If a metabolic enzyme __________ the energy of activation of a reaction, the rate of product
formation will __________.
decreases; increase
Vitamin C is required for prolyl hydroxylase to function. Prolyl hydroxylase enzyme activity
is necessary for the proper biosynthesis of collagen. Which of the following might result from
a deficiency in vitamin C?
a. higher risk of bone breakage
b. a red
higher risk of bone breakage
Which of the following is NOT a characteristic of an enzyme active site?
a. It has a three-dimensional shape.
b. It plays a role in increasing the energy of activation of the reaction being catalyzed.
c. It is a unique chemical environment.
d. It is where
It plays a role in increasing the energy of activation of the reaction being catalyzed.
A proposed structure of a bacterial membrane protein shows that the distance between
successive amino acids in a region crossing the membrane is 3.4 �. Recall that a typical lipid
bilayer is approximately 40 � across. Which of the following is the most li
The protein resembles a porin.
Which of the following statements is true for hemoglobin but NOT myoglobin?
a. The tertiary structure is made up of a globin fold.
b. The surface of its tertiary structure contains many hydrophobic amino acids.
c. It contains a proximal histidine that coo
The surface of its tertiary structure contains many hydrophobic amino acids.
In both myoglobin and hemoglobin, O2 reversibly binds to a(n) __________ atom contained
in a porphyrin ring that is tightly bound to the protein.
iron
Hemoglobin contains __________ ?-helices, __________ ?-sheets, and __________ globin
folds.
32; 0; 4
A reduction in the catalytic ability of carbonic anhydrase may lead to __________ efficient
oxygen delivery by hemoglobin as a result of a(n) __________ Bohr effect.
less; reduced
An effector binds to a single subunit of a multi-subunit allosteric protein. As a result, all
subunits switch to the R state. This is an example of the __________ model of allostery.
concerted
Which of the following is a positive effector for oxygen binding to hemoglobin?
a. CO2
b. O2
c. H+
d. 2,3-bisphosphoglycerate
O2
Nuclear receptors are a type of
cell signaling protein.
The estrogen receptor is a(n)
nuclear receptor.
Which of the following is NOT a transport protein?
a. maltoporin
b. hemoglobin
c. Na+ channel
d. DNA polymerase
DNA polymerase
Which of the following is a genomic caretaker protein?
a. topoisomerase
b. insulin
c. myoglobin
d. tubulin
topoisomerase
Which of the following directly requires ATP to carry out its function?
a. Cl? ion channel
b. malate dehydrogenase
c. myoglobin
d. protein kinase A
protein kinase A
When oxygen binds to hemoglobin, which of the following occurs?
a. The heme group becomes puckered.
b. The atomic radius of the iron is decreased.
c. His F7 is brought closer to the plane of the porphyrin ring.
d. His E8 is brought closer to the plane of
The atomic radius of the iron is decreased.
Consider the following interaction between a protein and its ligand: [P] + [L] ? [PL].
If [L] = 5 mM, [P] = 3 mM, and [PL] = 2 mM, what is the Ka for the interaction?
0.133 mM
Consider the following interaction between a protein and its ligand: [P] + [L] ? [PL].
If [L] = 5 mM, [P] = 3 mM, and [PL] = 2 mM, what is the dissociation constant?
7.5 mM
The estrogen receptor is an example of a
cell signaling protein
Which of the following groups are hydrogen bonded in oxyhemoglobin but not
deoxyhemoglobin?
a. Asp94 and Asn102
b. Asp94 and Tyr42
c. Try42 and Asp99
d. Asp99 and Asn102
Asp94 and Asn102
A mutation of the N-terminal valine in adult hemoglobin occurs. The amino acid is replaced
with an isoleucine. Studies show that the replacement does not alter the overall structure of the
protein. Which of the following hemoglobin functions may be altere
ability to transport CO2
The fractional saturation of hemoglobin (Hb) binding to oxygen is illustrated by
[HbO2] / ([HbO2] + [Hb]).
