Question 4 Hemoglobin Rainier has a mutation in the beta subunit tyr145?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????? Cys. One useful piece of information is that the residue 93 of the beta subunit is a free cysteine. The properties of this mutation in the homozygous state are as follows: (i) high O2 affinity; (ii) reduced Bohr effect; (iii) decreased affinity for BPG; (iv) low cooperativity. Explain as many of these properties of Hb as you can in terms of the structure and function of Hb. Be specific as to how the mutation relates to the observed properties. Each part is 5 marks
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This means that the mutated hemoglobin has a stronger binding affinity for oxygen molecules compared to normal hemoglobin. ** Show more…
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Hemoglobin releases protons upon oxygen binding. This phenomenon is called the Bohr effect, and an important group that participates is histidine 146 of the β subunit. In deoxyhemoglobin histidine 146 forms a salt bridge with aspartic acid 94. The salt bridge is disrupted upon oxygenation: deoxyhemoglobin oxyhemoglobin his146 asp94 asp94 his146 The pKa of the histidine side group in the deoxy form is higher than that in the free amino acid, but changes upon oxygenation of the heme Fe(II) atom. How does the pKa change (i.e., does it increase or decrease)? Why does this change occur?
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Mutations in the genes encoding the $\alpha$ and $\beta$ subunits of hemoglobin lead to blood diseases such as thalassemias and sickle-cell anemia. You have found a family in China in which some members suffer from a new genetic form of anemia. The DNA sequences at the $5^{\prime}$ end of the nontemplate strand of the normal and mutant DNA encoding the $\alpha$ subunit of hemoglobin are as follows: (a) What type of mutation is present in the mutant hemoglobin gene? (b) What are the codons in the translated portion of the mRNA transcribed from the normal and mutant genes? (c) What are the amino acid sequences of the normal and mutant polypeptides?
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