21) (6 points) A hemoglobin variant V (HbV), has an aspartate residue substitute

Question

21) (6 points) A hemoglobin variant V (HbV), has an aspartate residue substituted for histidine at position 143 of the beta subunit. Residue 143 is one of the Lys 82 His 2 His 143BPG His 143 His 2 Lys 82 Central Cavity (wild type Hb) residues lining the central cavity in hemoglobin, where BPG binds. Based on the chemical properties of aspartate, how would you expect the mutation to effect BPG binding? A) Decreased affinity for BPG binding B) Increased affinity for BPG binding C) Not change affinity for BPG binding Would you expect the affinity for O2 of this hemoglobin variant to be greater than, less than, or equal to that of wild-type hemoglobin in the presence of BPG? C) Greater than A) Less than B) Equal to Would you expect the affinity for O, of this hemoglobin variant to be greater than, less than, or equal to that of wild-type hemoglobin in the absence of BPG? A) Less than B) Greater than C) Equal to

Explanation / Answer

2,3-bisphosphoglycerate (2,3-BPG) regulates the affinity of hemoglobin for oxygen and facilitates the release of oxygen to the such tissues. It helps hemoglobin transition from high affinity state for oxygen to low affinity state. 2,3-BPG only binds to the central cavity of deoxyhemoglobin with help of positively charged basic amino acids like histidine and arginine. Aspartate is an acidic amino acid. If aspartate is present in beta subuinit instead of histidine, then 2,3-BPG won’t bind with deoxyhemoglobin. It will cause increased affinity of hemoglobin for oxygen.

Question- Based on the chemical properties of aspartae, how would you expect the mutation to effect the BPG binding?

Ans- Decreased the affinity for BPG binding

Question- Would you expect the affinity for O2 of this hemoglobin variant to be greater than, less than, or equal to that of wildtype hemoglobin in the presence of BPG?

Ans-Greater than

Question- Would you expect the affinity for O2 of this hemoglobin variant to be greater than, less than, or equal to that of wildtype hemoglobin in the absence of BPG?

Ans- Equal to

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