Oxygen binding is monitored for a solution of hemoglobin. During the experiment, the curve
changes from sigmoidal to hyperbolic. Which of the following may be the reason for the
change?
a. A positive allosteric effector was added.
b. A negative allosteric
The protein dissociated into individual subunits.
A protein that follows the concerted model of allosteric regulation would display a binding
curve that is __________. A protein that follows the sequential model of allosteric regulation
would display a binding curve that is __________.
sigmoidal; sigmoidal
Consider an allosteric protein that contains three identical subunits. Which of the following is
true only if the protein follows the concerted model of allostery and NOT the sequential
model of allostery?
a. All three subunits exist in the R state simult
A ligand is bound to a single subunit and that subunit is in the T state.
Which of the following pairs are paralogous genes?
a. chicken myoglobin; human hemoglobin ? subunit
b. chicken hemoglobin ? subunit; chicken hemoglobin ? subunit
c. human hemoglobin ? subunit; chicken hemoglobin ? subunit
d. chicken hemoglobin ? subunit;
chicken hemoglobin ? subunit; chicken hemoglobin ? subunit
The ? subunit of adult hemoglobin has higher sequence similarity to __________ than to
__________.
fetal ? subunit; myoglobin
Approximately how many amino acids are identical in both myoglobin and the adult ?-subunit
of hemoglobin?
20%
Which of the following is NOT a symptom of anemia?
a. fatigue
b. shortness of breath
c. cognitive decline
d. excessive bleeding
excessive bleeding
Which of the following is true of sickle cell anemia?
a. It is a dominant genetic disease.
b. It is caused by a mutation in the ?-globin gene.
c. It is caused by an amino acid substitution in the F helix.
d. It results in a hemoglobin that contains a hydr
It results in a hemoglobin that contains a hydrophobic amino acid on the surface.
Which of the following may result from a His143 ? Ala143 mutation in adult hemoglobin?
a. decreased CO2 transport efficiency
b. increased oxygen transport efficiency
c. reduced affinity for 2,3-BPG
d. sickle cell anemia
reduced affinity for 2,3-BPG
A molecule is found to be able to diffuse across a membrane. Which of the following
characteristics would best describe this molecule?
a. hydrophilic
b. hydrophobic
c. neutral
d. polar
hydrophobic
The translocation rate of a solute across a membrane is measured. A plot of translocation rate
versus solute concentration displays a hyperbolic curve. The translation
could be occurring through a passive transport carrier.
Consider a system where a passive transport channel is available for a neutral molecule X. If
RTln(C2/C1) is zero, then
no net transport will occur
Passive membrane transporters CANNOT
contain only hydrophobic amino acids
Gramicidin A is involved in the __________ transport of __________ charged ions.
passive; positively
Which of the following accounts for some of the specificity of the K+ channel?
a. The radius of solvated Na+ is smaller than the radius of solvated K+.
b. The number of ?-strands that make up the channel.
c. The orientation of backbone carbonyl oxygen ato
The orientation of backbone carbonyl oxygen atoms in the channel.
As K+ passes through the selectivity filter of the K+ channel of Streptomyces lividans it
interacts with
amino acid carbonyl groups.
In studying a transporter, it is found that no external energy input is needed to facilitate the
movement of a neutral compound through the transporter. The translocation rate of the
compound reaches a plateau at high levels of compound. It is a(n)
passive transport carrier
The selectivity of aquaporin for H2O relies on all EXCEPT which of the following?
a. hydrogen bonding to Asn
b. a 2.8 � constriction point within the protein
c. inverted ?-helix dipoles
d. electrostatic repulsion from Asn
electrostatic repulsion from Asn
Which is true of the K+ channel but NOT of an aquaporin?
a. Selectivity is achieved through interactions with backbone NH groups.
b. It contains ?-helices.
c. It is an active transporter.
d. Selectivity is assisted through inverted ?-helix dipoles.
Selectivity is achieved through interactions with backbone NH groups.
The E. coli maltoporin protein, but NOT the A. lividans K+ channel protein,
uses transport dependent on interaction with amino acid side chains.
