Question 1

When O₂ binds,which of the following components of the heme group is drawn into the plane of the porphyrin,causing a conformational change that is transmitted to adjacent subunits,enhancing the affinity for additional O₂ binding?
A)Mg
B)CO
C)His
D)Fe

Accepted Answer

When O₂ binds, the iron (Fe) component of the heme group is drawn into the plane of the porphyrin, causing a conformational change that is transmitted to adjacent subunits, enhancing the affinity for additional O₂ binding.

Question 2

Which of the following conditions causes cell sickling in sickle cell anemia?
A)interaction of oxyHb S with the cell membrane
B)precipitation of deoxyHb S into long,chain-like fibres
C)formation of oxyHb S complexes and subsequent cell disruption
D)precipitation of Hb S-Hb A hybrid molecules

Accepted Answer

Sickling in sickle cell anemia occurs due to the precipitation of deoxyHb S into long chain-like fibres, which distort the shape of red blood cells and cause them to become sickle-shaped.

Question 3

Which of the following components of the eukaryotic PDH complex has the largest number of subunits? A)lipoate B)E₂ C)TPP D)E₃

Accepted Answer

The answer of Which of the following components of the...

Question 4

Why does fetal hemoglobin (Hb F)have an intrinsically greater affinity for O₂ than adult hemoglobin (Hb A)?
A)Hb F has a diminished capacity to bind BPG compared to Hb A.
B)Hb A has more subunits than does Hb F.
C)BPG binds Hb F with greater affinity than it binds Hb A.
D)The pH of fetal blood is lower than the pH of maternal blood.

Accepted Answer

Hb F has a lower affinity for 2,3-bisphosphoglycerate (BPG) than Hb A, which allows it to bind oxygen more tightly. BPG is a molecule that stabilizes the deoxygenated form of hemoglobin, decreasing its affinity for oxygen. Since Hb F binds less BPG, it can more readily pick up oxygen from maternal blood.

Question 5

The PDH complex is allosterically activated and inhibited by multiple modes.Which of the following is a correct relation?
A)acetyl-CoA: activation
B)NAD⁺: inhibition
C)NADH: activation
D)CoA-SH: activation

Accepted Answer

CoA-SH (coenzyme A) allosterically activates the pyruvate dehydrogenase (PDH) complex by promoting the removal of acetyl groups from the enzyme, thereby enhancing its activity.

Question 6

Which of the following is NOT a difference between the T form (tense or taut form)of deoxyhemoglobin and the oxyhemoglobin (the R form or relaxed form)?
A)covalent linkages between subunits
B)specific intrachain hydrogen bonds
C)salt links (ion-pair bonds)between ?-subunits
D)interchain salt bridges

Accepted Answer

Covalent linkages between subunits are the same in both T and R forms of hemoglobin. The differences lie in specific intrachain hydrogen bonds, salt links between b-subunits, and interchain salt bridges.

Question 7

Which of the following is a function of the polypeptide of myoglobin?
A)protects the heme iron from oxygenation
B)keeps the heme iron in the ferric form
C)provides a pocket for iron to fit
D)cradles the heme group

Accepted Answer

The polypeptide of myoglobin cradles the heme group, which is the site where oxygen binds. The heme group consists of an iron atom, and the polypeptide provides a specific pocket for the iron to fit. This interaction allows myoglobin to bind and release oxygen selectively. Therefore, choice D is the correct function of the polypeptide of myoglobin.

Question 8

Which of the following is NOT a characteristic of hemoglobin's binding of oxygen?
A)CO₂ promotes dissociation of O₂ from hemoglobin by lowering the pH.
B)Protons promote binding of oxygen by Hb.
C)2,3-Bisphosphoglycerate (BPG)promotes release of O₂ by Hb.
D)CO₂ can bind with Hb's free amino groups and stabilize deoxyHb.

Accepted Answer

Protons actually promote release of O₂ by Hb, not binding. This is known as the Bohr effect.

Question 9

Which of the following is the reason why BPG shifts the oxygen saturation curve of Hb to the right?
A)BPG binds to deoxyHb and unloads O₂ at tissues.
B)BPG binds to oxyHb and unloads O₂ at tissues.
C)BPG binds to deoxyHb and unloads O₂ at the lungs.
D)BPG binds to oxyHb and unloads O₂ at the lungs.

Accepted Answer

BPG binds to deoxyhemoglobin (deoxyHb), which stabilizes the T (tense) state of hemoglobin, making it easier for oxygen to be unloaded at tissues where it is needed.

