Deck 19: Allosterism and Receptor-Ligand

Question 1

Allosterism

A) means "other shape"
B) is induced by binding of another molecule to a protein
C) is important to protein regulation
D) leads to change in conformation and activity
E) All of the above

Answer 1

All of the above

Question 2

What is the difference between allosteric and orthosteric regulation?

A) All enzymes are regulated orthosterically only.
B) All enzymes are regulated allosterically only.
C) Only in allosteric regulation of an enzyme does the substrate bind to the active site
D) In allosteric regulation of an enzyme, the substrate binds to the allosteric site
E) In allosteric regulation of an enzyme, a molecule other than the substrate binds a site other than the active site

Answer 2

In allosteric regulation of an enzyme, a molecule other than the substrate binds a site other than the active site

Question 3

Proteins/enzymes that can be regulated allosterically
I. show a hyperbolic Michaelis-Menten curve
II. can be regulated by molecules that differ structurally from a substrate
III. can be both activated and inhibited
IV. undergo only competitive inhibition

A) I and II
B) II and III
C) I, II and III
D) I, III and IV
E) I, II, III and IV

Answer 3

II and III

Question 4

Proteins such as hemoglobin are known as ________ proteins since binding of a molecule to one site alter binding to other sites.

A) ligand-activated
B) allosteric
C) induced-fit
D) catalytic
E) none of the above

Question 5

Hemoglobin's subunits bind oxygen in a ______ manner.

Question 6

Models of allosterism describe the conformational change between the tense (T; low affinity) and the relaxed (R; high affinity) states of protein structure. These include a concerted model, in which subunits of proteins transition between T and R states one at a time, and a sequential model, where all subunits transition between the T and R states at the same time, as regulators bind.

A) Both sentences are true
B) Both sentences are false
C) The first sentence is true and the second sentence is false
D) The first sentence is false and the second sentence is true

Question 7

In the sequential model of allosterism, as regulatory molecules bind to allosteric sites,

A) the active site-containing subunit shifts from T to R state
B) the active site-containing subunit is activated
C) the entire complex exists in the T or R state
D) subunits in the T state have high affinity
E) Both A and B

Question 8

Enzymes that are allosterically regulated

A) show an activity vs. substrate concentration curve that is sigmoidal
B) may be stimulated by allosteric activators
C) when inhibited show an activity curve shifted to the right
D) Both A and B
E) All of the above

Question 9

Heterotropic regulation
I. occurs with a molecule other than the protein's substrate
II. occurs with regulator binding at a site other than the active site
III. influences substrate binding
IV. is a type of competitive inhibition

A) I and II
B) II and III
C) II, III and IV
D) I, III and IV
E) I, II and III

Question 10

As associated with hemoglobin, heme is considered a _____.

A) catalyst
B) subunit
C) coenzyme
D) cofactor
E) none of the above

Question 11

In its reduced form, the central ion of the heme group of hemoglobin is _____.

A) Cu⁺
B) Cu²⁺
C) Fe²⁺
D) Fe³⁺
E) none of the above

Question 12

Myoglobin is _____; hemoglobin is _____.

A) monomeric; dimeric
B) monomeric; trimeric
C) monomeric; tetrameric
D) dimeric; trimeric
E) dimeric; tetrameric

Question 13

The individual hemoglobin subunits and myoglobin share similar _____ structure but have rather different _____ structure.

A) primary; secondary
B) secondary; tertiary
C) primary; tertiary
D) secondary and tertiary; primary
E) primary and secondary; tertiary

Question 14

In the ______ state of hemoglobin, the iron ion is out of the plane of the porphyrin ring.

Question 15

A plot of the binding of oxygen to myoglobin as a function of pO2 gives a _____ shape; a similar plot for hemoglobin gives a _____ shape.

A) sigmoidal; sigmoidal
B) sigmoidal; hyperbolic
C) hyperbolic; sigmoidal
D) hyperbolic; hyperbolic
E) hyperbolic; exponential

Question 16

The idea that binding of one molecule of oxygen to hemoglobin enhances further binding of oxygen to hemoglobin is called _____.

