Question

3.

Which of the following statements is NOT an explanation for how oxygen is released from oxy-haemoglobin.

Select one:

A.
Carbon dioxide has a stronger affinity than oxygen to heme, and displaces oxygen in tissues.

B.
Formation of carbonic acid lowers the oxygen affinity of haemoglobin in tissues.

C.
The structure of deoxyhemoglobin is stabilized by the interaction with BPG.

D.
Salt bridges are formed with N-terminal carbamates in deoxyhemoglobin.

E.
Salt bridges are formed between acidic and basic side chains of His146 and Asp94, respectively in deoxyhemoglobin .

4.

Which of the following description of hemoglobin S (HbS) forming fibrous aggregates is FALSE?

Select one:

A.
Valine at position 6 of the β chains form hydrophobic interaction with other HbS.

B.
Formation of aggregates occurs more severely in homozygotes, i.e. both alleles carrying the mutation.

C.
The aggregates distort the shape of the red blood cells.

D.
Formation of aggregates occurs only in deoxygenated form of HbS.

E.
More aggregates are formed in lungs.

Answer 1

Answer of question 1.- Statement one is correct option as it is not the correct explanation

A The first statement is wrong and not a correct explanation as carbon di oxide does not compete with oxygen for the same heme sites. When carbon di oxide binds with Hb it binds at amino group forming carbamino compound

B The second statement is true as formation of carbonate ion releases H+ and shifts the bohr curve in right direction and stabilizes the Tau form in the tissue. Tau form of Hb has less affinity for oxygen hence it releases oxygen in tissues. Hence this statement is correct.explanation

C . BPG stabilizes deoxyhemoglobin and favours Tau state formation which pushes the bohr curve in right direction and decreases the affinity of Hb for oxygen and hence favours release of oxygen in tissues. The statement is correct explanation.

.

D. The CO2 binds with Hb by forming carbamino compound. CO2 binding on amino terminal akes the amino terminal negative . This negative charge gavours salt bridge formation between both the chains of Hb. Hence this is also correct explanation.

E. The salt bridge formation between Asp94 and His146 residue happens when pH decreases in deoxyhemoglobin and Tau form of hemoglobin with weak affinity for hemoglobin is stabilized.Hence this is also correct explanation.

Question 4. The correct option and False description is statement E

Answer.

A Statement one is correct because sickle cell anaemia happens due to point mutation when Glutamic acid (a polar amino acid ) is replaced with valine ( a non polar) and generates a hydrophobic patch. and Hb A is converted to HbS. Under normal condition the patient does not feels any problem. However under hypoxic condition the deoxy form of Hb exposes a hydrophopic patch and polymerizes into a fibrous precipitate,

B Formation of aggregates happens more severely in homozygotes as 100 % Hb in this scenario will be of HbS type. In heterozygous condition (Carrier -Sickle cell trait) 50 % Hb remains of normal type (HbA) and hence condition does not become deadly in hypoxic scenario. This statement is also true

C. This statement is also correct as due to polymerization the shape of RBC is distorted into shape of sickle (hence the name of disease,)

D This statement is also correct as only deoxyhemoglobin exposes the hydrophobic patch necessary for polymerization and precipitation into the form of aggregates. Nothing of this sort happens in oxygenated hemoglobin

E. This statement is wrong as more aggregates are formed in deoxygenated condition and hence in tissue rather than lungs which contains mostly oxygenated blood hence less risk of sickle cell formation