Question 10

Which of the following mechanisms explains how carbon dioxide affects O₂ binding to Hb?
A)by directly binding to heme-Fe in the oxygen binding site
B)by forming iron carbonate with the heme-iron
C)by forming HCO₃-,which combines with H⁺ to increase CO₂ binding
D)by forming H⁺ + HCO₃-,where the H⁺ is an antagonist to oxygen binding to Hb

Accepted Answer

Carbon dioxide forms carbonic acid (H₂CO₃) in the blood, which dissociates into bicarbonate (HCO₃-) and hydrogen ions (H⁺). The increase in H⁺ concentration lowers the blood pH, which in turn affects the oxygen-binding affinity of hemoglobin (Hb) through the Bohr effect. The Bohr effect describes how a decrease in pH (increase in H⁺ concentration) reduces hemoglobin's affinity for oxygen, facilitating oxygen release to tissues. This mechanism does not involve CO₂ directly binding to the heme-iron or forming iron carbonate; instead, it operates through the changes in pH mediated by the products of CO₂ hydration.

Question 11

Which of the following regarding the effect of protons on binding of O₂ by hemoglobin is NOT correct?
A)The saturation curve of Hb for O₂ is displaced to the left (greater binding)as acidity increases.
B)Actively metabolizing tissues produce acid,which is an antagonist of oxygen binding by Hb.
C)As pH decreases,dissociation of O₂ from Hb is enhanced.
D)The phenomenon is called the Bohr effect.

Accepted Answer

The saturation curve of Hb for O₂ is actually displaced to the right (lesser binding) as acidity increases, not to the left. This reflects decreased affinity of hemoglobin for O₂ at lower pH levels.

Question 12

Which of the following regarding the differences between Hb and Mb is NOT correct?
A)Hb shows sigmoidal,whereas Mb shows hyperbolic oxygen saturation curves.
B)Hb shows cooperativity,whereas Mb does not.
C)Hb binds O₂ more tightly than Mb.
D)Hb-oxygen binding is dependent on physiological changes in pH,whereas Mb-oxygen binding is not.

Accepted Answer

This statement is not correct. Mb binds O₂ more tightly than Hb. Hb is designed to pick up O₂ in the lungs, where the partial pressure of O₂ is high, and release it in the tissues, where the partial pressure of O₂ is lower. Mb, on the other hand, is found in the muscles and has a higher affinity for O₂, which allows it to hold onto O₂ and deliver it to the mitochondria for use in oxidative phosphorylation.

Question 13

Why are we are protected to some extent against low level CO poisoning?
A)His F8 on Hb distorts the heme iron atom out of the heme plane and attracts O₂,but not CO.
B)Affinity of Hb for O₂ is much greater than for CO.
C)His E7 blocks perpendicular binding of CO to heme iron,allowing for better binding competition by O₂.
D)The competition of O₂ for heme is much greater than CO for heme.

Accepted Answer

His E7 (histidine at the E7 position) in hemoglobin plays a role in blocking the perpendicular binding of carbon monoxide (CO) to the heme iron, which allows oxygen (O₂) to compete more effectively for binding sites on hemoglobin. This structural feature helps in protecting against low-level CO poisoning by reducing the affinity of hemoglobin for CO compared to O₂, thus allowing oxygen to be more effectively transported in the presence of CO.

Quiz 14: Enzyme Regulation

When O₂ binds,which of the following components of the heme group is drawn into the plane of the porphyrin,causing a conformational change that is transmitted to adjacent subunits,enhancing the affinity for additional O₂ binding?

Which of the following conditions causes cell sickling in sickle cell anemia?

Which of the following components of the eukaryotic PDH complex has the largest number of subunits?

Why does fetal hemoglobin (Hb F) have an intrinsically greater affinity for O₂ than adult hemoglobin (Hb A) ?

The PDH complex is allosterically activated and inhibited by multiple modes.Which of the following is a correct relation?

Which of the following is NOT a difference between the T form (tense or taut form) of deoxyhemoglobin and the oxyhemoglobin (the R form or relaxed form) ?

Which of the following is a function of the polypeptide of myoglobin?

Which of the following is NOT a characteristic of hemoglobin's binding of oxygen?

Which of the following is the reason why BPG shifts the oxygen saturation curve of Hb to the right?

Which of the following mechanisms explains how carbon dioxide affects O₂ binding to Hb?

Which of the following regarding the effect of protons on binding of O₂ by hemoglobin is NOT correct?

Which of the following regarding the differences between Hb and Mb is NOT correct?

Why are we are protected to some extent against low level CO poisoning?