A) homologous binding
B) cooperativity
C) fractional saturation
D) allosterism
E) none of the above

Question 17

With respect to oxygen saturation, hemoglobin is _____ saturated at the pO₂ of the lungs and _____ saturated at the pO₂ of the tissue

A) 20%; 20%
B) 25%; 20%
C) 50%; 20%
D) 50%; between 30 and 70%
E) >90%; 10-30%

Question 18

While the composition of hemoglobin in adult humans is $\alpha$ ₂ $\beta$ ₂, in the developing fetus, _____ is observed

A) ₂ $\varepsilon$ ₂
B) $\alpha$ ₂11ef2e2b_b93d_a1be_a6da_ad5312849ad2_TB9579_11₂
C) $\alpha$ ₂ $\varepsilon$ ₂
D) $\alpha$ ₂ $\delta$ ₂
E) $\alpha$ ₂ $\gamma$ ₂

Question 19

The graph to the right, where YO2 represents %O2 saturation, will be used for the following questions

-Plot ___ is ___ and represents ___

A) A; hyperbolic; myoglobin
B) B; sigmoidal; hemoglobin
C) B; hyperbolic; hemoglobin
D) A; sigmoidal; hemoglobin
E) Both A and B

Question 20

The graph to the right, where YO2 represents %O2 saturation, will be used for the following questions

-Point C on the graph above

A) represents the situation in the lung, where oxygen is abundant
B) oxygen is bound tightly to hemoglobin
C) represents the situation in the tissues, where oxygen is abundant
D) represents the situation in the tissues, where oxygen is deficient
E) hemoglobin is saturated with oxygen

Question 21

The graph to the right, where YO2 represents %O2 saturation, will be used for the following questions
-The sigmoidal nature of the plot of oxygen binding to hemoglobin indicates ___ among hemoglobin's subunits.

Question 22

The graph to the right, where YO2 represents %O2 saturation, will be used for the following questions

-The plot above describes the Bohr effect. If a third plot were added, a sigmoidal one between plots A and B,

A) this third plot would suggest an increased affinity of oxygen for hemoglobin
B) it would represent adult hemoglobin, and plot B would represent fetal hemoglobin
C) it would likely be seen if hemoglobin were in a more acidic environment
D) it would represent fetal myoglobin, and plot A would represent adult myoglobin
E) it would represent fetal hemoglobin retained in the T state

Question 23

The structure of the globin protein plays an important role in the affinity of hemoglobin for oxygen.

A) Key his and arg residues on the - subunits play a role in conversion of high affinity T to low affinity R states
B) Key his and asp residues on the - subunits play a role in conversion of low affinity T to high affinity T states
C) Key his and asp residues on the- subunits play a role in conversion of low affinity T to high affinity R states
D) Key his and asp residues on the - subunits play a role in conversion of high affinity T to low affinity R states
E) None of the above is correct

Question 24

At active muscle
I. pCO2 is high
II. acidity is low
III. carbamate forms
IV. hemoglobin is stabilized in the T state

A) I only
B) I and III
C) II, III and IV
D) I, III and IV
E) I, II, III and IV

Question 25

At high pCO2, the oxygen binding curve of hemoglobin, demonstrating the Bohr effect

A) takes on a hyperbolic shape
B) shifts to the right
C) shifts to the left
D) Both A and B are correct
E) None of the above

Question 26

The absence of 2,3-bPG causes hemoglobin's affinity for oxygen to______.

Question 27

Which allosteric effector has the greatest ability to stabilize the deoxy state of hemoglobin?

A) bPG
B) CO₂
C) O₂
D) H⁺
E) all of the above have equal ability

Question 28

Which gas does NOT bind to the heme Fe+2 ion in myoglobin?

A) NO
B) CO
C) HCO3-
D) O₂
E) H₂S

Question 29

Cl- ion plays a role in the transport of CO2 in plasma

A) It exchanges for HCO3- through an antiport in the erythrocyte membrane
B) It maintains the ionic homeostasis of erythrocytes
C) It enters the erythrocyte at the lung in exchange for an HCO3- molecule
D) It serves as a cofactor for carbonic anhydrase, which is necessary for CO2 to be converted to HCO3-
E) Both A and B are correct

Question 30

Which of the following best explains the ability for carbon monoxide (CO) to bind to hemoglobin (HB. despite the relatively low concentrations of CO?

A) CO binds to Hb with less affinity than oxygen
B) CO binds to Hb with an affinity about the same as oxygen
C) CO binds to Hb about 5 times more strongly than oxygen
D) CO binds to Hb about 250 times more strongly than oxygen
E) none of the above

Question 31

How does CO₂ affect hemoglobin-oxygen binding?

A) CO₂ binds directly to the oxygen binding site, displacing oxygen and thus promoting the deoxy state
B) CO₂ displaces BPG, thus promoting the oxy state
C) CO₂ is converted to bicarbonate and H⁺ which promotes the oxy state
D) CO₂ is converted to bicarbonate and H⁺ which promotes the deoxy state
E) none of the above

Question 32

In hemoglobin of sickle cell anemia patients, a ___ residue is replaced by a ___ residue.

