BIOC 384 EXAM 3 QUESTIONS &
SOLUTIONS
Which state of glycogen phosphorylase gives the enzyme its highest activity? -
ANSWERphosphorylated glycogen phosphorylase
Observe the ribbon structure of pepsin. To do this, click the green-outlined box at the
bottom of the player. Green x's will appear over your selection. Then go to the
dropdown menu and on the "Display" line, click the "Toggle Ribbon for selection" icon.
Then click the "Toggle CPK for selection" icon to remove the space-filling display. To
remove the green x's, click "Clear Selection" on the "Misc" line of the dropdown menu.
Determine the relative proportions of secondary and quaternary structure(s). What best
describes these structures? - ANSWERThe major secondary structures are beta
sheets, and there is no quaternary structure.
The catalytic acitivity and/or conformational stability of this protein is likely dependent
upon ____________ of peripheral amino acid side chains. These side chains are
expected to have a ______________ value. - ANSWERprotonation
low pKa
Which of the following correctly describes the biochemistry of the amino acids at the
termini of pepsin? - ANSWERtwo nonpolar amino acids at the N-terminus and one polar
amino acid at the C-terminus
Competitive Inhibitor - ANSWERDoes not affect the vmax of the reaction
Binds to the active site of an enzyme
Higher concentrations of substrate can reduce the effect of the inhibitor.
The y-axis intercept of the Lineweaver-Burk plot remains the same with or without this
inhibitor.
Uncompetitive Inhibitor - ANSWERDoes not bind to the free enzyme
Increasing inhibitor concentration decreases both the vmax and the Km.
Mixed Inhibitor - ANSWERDoes not bind to the active site of an enzyme, but can bind to
the free enzyme or the enzyme-substrate complex
Kinase enzymes phosphorylate other proteins and enzymes. This is a common
mechanism of covalently modifying enzymes in order to control their catalytic efficiency.
,Which of the following amino acids is not targeted for phosphorylation by kinases? -
ANSWERleucine
Which of the following activates a zymogen?
Enterokinase, Trypsinogen, Chymotrypsinogen, Pepsinogen - ANSWEREnterokinase
Choose the correct statements about the function and activity of arrestin. -
ANSWERPKA phosphorylation also modifies GPCR, leading to arrestin binding to the
receptor for endosomal transport.
Arrestin facilitates protein transport, which prevents a receptor from reassociating with
the G protein complex.
Tasting involves many different cell-signaling processes that ultimately generate nerve
signals transduced by membrane depolarization. Sweet tastes result in PIP2 hydrolysis,
while salty tastes allow sodium ions to directly alter the membrane potential. What can
you deduce about the signaling mechanisms for sweet and salty? - ANSWERSodium
ions directly enter the cells, indicating the signal is transduced by an ion channel.
Sweet utilizes the GPCR signaling pathway, activating phospholipase C.
You have a mystery hormone (agonist), and to test the nature of the agonist you add it
to a dish of cultured liver cells. Shortly afterward you observe an increase in protein
kinase activity. In a second experiment, you find the kinase is inhibited if you add an
adenylate cyclase inhibitor to the cells prior to adding your mystery agonist. Which kind
of receptor system is the agonist signaling through? - ANSWERGPCR
Glucagon binding to the glucagon receptor inhibits which of the following processes? -
ANSWERGlycogen synthesis
While glucagon (a peptide) and epinephrine (a tyrosine derivative) are very different
agonists, both signal through GPCR systems. Some of the components of the pathways
are unique, while other signaling components are shared between both systems. Place
each item in the appropriate category: glucagon and epinephrine shared, glucagon
independent, or epinephrine independent.
Shared:
Glucagon Independent:
Epinephrine Independent: - ANSWERShared:
Net accumulation of glucose
Adenylate cyclase activation
Gsa activation
cAMP signaling pathways
, Glucagon:
Peptide binding to GPCR receptor
Epinephrine:
Ligand binding to adrenergic receptor
Activation of phospholipase C
Gqa activation
When ATCase is in the __________ state it indicates that ____________ is bound, and
that ATCase is ______________ regulated. - ANSWERT; CTP; down
Consider the reaction shown below
(A) Identify the kind of chemical catalysis
(B) Identify which of the amino acids can act as X in the reaction
Choose ONE correct answer for each (A and B). - ANSWERAcid-Base catalysis
TYR
Which of the following are characteristics of allosteric enzymes such as aspartate
transcarbamoylase. There are only three correct answers. - ANSWEROften have a
sigmoidal (S-shaped) curve of Vo versus [S].
Undergo conformational changes between the R and T state.
Can have a regulatory subunit and catalytic subunit.
Signaling activity of G proteins is controlled by GTPase activating proteins (GAPs) and
Guanine exchange factors (GEFs). What are the mechanisms by which GAPs and
GEFs control G proteins (GPs)? - ANSWERGAPs inhibit GPs by stimulating GTP
hydrolysis; GEFs activate GPs by stimulating GDP-GTP exchange.
Acetylcholinesterase is an important enzyme in the nervous system.
Acetylcholinesterase activity is blocked by the nerve agent sarin gas, which forms a
covalent bond with a Ser in the active site of the enzyme. Sarin gas is a(n) -
ANSWERirreversible inhibitor
Which of the following are characteristics of allosteric enzymes like ATCase? Choose
the THREE that apply. Allosteric enzymes: - ANSWERtend to have a sigmoidal (S-
shaped) curve of V0 vs. [S].
interconvert between a more active form and less active form.
