AAMC section bank c/p #75

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jennieblackpink

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how do they know to choose the answer with respect to ATP instead of galactose? Is it just whatever gets you the biggest k_cat/K_M value?

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how do they know to choose the answer with respect to ATP instead of galactose? Is it just whatever gets you the biggest k_cat/K_M value?

Yep. The question asks to find the highest catalytic efficiency, which is defined as kcat/KM. There are two ways to increase catalytic efficiency: increase kcat or decrease KM. Table 1 shows kcat is highest for WT/wild-type, and it also shows that KM is lower for ATP than for galactose.

So the highest catalytic efficiency is for wild-type GalK with ATP substrate.

By the way, the answer choices help us avoid doing calculations since it doesn’t list D45G has an option. This allows us to compare fractions of similar magnitudes without having to do the math.
 
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