My question is based on Biochemistry

Question

20) Binding of oxygen to Fe2+ of heme group leads to 

a	Flattening of Heme
b	Increased binding of DPG
c	Formation of salt bridges
d	All options are true

19) Smokers are known to have an increased concentration of DPG. This helps in

a	A higher saturation of oxygen binding to myoglobin
b	A small decrease in oxygen binding in muscles
c	A large decrease in oxygen binding in muscles
d	An improved oxygen binding efficiency in lungs

18) A mutation of Lysine 82 (in the DPG-binding pocket) to Arginine in beta sub-unit will most likely result in 

a	Higher than normal binding affinity to oxygen
b	Not enough information
c	Normal binding to oxygen
d	Lower than normal binding affinity to oxygen

17) After exhalation of carbon dioxide, His 146 becomes  ___________________ , resulting in ________________ oxygen binding affinity by hemoglobin.

a	Protonated, Increased
b	Deprotonated, Increased
c	Protonated, Increased
d	Deprotonated, Decreased

16) Which of the following facts are true when CO binds to HB

a	Binding of CO to HB leads to formation of relaxed state of the quaternary structure
b	Binding of CO to HB is reversible
c	Binding of CO to HB improves oxygen release in muscles
d	Binding of CO has no effect on HB structure

15) Which of the following statements is untrue?

a	Smokers have a very low level of DPG so that oxygen can easily bind to HB
b	Concentration of DPG increases at high altitudes
c	DPG makes oxygen binding to HB difficult
d	DPG is an allosteric inhibitor of oxygen binding to HB

Answer 1

20:

Hemoglobin has two states: T (tense) and R (relaxed), T has a lower affinity for oxygen than R and is used to release oxygen throughout the bloodstream. R is used when absorbing oxygen in the lungs.

a. Flattening of Heme: correct answer, when oxygen is absorbed, hemoglobin becomes planar (relaxed)

b. Increased binding of DPG: incorrect answer, DPG binds with deoxygenated hemoglobin

c. Formation of salt bridges: incorrect answer: Salt bridges are only present in the T state, which is deoxygenated.

19:

DPG aids in releasing oxygen into the bloodstream by bonding to deoxygenated blood therefore helping hemoglobin release oxygen. It definitely would not help with oxygen uptake in the lungs, so it's not d. If more oxygen is being forced out of RBC in the bloodstream, it must allow for muscle tissues to uptake more. Therefore it is not b or c. The answer must be a, because by forcing hemoglobin to release more oxygen, it allows more absorption of oxygen into the cells. This makes sense as smokers have reduced oxygen uptake due to damaged lungs so their body must compensate by forcing hemoglobin to release more oxygen to the muscles than a healthy person would need.

18:

DPG is a polar molecule, so the space in which it binds needs to be polar as well. While arginine and lysine are both polar, arginine is more polar and therefore would bind DPG better than lysine would. Because DPG would bind more strongly, this would decrease oxygen affinity as DPG favors deoxygenated hemoglobin. The answer is d

17:

The histidines in hemoglobin play several roles. First, they act as pH buffers as CO₂ dissolved in blood will react to form carbonic acid and release H⁺ ions, causing the blood to become acidic. Histidines become protonated to absorb these excess protons, which are then released in the lungs, combined back with carbonic acid, and released as CO₂. His₁₄₆ in particular is used to form the salt bridge that holds the hemoglobin in the T state (low oxygen affinity) and once the hemoglobin reaches the lungs, becomes deprotonated and allows the hemoglobin to enter the R state. The answer is b

16:

Carbon monoxide is so deadly because it has a much higher binding affinity than oxygen, meaning once it binds to hemoglobin, it is much harder to get off, and will preferentially bind over oxygen. This high binding affinity also causes the hemoglobin to become trapped in the relaxed state meaning it is unable to release oxygen into the bloodstream. This process is also irreversible, however because it is competitive inhibition, increasing oxygen concentration can cause the carbon monoxide to be released. Therefore the answer is a.

15:

DPG works by allosterically inhibiting oxygen uptake by hemoglobin, meaning it binds to hemoglobin and prevents oxygen from binding (this means c and d are correct). DPG accumulates in people with long term hypoxic (low oxygen) conditions, such as being in high altitudes or smokers. This forces oxygen to be released into the tissues and therefore allows more oxygen to be carried throughout the body. DPG would be in higher concentrations at high altitude so b is also correct. The answer is a because smokers create a hypoxic environment in their body by damaging their lungs and inhaling carbon monoxide produced from incomplete burning of tobacco.