Which of the following is a pharmaceutical drug that targets an active transporter?
a. sertraline
b. malate
c. gramicidin A
d. 2,3-BPG
sertraline
As 18 Na+ ions are exported out of the cell by the Na+-K+ ATPase membrane transport
protein, __________ K+ ions are imported into the cell.
12
A cell with a membrane potential of ?70 mV that contains functioning Na+-K+ ATPase
membrane transport proteins will maintain an extracellular __________ concentration that is
__________ than the intracellular __________ concentration.
K+; lower; K+
The mutation that would lead to the most dramatic effect on Ca2+ transport is a mutation of
Asp351 in SERCA.
Which of the following is NOT an ABC transporter?
a. cystic fibrosis transmembrane conductance regulator protein
b. SERCA
c. multidrug resistance protein
d. maltose transporter from E. coli
SERCA
Primary active ABC transporters and P-type transporters both require
a conformational change to function.
The lactose permease from E. coli and the molybdate transporter from Archaeoglobus
fulgidus both
undergo a conformational change that occurs on substrate binding.
What might be the effect on the transport of lactose into the cytosol of E. coli if a drug is
added that allows H+ to freely pass through the inner bacterial membrane?
Lactose transport would cease.
Which of the following is NOT considered part of the thin filament?
a. actin
b. myosin
c. troponin
d. tropomyosin
myosin
Titin functions to connect __________ to __________.
myosin proteins; Z-disk proteins
When ATP binds to myosin
it cannot interact with actin.
The sarcomere length of isolated heart myoblasts can be measured over time in the laboratory.
The myoblasts are maintained in a buffer during the experiment. In a control experiment, Ca2+
and ATP are added to the buffer and the change in sarcomere length
smaller
If SERCA is not functioning in a myoblast, which of the following may occur?
a. Myosin will not undergo the conformational change that results in the power stroke.
b. Myosin will not be able to bind to the thin filament.
c. The myofibrils can shorten but
The myofibrils can shorten but not lengthen.
After __________ induced changes in the structure of thin filament, myosin heads containing
__________ in the nucleotide binding site will bind with high affinity to actin subunits.
Ca2+; ADP + Pi
Consider the following interaction between a protein and its ligand: [P] + [L] ? [PL].
Which equation describes the dissociation constant of this interaction?
[P][L] / [PL]
An oxygen binding curve of fractional saturation versus pO2 displays a sigmoidal shape. This is
the oxygen binding curve for
hemoglobin in the presence of 2,3-BPG.
Consider an oxygen binding curve for hemoglobin at pH 7.4. The binding curve would shift
__________ if the pH is reduced to 7.2.
to the right
Which of the following would shift the oxygen binding curve for hemoglobin to the left?
a. a lower concentration of CO2
b. a higher pH
c. a higher concentration of 2,3-BPG
d. an increase in the number of hemoglobin molecules in the T state
a higher pH
Which of the following is NOT a definition of fractional saturation for a system of
[P] +[L] ? [PL]?
a. [PL] / [PL] + [P]
b. [PL] + [P] / [PL]
c. [L] / [L] + Kd
d. occupied binding sites / total binding sites
[PL] + [P] / [PL]
A protein displays allosteric regulation. Which of the following is true?
a. Each subunit is either in the T state or the R state, but does not switch from one state
to the other.
b. Each subunit can exist in more than one conformation.
c. When the protei
Each subunit can exist in more than one conformation.
A mutation in the ? subunit of hemoglobin is discovered that reduces the affinity of 2,3-BPG
binding. Which of the following mutations is most likely to have this consequence?
a. Val1 ? Ile1
b. Asp99 ? Glu99
c. Lys82 ? Asp82
d. Glu6 ? Val6
Lys82 ? Asp82
Passive transporter proteins allow molecules to move across a membrane in response to
chemical gradients
Which of the following is NOT a passive transporter protein?
a. porin
b. Cl? channel
c. Ca2+-ATPase transporter protein
d. Ca2+ channel
Ca2+-ATPase transporter protein
A myoblast contain(s) __________, but a myofibril does not.
many nuclei
Thin filaments __________, but thick filaments do/are not.