SOLUTIONS
Which state of glycogen phosphorylase gives the enzyme its highest activity? -
ANSWERphosphorylated glycogen phosphorylase
Observe the ribbon structure of pepsin. To do this, click the green-outlined box at the
bottom of the player. Green x's will appear over your selection. Then go to the
dropdown menu and on the "Display" line, click the "Toggle Ribbon for selection" icon.
Then click the "Toggle CPK for selection" icon to remove the space-filling display. To
remove the green x's, click "Clear Selection" on the "Misc" line of the dropdown menu.
Determine the relative proportions of secondary and quaternary structure(s). What best
describes these structures? - ANSWERThe major secondary structures are beta
sheets, and there is no quaternary structure.
The catalytic acitivity and/or conformational stability of this protein is likely dependent
upon ____________ of peripheral amino acid side chains. These side chains are
expected to have a ______________ value. - ANSWERprotonation
low pKa
Which of the following correctly describes the biochemistry of the amino acids at the
termini of pepsin? - ANSWERtwo nonpolar amino acids at the N-terminus and one polar
amino acid at the C-terminus
Competitive Inhibitor - ANSWERDoes not affect the vmax of the reaction
Binds to the active site of an enzyme
Higher concentrations of substrate can reduce the effect of the inhibitor.
The y-axis intercept of the Lineweaver-Burk plot remains the same with or without this
inhibitor.
Uncompetitive Inhibitor - ANSWERDoes not bind to the free enzyme
Increasing inhibitor concentration decreases both the vmax and the Km.
Mixed Inhibitor - ANSWERDoes not bind to the active site of an enzyme, but can bind to
the free enzyme or the enzyme-substrate complex
Kinase enzymes phosphorylate other proteins and enzymes. This is a common
mechanism of covalently modifying enzymes in order to control their catalytic efficiency.
,Which of the following amino acids is not targeted for phosphorylation by kinases? -
ANSWERleucine
Which of the following activates a zymogen?
Enterokinase, Trypsinogen, Chymotrypsinogen, Pepsinogen - ANSWEREnterokinase
Choose the correct statements about the function and activity of arrestin. -
ANSWERPKA phosphorylation also modifies GPCR, leading to arrestin binding to the
receptor for endosomal transport.
Arrestin facilitates protein transport, which prevents a receptor from reassociating with
the G protein complex.
Tasting involves many different cell-signaling processes that ultimately generate nerve
signals transduced by membrane depolarization. Sweet tastes result in PIP2 hydrolysis,
while salty tastes allow sodium ions to directly alter the membrane potential. What can
you deduce about the signaling mechanisms for sweet and salty? - ANSWERSodium
ions directly enter the cells, indicating the signal is transduced by an ion channel.
Sweet utilizes the GPCR signaling pathway, activating phospholipase C.
You have a mystery hormone (agonist), and to test the nature of the agonist you add it
to a dish of cultured liver cells. Shortly afterward you observe an increase in protein
kinase activity. In a second experiment, you find the kinase is inhibited if you add an
adenylate cyclase inhibitor to the cells prior to adding your mystery agonist. Which kind
of receptor system is the agonist signaling through? - ANSWERGPCR
Glucagon binding to the glucagon receptor inhibits which of the following processes? -
ANSWERGlycogen synthesis
While glucagon (a peptide) and epinephrine (a tyrosine derivative) are very different
agonists, both signal through GPCR systems. Some of the components of the pathways
are unique, while other signaling components are shared between both systems. Place
each item in the appropriate category: glucagon and epinephrine shared, glucagon
independent, or epinephrine independent.
Shared:
Glucagon Independent:
Epinephrine Independent: - ANSWERShared:
Net accumulation of glucose
Adenylate cyclase activation
Gsa activation
cAMP signaling pathways
, Glucagon:
Peptide binding to GPCR receptor
Epinephrine:
Ligand binding to adrenergic receptor
Activation of phospholipase C
Gqa activation
When ATCase is in the __________ state it indicates that ____________ is bound, and
that ATCase is ______________ regulated. - ANSWERT; CTP; down
Consider the reaction shown below
(A) Identify the kind of chemical catalysis
(B) Identify which of the amino acids can act as X in the reaction
Choose ONE correct answer for each (A and B). - ANSWERAcid-Base catalysis
TYR
Which of the following are characteristics of allosteric enzymes such as aspartate
transcarbamoylase. There are only three correct answers. - ANSWEROften have a
sigmoidal (S-shaped) curve of Vo versus [S].
Undergo conformational changes between the R and T state.
Can have a regulatory subunit and catalytic subunit.
Signaling activity of G proteins is controlled by GTPase activating proteins (GAPs) and
Guanine exchange factors (GEFs). What are the mechanisms by which GAPs and
GEFs control G proteins (GPs)? - ANSWERGAPs inhibit GPs by stimulating GTP
hydrolysis; GEFs activate GPs by stimulating GDP-GTP exchange.
Acetylcholinesterase is an important enzyme in the nervous system.
Acetylcholinesterase activity is blocked by the nerve agent sarin gas, which forms a
covalent bond with a Ser in the active site of the enzyme. Sarin gas is a(n) -
ANSWERirreversible inhibitor
Which of the following are characteristics of allosteric enzymes like ATCase? Choose
the THREE that apply. Allosteric enzymes: - ANSWERtend to have a sigmoidal (S-
shaped) curve of V0 vs. [S].
interconvert between a more active form and less active form.