Question 33

In hemoglobin of sickle cell anemia patients, a valine residue binds to a(n) ___ patch causing ___ of the hemoglobin.

Question 34

The aggregation of hemoglobin of sickle cell anemia patients occurs in the ___ state, thus the formation of aggregates is most likely to occur in the ___.

Question 35

Sickle cell hemoglobin does not form fibers in the ______ form.

Question 36

Thalassemia is most often caused by an error in

A) mitochondrial DNA
B) homologous crossover
C) meiosis
D) mRNA splicing
E) translation

Question 37

Which is NOT true of nuclear receptors?

A) Those found in the cytosol translocate to the nucleus
B) They may never leave the nucleus
C) They bind hydrophilic signal molecules
D) They bind specific sites on DNA, altering gene expression
E) They act as transcription factors

Question 38

Coactivators

A) bind at the ligand-binding domain of nuclear receptors
B) bind when the receptor is not yet bound to the hormone
C) bind in the cytosol when the hormone-receptor complexes forms
D) repress gene transcription
E) must be present for the receptor-ligand complex to bind the HRE

Question 39

Most nuclear receptor proteins include

A) a zinc-finger motif
B) a ligand binding domain with a hydrophobic cleft
C) cys and his residues that can chelate Zn ion
D) All of the above

Question 40

Ligands bind membrane bound receptors via

A) hydrogen bonds
B) hydrophobic interactions
C) disulfide bonds
D) Both A and B
E) All of the above

Question 41

The structure of membrane bound receptors includes

A) an intracellular ligand-binding domain
B) an extracellular domain that serves to induce intracellular changes
C) a catalytically-active site
D) None of the above

Question 42

The acetylcholine receptor is an example of a(n)

A) nuclear receptor
B) ion channel-linked receptor
C) 7-transmembrane helix (7TM) type receptor
D) tyrosine kinase receptor
E) enzyme-linked receptor

Question 43

In general, ion channel-linked receptors are important to binding hormones such as insulin and steroids. Many common ion channel-linked receptors are cys-loop receptors, which have five subunit, and a total of about 20 helices important to spanning the lipid bilayer and interacting with ligands.

A) Both sentences are true
B) Both sentences are false
C) The first sentence is true and the second sentence is false
D) The first sentence is false and the second sentence is true

Question 44

Many ion channel-linked receptors which respond to neurotransmitters such as acetylcholine and GABA allow passage of

A) Na+ to afford an action potential or muscle contraction
B) Ca+2 to afford muscle contraction
C) Na+ to stimulate metabolic processes
D) Zn+ to stimulate inflammatory response
E) Fe+2 to encourage oxygen binding

Question 45

G protein-coupled receptors

A) also serve as transcription factors
B) generally reside in the cytosol
C) also have catalytic ability
D) work through cellular second messengers
E) bind hydrophobic hormones such as steroids

Question 46

Which is NOT true of enzyme-linked receptors?

A) The insulin receptor is an example of an enzyme-linked receptor
B) Unlike nuclear receptors, enzyme-linked receptors do not need to dimerize for activity
C) Following ligand binding, enzyme-linked receptors undergo autophosphorylation
D) The enzyme-linked receptors themselves phosphorylate other intracellular proteins

Question 47

Molecules that act identically like a receptor's natural ligand
I. are termed agonists
II. may compete with the natural ligand for the receptor binding site
III. as inverse agonists activate the receptor to a lesser extent
IV. as partial agonists can cause a different cellular effect than the natural
Ligand

A) I and II
B) III and IV
C) I and III
D) I, III and IV
E) II, III and IV

Question 48

An antagonist and an inverse agonist are similar in that

A) both bind the receptor ligand-binding site
B) with both, the cellular effect is similar to the absence of natural ligand
C) with both, the receptor is irreversibly blocked
D) both lower the ability of the natural ligand to bind due to conformational changes to the receptor
E) None of the above is correct

Question 49

A plot of ligand concentration vs receptor sites bound (a Scatchard plot)

A) would likely be hyperbolic in nature for enzyme-linked receptors, because these have only one binding site and no subunits
B) would likely be sigmoidal in nature for enzyme-linked receptors, because these have only one binding site and no subunits
C) would likely be hyperbolic in nature for ion channel-linked receptors because they have several subunits that can be affected by sequential binding
D) would likely be hyperbolic in nature for G protein-linked receptors because they have several subunits that can be affected by sequential binding
E) would likely be hyperbolic in nature for G protein-linked receptors because they have several subunits that can be affected by concerted binding