The question
Name: ______________________ Date: ____________ A side chain in the core of an enzyme (4 points)
Experimental setup
A side chain in the core of an enzyme
An enzyme that works dissolved in the watery fluid inside cells folds into a compact shape. Position 88 of its polypeptide is valine, whose side chain is nonpolar, and in the folded enzyme this side chain is buried in the center of the molecule. Researchers compare the normal enzyme with two versions made from altered genes: in one, valine 88 is replaced by glutamic acid (a negatively charged side chain); in the other, by isoleucine (a nonpolar side chain slightly larger than valine's).
(a) Describe where nonpolar side chains are usually found in a folded protein that works in water, and why. [1 point]
(b) Explain how replacing valine 88 with glutamic acid would affect the enzyme's tertiary structure. [1 point]
(c) Predict the effect of the glutamic acid replacement on the enzyme's function, and justify your prediction. [1 point]
(d) Explain why replacing valine 88 with isoleucine is likely to have little effect on the enzyme's function. [1 point]