are directly attached to the Z disk
Fetal and adult hemoglobin have different affinities for 2,3-BPG. Predict if O2 transport from
maternal cells to fetal cells will be altered from the normal rate if the ? subunit of the fetal red
blood cells have a Ser143 ? His143 mutation. Include the te
When the fetal ? subunit contains Ser143 it has lower affinity for 2,3-BPG. 2,3-BPG binding
stabilizes the T state. If Ser143 is replaced by His143 the affinity for 2,3-BPG will be the same
as for adult hemoglobin, which contains His143. The affinities fo
A newly discovered transporter protein is being investigated using an assay to determine
whether transport has occurred in the cells. A nonhydrolyzable form of ATP is added to the
cells, and it is found that transport is reduced. Explain these results.
The transporter protein must be involved in active transport. When ATP is added but cannot
be hydrolyzed, the active transport protein is unable to function, leading to reduced transport.
An E. coli strain is discovered that has a mutation in the gene encoding RecBCD. The
mutation causes RecBCD to not function as effectively as the wild-type RecBCD. Hypothesize
how the growth rate of this strain would compare with that of the wild type.
RecBCD is a genomic caretaker protein. It functions to unwind the DNA double strand to allow
access for the binding of RecA, which mediates DNA repair and recombination. If RecBCD is
not functioning as efficiently, then DNA repair would also be less effic
Describe the two functional units of myoglobin that are responsible for O2 binding. Include the
type of chemical bond involved for each binding interaction (i.e., hydrogen bond, covalent
bond, electrostatic bond, etc.).
His E7 (distal histidine) binds to O2 through a hydrogen bond. The iron (Fe) of the heme group
binds to O2 by a covalent bond.
A new protein has been discovered that may be allosterically regulated. The protein is purified
and analyzed by SDS-PAGE followed by staining with Coomassie blue. A single band at 42 kDa
is seen on the gel. Explain how these data may or may not support th
These data do not support the belief that the protein is allosteric. Allosteric proteins must
have quaternary structure. SDS-PAGE disrupts quaternary structure. The fact that a single band
appeared on the gel does not indicate if the protein initially had
What is the clinical term for reduced O2 transport efficiency from the lungs to the tissues,
arising from altered hemoglobin function or reduced numbers of red blood cells per unit of
blood? Provide an example of a specific type of anemia that is caused b
Anemia; sickle cell anemia
An increase in sickle cell disease symptoms can occur when a person with the disease is at
higher altitudes. Hypothesize how allosteric regulation at high altitudes may be related to sickle
cell anemia.
At high altitudes, more 2,3-bisphosphoglycerate (2,3-BPG) is made. 2,3-BPA is a negative
allosteric effector of hemoglobin. It stabilizes the T state of hemoglobin. In the T state, HbS
polymer formation is higher than in the R state.
What role do ?S-Phe85 and ?S-Leu88 play in sickle cell anemia?
They interact with ?S-Val6 in another hemoglobin tetramer, which results in polymerization
of the hemoglobin.
What is required for the transport of a molecule by an active transporter that is not necessary
for a molecule to be transported by a passive transporter?
energy
The E. coli maltoporin protein is a homotrimeric porin complex. A related protein is found in
another bacterial species that does not form trimers but rather functions as a monomer. A
comparison of the amino acid composition of a maltoporin subunit and th
The porins are embedded in the membrane. For the trimer, the exterior of each subunit is
hydrophobic in the regions interacting with the membrane as well as the regions interacting
with the other subunits. For the monomer, the exterior is still hydrophobi
A passive transporter is discovered that can transport both galactose and glucose. The pore of
the transporter can accommodate a single sugar at a time. If the extracellular concentrations
of galactose and glucose are 0.2 and 3.6 mM, respectively, and the
Glucose is most likely to enter the cell through the transporter. First, it is at a higher overall
concentration and is more likely to randomly interact with the transporter. Second, the free
energy of transport for glucose is less than zero, whereas that
Explain how the five arginine residues found within the channel of Omp32 protein of the
bacterium Delftia acidovorans increase the specificity of the channel.
