (PIP_2) to release IP_3. IP_3 binds to its receptor on the
ER leading to calcium release.
QUESTIONS AND CORRECT ANSWERS
What are end products of oxidative catabolism?
a) CO_2, NH_3, H_2O
b) NADH and FADH_2
c) ATP
d) A and B
e) A, B and C - CORRECT ANSWER e) A, B and C
What occurs when a pyruvate is reduced in the presence of NADH + H^+ and lactic acid
dehydrogenase?
a) The carbon 1 (C1) carboxylate group will be cut off as a CO_2.
b) The C2 carbonyl will be converted to a hydroxyl and gain a proton.
c) The C2 carbonyl will become oxidized to make an alkene bond with C3.
d) C3 will lose a proton to create an alkene bond with C2 causing the carbonyl to open to an
oxyanion.
e) The C1 carboxylate will become linked to the enzyme through a thioester bond. - CORRECT
ANSWER b) The C2 carbonyl will be converted to a hydroxyl and gain a proton.
What is the difference between an Isomerase reaction and a Transferase reaction?
a) Transferases reverse the activities of isomerases.
b) Transferases cut carbon-carbon bonds whereas Isomerases form carbon-carbon bonds.
c) Isomerases move a functional group within a molecule whereas a Transferase moves a functional
group between two different molecules.
d) An Isomerase takes electrons whereas Transferases donate electrons.
e) They are synonymous. - CORRECT ANSWER c) Isomerases move a functional group
within a molecule whereas a Transferase moves a functional group between two different molecules.
A Thioester is more reactive compared to an ester bond due to which of the following?
a) The lack of resonance between the carbonyl oxygen and the sulfur atom
b) The facile protonation of the sulfur atom
,c) Pantothenic acid is a good leaving group
d) The strong resonance between the ketone oxygen and the sulfur atom
e) The nucleophilic potential of the sulfur atom. - CORRECT ANSWER a) The lack of
resonance between the carbonyl oxygen and the sulfur atom
The binding energy of an Enzyme - Substrate interaction is the sum of which of the following?
a) Energies from strong bonds such as H-bonds, hydrophobic and ionic interactions
b) Energies from weak covalent bonds such as disulfide bonds
c) Lock and key binding heat absorption.
d) Electrostatic van der Waals interaction energies.
e) Energies from weak interactions such as hydrogen bonds, ionic and hydrophobic interactions. -
CORRECT ANSWER e) Energies from weak interactions such as hydrogen bonds, ionic and
hydrophobic interactions.
In a Michaelis-Menten graph, what does the Km represent?
a) The Km is ½ of the Vmax and represents the binding affinity of the substrate-enzyme interaction
b) It is the maximum rate of the reaction
c) The entropy of the reaction
d) The reaction has reached equilibrium
e) The $\Delta G$ of the reaction is positive - CORRECT ANSWER a) The Km is ½ of the
Vmax and represents the binding affinity of the substrate-enzyme interaction
What occurs during reversible competitive inhibition of an enzyme?
a) The apparent Km increases while the Vmax is unaltered.
b) Both Km and Vmax values are decreased.
c) The apparent Km is unaffected, and the Vmax is enhanced.
d) The apparent Km increases and the Vmax is reduced.
e) The apparent Km and Vmax values are increased. - CORRECT ANSWER a) The apparent
Km increases while the Vmax is unaltered.
Ibuprofen is a reversible inhibitor. How does it inhibit COX?
,a) Ibuprofen reacts with a Serine in the catalytic pocket of COX to form a covalent bond and inhibit
enzyme activity.
b) Ibuprofen non-covalently interacts with the key Serine in COX to block substrate access.
c) Ibuprofen binds to the COX substrate to block the enzyme.
d) Ibuprofen binds to an allosteric binding site to alter the COX active site affinity for arachidonic
acid.
e) Ibuprofen binds to a non-competitive site to prevent COX-arachidonic acid interactions from
reacting. - CORRECT ANSWER b) Ibuprofen non-covalently interacts with the key Serine in
COX to block substrate access.
What is the role of an Arginine finger in a classic ATPase binding pocket?
a) The hydrophobic nature of Arg attracts the ATP gamma phosphate.
b) The negative charge of the Arg side chain binds with Mg^{2+} to organize it with the beta and
gamma phosphates of ATP.
c) The positive charge of the Arg side chain interacts with the negative charge of the ATP gamma
phosphate.
d) The Arg side chain deprotonates water to create a nucleophile.
e) The Arg side chain interacts with the ribose ring of ATP. - CORRECT ANSWER c) The
positive charge of the Arg side chain interacts with the negative charge of the ATP gamma phosphate.
Which of the following statements about integral membrane proteins is FALSE?
a) They sometimes consist of beta-sheets that curl up to form a hollow cylinder that serves as a pore in
the membrane.
b) Membrane proteins with one or more transmembrane alpha helix/helices may have functional
domains on both sides of the membrane.
c) They can be released from membranes by treatments that break hydrogen bonds or interfere with
electrostatic interactions.
d) They can be glycosylated.
e) Formation of membrane-spanning alpha helices is favored when the amino acid chain is surrounded
by membrane fatty acyl chains and there are no water molecules with which peptide groups can form
hydrogen bonds. - CORRECT ANSWER c) They can be released from membranes by
treatments that break hydrogen bonds or interfere with electrostatic interactions.
Which of the following statements about Primary Active membrane transport is true?
a) Particles move in opposite directions down an electrochemical gradient.
, b) Gases diffuse through membranes without the use of a membrane transporter.
c) Uses ATP hydrolysis to move particles down an electrochemical gradient.
d) Uses ATP hydrolysis to move particles against an electrochemical gradient.
e) Uses ATP hydrolysis to move oxygen across membranes. - CORRECT ANSWER d) Uses
ATP hydrolysis to move particles against an electrochemical gradient.
Which of the following lipid properties affect membrane fluidity?
a) Acyl chain saturation
b) The charge on the hydrophilic head group
c) Cholesterol content
d) A and B
e) A and C - CORRECT ANSWER e) A and C
Which of the following is a second messenger of hormone action?
a) cAMP
b) Phospholipase C
c) Diacylglycerol (DAG)
d) A and B
e) A and C - CORRECT ANSWER e) A and C
How does heterotrimeric G-protein (HGP) activation lead to calcium release from the ER?
a) GTP bound HGP activates phospholipase C (PLC) which cleaves phosphoinositide 4,5
bisphosphate (PIP_2) to release IP_3. IP_3 binds to its receptor on the ER leading to calcium release.
b) GDP bound HGP activates phospholipase C (PLC) which cleaves phosphoinositide 4,5
bisphosphate (PIP_2) to release IP_3. IP_3 binds to its receptor on the Golgi leading to calcium
release.
c) GTP bound HGP activates protein kinase A (PKA) which cleaves phosphoinositide 3,4,5
bisphosphate (PIP_3) to release IP_4. IP_4 binds to its receptor on the ER leading to calcium release.
d) GTP bound HGP activates phospholipase A (PLA) which cleaves phosphoinositide 4,5
bisphosphate (PIP_2) to release a lysolipid that binds to its receptor on the ER leading to calcium
release. - CORRECT ANSWER a) GTP bound HGP activates phospholipase C (PLC) which
cleaves phosphoinositide 4,5 bisphosphate (PIP_2) to release IP_3. IP_3 binds to its receptor on the
ER leading to calcium release.
