Biochem Quiz 7

In sickle-cell anemia, the gene coding for the beta-chain of hemoglobin shows- Select one: a. A nonsense mutation leading to the formation of a shortened polypeptide b. A missense mutation leading to elimination of the heme prosthetic group, where oxygen binds c. A missense mutation leading to a substitution of Glu to Val d. A missense mutation leading to the elimination of the central cavity in hemoglobin

a. A nonsense mutation leading to the formation of a shortened polypeptide

The initial trigger for conformational change in hemoglobin, leading to the T/R transition, involves: Select one: a. Shift in the porphyrins plane upon oxygen binding, from concave to planar b. Shift in the relative position of the alpha and beta subunits c. Dramatic change in the affinity to oxygen in all four binding sites d. Increase in the blood's BPG concentration

a. Shift in the porphyrins plane upon oxygen binding, from concave to planar

Which of the following is the major form of hemoglobin produced in red blood cells during normal adult life? Select one: a. alpha2/beta2 b. alpha2/gamma2 c. zeta2/epsilon2 d. alpha2/delta2 e. alpha2/epsilon2 Feedback

a. alpha2/beta2

In the binding of oxygen to myoglobin, the relationship between the concentration of oxygen and the fraction of binding sites occupied can best be described as: Select one: a. hyperbolic. b. sigmoidal. c. linear with a positive slope. d. linear with a negative slope. e. random.

a. hyperbolic.

Which expression is the fraction of oxygen-bound myoglobin in solution (theta, or Y)? Select one: a. pO2/pO2 + p50 b. [Mb][O2]/[MbO2] c. [Mb]+ [MbO2] d. [MbO2]/[Mb][O2]

a. pO2/pO2 + p50

The graph below illustrates that: (SEE QUESTION 27 QUIZ 7) Select one: a. As the curve shifts to the right, the affinity of hemoglobin to oxygen increases b. As the curve shifts to the right, the affinity of hemoglobin to oxygen decreases c. That saturation curves cannot be a reliable measure of affinity of hemoglobin to oxygen d. Scientists still do not know for sure which binding curve works in the physiological state

b. As the curve shifts to the right, the affinity of hemoglobin to oxygen decreases

The hypothesis that hemoglobin shifts between a low and a high affinity form implies that the protein- Select one: a. Has a prosthetic group b. Exists in two distinct conformations c. Has two binding sites for oxygen d. Is coded by two different genes e. All of the above

b. Exists in two distinct conformations

Which of the answers is INCORRECT regarding the following molecule: SEE QUESTION 30 QUIZ 7 Select one: a. It binds better in adult hemoglobin than in fetal hemoglobin b. It binds both myoglobin and hemoglobin c. It has a role in modulating the binding of oxygen d. Red blood cells have it

b. It binds both myoglobin and hemoglobin

Le Chatelier principle predicts that: Select one: a. Oxygen will dissociate from hemoglobin where blood oxygen is high b. Oxygen will dissociate from hemoglobin where blood oxygen is low c. Oxygen will bind hemoglobin where blood oxygen is low d. Oxygen will only bind hemoglobin in the R state e. Oxygen will only dissociate from hemoglobin in the T state

b. Oxygen will dissociate from hemoglobin where blood oxygen is low

BPG binding to hemoglobin requires that: Select one: a. The protein will be in the R state b. The protein will be in the T state c. The protein will have all its four heme groups bound to oxygen d. The protein will have oxygen dissociated from all its four heme groups e. The red blood cells will be as close as possible to the lungs

b. The protein will be in the T state

In the concerted model for cooperativity, the hemoglobins subunits- Select one: a. bind or release oxygen, all at once b. change T to R or vice versa, all at once c. bind oxygen in order, first the two alpha subunits, then the two beta subunits d. show maximum cooperativity when no BPG is present

b. change T to R or vice versa, all at once

When the dissociation constant (Kd) of any ligand is smaller by comparison, it means- Select one: a. the ligand binds with lower affinity b. the ligand binds with higher affinity c. the concentration of the ligand has decreased d. the concentration of the ligand has increased

b. the ligand binds with higher affinity

In a fetus, Hemoglobin has gamma chains instead of beta chains. One difference is less positive charges in the central cavity of Hemoglobin. This increases the affinity of Hemoglobin to oxygen because: Select one: a. It creates less electrostatic repulsion between the subunits of Hemoglobin b. It allows BPG to bind more tightly c. BPG binds less tightly d. It prevents the T/R transition.

c. BPG binds less tightly

Which of the following is NOT correct concerning 2,3-bisphosphoglycerate (BPG)? Select one: a. It binds at a distance from the heme groups of hemoglobin. b. It binds with lower affinity to fetal hemoglobin than to adult hemoglobin. c. It increases the affinity of hemoglobin for oxygen. d. It is an allosteric modulator. e. It is normally found associated with the hemoglobin extracted from red blood cells.

c. It increases the affinity of hemoglobin for oxygen.