The arginine residues are negatively charged. They line the interior of the channel and
facilitate the movement of a positive molecule (malate) through the channel. They repel
negatively charged molecules that attempt to enter the channel.
There are two main structural differences between a typical ?-helix and the helix formed by
gramicidin A. Describe the two structural differences and choose which structural characteristic
is more important in the function of gramicidin A. Explain your ch
A typical ?-helix is left handed and has a tightly packed center. The helix of gramicidin A is
right handed and has a wider diameter leading to a channel within the helix. The width is more
important in the function of gramicidin A because it allows for t
Predict the effect on Na+ transport through gramicidin A if the helical structure took on the
conformation of a true ?-helix.
Na+ would no longer be transported because the helix would have a tightly packed center that
would not allow the ion to enter.
You design an experiment in which you can monitor the step-by-step movement of H+ and
Ca2+ through the SERCA protein, starting with the protein in the E2-ATP state and moving
through the transport cycle, ultimately returning to the E2-ATP state. Your cont
Only the E2-ATP conformation will be detected. The SERCA protein will bind the
non-hydrolyzable form of ATP but cannot hydrolyze it, a requirement for the release of H+
and binding of Ca2+ in the transmembrane helices.
Both SERCA and the Na+-K+ ATPase contain a P domain. Explain the general function of this
domain.
The P domain contains an amino acid that becomes phosphorylated. Phosphorylation leads to
activation of the protein through a conformational change.
Explain how a mutation in Asp351 of SERCA might alter Ca2+ transport.
Phosphorylation of Asp351 is required for SERCA to function as a Ca2+ transporter. If
Asp351 is mutated, SERCA would become inactive and Ca2+ transport would stop.
Propose how the addition of an inhibitor of the permeability glycoprotein transporter to a
chemotherapy drug regimen would alter the effectiveness of the regimen.
The permeability glycoprotein transporter, also known as the multidrug resistance protein,
functions to remove toxic compounds from a cell. Cancer cells can use this protein to export
chemotherapy drugs. Addition of an inhibitor would result in more of th
Complete the following bacterial ABC transporter protein process:
1. Binding of substrate carrier protein induces a conformational change to expose the substrate
binding site.
2. ATP hydrolysis causes a conformational change that releases substrate.
3.
Release of ADP + Pi and binding of ATP resets the transporter.
Explain why ABC transporters are channels and not carriers.
ABC transporters undergo large conformational changes, driven by the hydrolysis of ATP.
Radioactive iodine can be used in laboratory settings to label inhibitors. When working in a lab,
a researcher is exposed to the radioactive iodine when some accidentally spills on her exposed
wrist. A scan with a Geiger counter the next day indicates tha
Iodine is concentrated in the thyroid, which is located in the neck. The iodine is brought in
through the Na+-I? symporter. This is a secondary transporter that relies on the Na+ gradient
that is established by the Na+-K+ ATPase primary active transporter
Articulate the difference between a myoblast and a myofibril.
A myoblast is a large fused cell that contains many nuclei and shares a common plasma
membrane (sarcolemma). Myofibrils are found inside myoblasts and bundles of fibers made up
primarily of myosin and actin.
Construct a complete actin-myosin reaction cycle by placing the following steps in order,
starting with Ca2+ binding to troponin:
A. ADP release empties the nucleotide binding site in myosin.
B. Pi release induces the power stroke.
C. ATP hydrolysis induc
B, A, D, C
Explain the relationship between P50 of oxygen binding and Kd for oxygen binding to
myoglobin.
P50 is the amount of oxygen bound when half of the oxygen binding sites are saturated. It is
the partial pressure of oxygen that results in a fractional saturation value of 0.5. In any
ligand-binding system, the concentration of ligand required to reach a
In the shift from the T to the R state in adult hemoglobin, a shift between the subunits occurs.
Explain how this shift leads to the variation of binding affinity for 2,3-BPG in the two states.
The shift from the T state to the R state makes the central cavity between the four subunits
smaller. 2,3-BPG cannot bind as well to the smaller cavity, which is why there is a lower
affinity for 2,3-BPG when the hemoglobin subunits are in the R state.