Question

A genetic analysis of one of the sister

Answer 1

Carbonic anhydrase enzyme  is critical in maintaining proper acid-base balance.

Carbonic anhydrase catalyzes the reaction between water and carbon dioxide to yield carbonic acid. The carbonic acid then undergoes dissociation

H20 + CO2 ----------> H2CO3 <=========> 2H⁺ + CO₃^2-

This mutation involves substitution of Histidine amino acid [a basic amino acid] in place of tyrosine [aromatic, amino acid] at position 107.

Tyrosine

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Histidine:

Carbonic anhydrase adds two H⁺s to CO₂ so that Carbonic acid H₂CO₃ is formed. So it should be able to catalyse transfer of protons to CO2. Tyrosine has a phenolic group where phenolic proton is acidic [can be easily donated to CO2] while if tyrosine is replaced by basic amino acid Histdine which has 2 nitrogen atoms which infact accept protons from the surrounding medium to form NH⁺ ustilising lone pair electrons to form extra bond with proton [other than its usualy trivalency state].

So susbtitution of tyrosine by histidine via mutation does not let the enzyme act as as proton donor to CO2 anymore and therefore the mutation results in loss of enzymatic activity