Biochem Practice Question

[yui_96]

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Adding concentrated strong base to a solution containing an enzyme often reduces enzyme activity to zero. In addition to causing protein denaturation, which of the following is another plausible reason for the loss of enzyme activity?

A. Enzyme activity, once lost, cannot be recovered
B. The base can cleave peptide residues
C. Adding a base catalyzes protein polymerization
D. Adding a base tends to deprotonate amino acids on the surface of proteins.

I understand that B is the correct answer because base can catalyze hydrolysis of peptide bonds. However, I wonder what process is protein polymerization. Would that be similar to dehydration? Can base also catalyze dehydration process (it's been a long time since I took organic chemistry)?

 

[BerkReviewTeach]

To answer your question, as opposed to their question, polymerization is the addition of many smaller subunits into an overall macromolecule. So, would adding OH- to a protein make a structure that has TWO reactive ends that can connect to other structures with TWO reactive ends? Creating an environment rich is negative charge is not likely to create a polymer-forming environment. A small catalytic amount could potential cause such a reaction, but the question emphasizes "concentrated" in the wording.

Depending on the molecule, dehydration can occur with either base catalysis or acid catalysis. It is likely that you will either get pi-bonds forming (elimination reactions) or linkages formed (such as the beta and alpha glycosidic linkages in polysaccharides.) Generally speaking, you do not need high concentrations of a catalyst to carry such reactions out, so the term "concentrated" in the question stem is an indicator that we are looking for something other than a catalytic process.

 

[aldol16]

Polymerization in this context is the polymerization of amino acid residues to make a polypeptide. These reactions are also classified as dehydration reactions because the condensation of two residues liberates a water molecule (nucleophilic attack of an amine on a carboxylic acid).