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Altius test 2 Biological Section Passage 8 Question 43
Micaela_5142
#1 Posted : Thursday, July 09, 2020 10:42:04 PM
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This question asks what would happen to the pKa values of the cysteine and histidine residues in the ADH active site, and the explanation of the correct answer stated that the Zn2+ destabilizes the protonated form of the amino acids, making the proton more acidic, but I don't understand how or why this would happen. Why would the amino acids have lower pKa values in the active site?
INSTR_Katerina_102
#2 Posted : Monday, July 13, 2020 5:22:27 PM
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Hi Micaela,

Attached is a drawn explanation https://ibb.co/qYS2FVY.

My engineering friends always bugged me telling me that chem was applied physics (and in some ways this is pretty true).

Using coloumb's law from physics, we know that + charges repel + charges, destabilizing molecules. In this case, the Zn2+ being close to the highly positive protons will acidify them, and stabilize the negative conjugate bases (as - stabilizes +).

Please let me know if this is unclear.

Katt
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