When moving towards the lungs, hemoglobin shifts to the ____________ conformation, in which the Kd for oxygen binding is _________. Select one: a. R;increased b. T; lowered c. R; lowered d. T; increased

c. R; lowered

The following illustration shows: (SEE QUIZ 7 QUESTION 3) Select one: a. The spontaneous conversion of CO to O2 on the heme site, in the presence of E7 b. That histidine E7 is not always needed c. That in the presence of E7, the binding configuration of CO to heme changes d. That in the presence of E7, CO and O2 are configured at the binding site the same way, but O2 binds with higher affinity e. A and B are correct f. C and D are correct

c. That in the presence of E7, the binding configuration of CO to heme changes

We are protected to some extent against low level CO poisoning because: Select one: a. His F8 on hemoglobin distorts the heme iron atom out of the heme plane and attracts O2, but not CO. b. Affinity of heme for O2 is much greater than for CO c. The binding configuration of CO to heme iron favors oxygen binding d. CO cannot bind to heme in hemoglobin e. All of the above

c. The binding configuration of CO to heme iron favors oxygen binding

Myoglobin and Hemoglobin share the following properties EXCEPT: Select one: a. They both have a heme prosthetic group that binds oxygen b. They are both oxygen carrier proteins c. They are both located in the blood's red cells d. Their polypeptide structures are mainly alpha helices e. They share a common evolutionary linkage

c. They are both located in the blood's red cells

The experimental proof for distinct T and R hemoglobin came from- Select one: a. Oxygen binding experiments b. Determination of molecular weight of hemoglobin subunits c. X-ray diffraction studies d. Sequencing of the genes coding for hemoglobin's subunits e. Experiments with carbon monoxide

c. X-ray diffraction studies

In myoglobin's binding curve, the dissociation constant (Kd) is- Select one: a. [Mb]+ [MbO2] b. pO2/pO2 + p50 c. [Mb][O2]/[MbO2] d. The [oxygen] that gives half maximal binding

c. [Mb][O2]/[MbO2]

The interactions of ligands with proteins: Select one: a. are relatively non-specific. b. are usually irreversible. c. are usually short-lived d. usually result in the inactivation of the proteins. e. are relatively rare in biological systems.

c. are usually short-lived

The Hills coefficient- Select one: a. represent the total number of ligand binding sites in the protein b. is greater for myoglobin than it is for hemoglobin c. is larger when cooperativity is larger d. is the difference (delta) in fraction bound (theta, or Y) to hemoglobin between the lungs and capillaries

c. is larger when cooperativity is larger

When O2 binds to heme in hemoglobin, the _____ is drawn into the plane of the porphyrin, causing a conformational change that is transmitted to adjacent subunits, ________ the affinity for additional O2 binding. Select one: a. Histidine E7; lowering b. Fe+2 atom; lowering c. BPG; increasing d. Fe+2 atom; increasing e. Histidine E7; increasing

d. Fe+2 atom; increasing

When red blood cells migrate away from the lungs, initial oxygen dissociation from hemoglobin is stimulated by __________ and further on, dissociation is enhanced by _________: Select one: a. BPG; breathing b. Higher [oxygen]; Lower [oxygen] c. BPG; T/R transition d. Lower [oxygen]; T/R transition

d. Lower [oxygen]; T/R transition

Which of the following properties is SHARED by both myoglobin and Hemoglobin? Select one: a. If have a point mutation from Glu to Val, they both have the ability to cause sickle-cell anemia b. They are both alllosteric proteins c. They both bind BPG d. They will both bind more O2 where it is more abundant, release O2 where it is more scarce e. The amino acid sequence of any of the hermoglobin's subunits is identical with that of the myglobin sequence

d. They will both bind more O2 where it is more abundant, release O2 where it is more scarce

The binding of one or more O2 ligands to a molecule of hemoglobin will induce: Select one: a. the release of any other O2 that may have bound earlier. b. a decrease in hemoglobin's ability to bind a second O2. c. dissociation of the hemoglobin subunits. d. the movement of hemoglobin to an organism's muscle tissue. e. an increased affinity for O2 in the remaining subunits (which have not yet bound O2).

e. an increased affinity for O2 in the remaining subunits (which have not yet bound O2).

A prosthetic group of a protein is a non-protein structure that is: Select one: a. a part of the secondary structure of the protein. b. a substrate of the protein. c. a ligand of the protein. d. transiently bound to the protein. e. permanently associated with the protein

e. permanently associated with the protein

The following illustration demonstrates: SEE QUESTION 28 QUIZ 7 Select one: a. That Heme exists in two possible configurations b. That oxygen binding locks heme in one specific configuration c. That the configuration of Helix F is affected by the configuration of the heme group d. That O2 binding always results in a T to R conversion e. A, and B are correct f. A, B and C are correct g. A, B, C, and D are correct

f. A, B and C are correct

The physiological increase in the blood level of BPG is an adaptation to higher elevation because Select one: a. More hemoglobin will stay in the R state b. BPG increases the affinity of hemoglobin to O2 c. Hemoglobin has a reduced capacity to carry O2 in the capillaries d. Hemoglobin's ability to bind O2 near the lungs remains virtually unchanged e. A and B f. C and D

f. C and D

The following graph shows that: SEE QUESTION 29 QUIZ 7 Select one: a. BPG always increases the binding of oxygen to hemoglobin b. BPG always decreases the binding of oxygen to hemoglobin c. BPG always increases delivery of O2 to the tissues d. BPG always decreases delivery of O2 to the tissues e. A and C are correct f. B and D are correct g. B and C are correct h. A and D are correct

g. B and C are correct