4a. If you had a cysteine side chain in a protein such that it was in the enviro

Question

4a. If you had a cysteine side chain in a protein such that it was in the environment shown below, what would you expect to be true about the pKa value for this side chain knowing that the literature value for this side chain's pKa value is 8.5. Would you expect the pKa to be higher, lower or the same as the literature value? Explain in 2 sentences of less your reasoning for the pKa of this cysteine side chain. /y NOTE: the thick black line here represents the peptide backbone and not all amino acids present in this protein are shown. Only the cysteine and another amino acid side chain are shown 4b. If you had a histidine amino acid side chain surrounded by non-polar amino acids in a protein, what would you expect to be true about the pKa value for this side chain knowing that the literature value for this side chain's pKa value is 6 Would you expect the pKa to be higher, lower or the same as the literature value? Explain in 2 sentences of less your reasoning for the pKa of the histidine side chain.

Explanation / Answer

The SH group would denote its hydrogen to the neighbouring side chain and thus pka value of cystein would increase.

In case of histidine in a non polar environment it would become a neutral species its pka would decrease and thus it can act as a hydrogen acceptor.

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