Answer of part B needed MasteringChemistry: Extra credit homework https:// sessi

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Answer of part B needed

MasteringChemistry: Extra credit homework https:// session mastering chemistry.com /myct/itemView?assignmentProblem ID 67805283 Biochem 523 Sec01 F16 Signed in as yuhan tian l Help l Close Extra credit homework Problem 5.18 Resources previous l 3 of 7 l next Problem 5.18 You have discovered a novel protein that has a pI 5.5. To study the functional properties of this new protein, your research group has made a mutant that contains two amino acid changes-namely, a surface Phe residue in the normal protein has been replaced by His (side chain pKa 6.1), and a surface Gln has been replaced by Glu (side chain pKa 6.0 Part A Is the pl of the mutant protein predicted to be greater than, less than, or the same as the pl of the normal protein? The pl of the mutant protein predicted to be greater than the pIof the normal protein. The pl of the mutant protein predicted to be the same as the pl of the normal protein. The pl of the mutant protein predicted to be less than the pl of the normal protein. Submit My Answers Give Up Correct Part B Support your answer with the calculation of an overall charge on the mutant at pH 5.5 Express your answer using three decimal places

Explanation / Answer

At pH 5.5, His will be positively charged as it pKa is 6.1, higher than th pH. While Glu has pKa of 6.0, also above the pH, so it also retains proton. Here I would like to mention that the details in question is wrong as Glu being an acidic amino acid can never have pKa of 6.0, it is actually around 4.0.

So, at pH 5.5, Glu doesn’t has overall charge. His will be +1. The pI of normal protein being 5.5 is originally overall neutral at this pH. Thus, mutant charge at pH 5.5 is +1.000

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