SPOILER: AAMC (Unscored) Sample FL BB Q23

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Jun 14, 2020
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I'm confused about this question because I recall the oxygen–hemoglobin dissociation curve and thought that, just like hemoglobin's affinity to oxygen decreases in low-oxygen condition, a transporter enzyme's affinity to a nutrient substrate (L-alanine) would decrease under low-food condition. That's why I chose B and I was wrong. Why are these two cases different? Sidenote: unlike hemoglobin, the Kt of this transporter enzyme in the passage does not change, so its affinity to substrate does not change.
The passage is attached below. Thank you!!
Which feature of the kinetics of L-alanine transport would provide evidence that DOM is an important source of nutrients under low-food conditions?
  • A. (Correct)
    High-affinity transport (Kt) of L-alanine
  • B. (My original answer)
    Low-affinity transport (Kt) of L-alanine
  • C.
    High transport capacity (Jmax) of L-alanine
  • D.
    Low transport capacity (Jmax) of L-alanine

Solution: The correct answer is A.

This is a Biochemistry questions that falls under content category “Assemblies of molecules, cells, and groups of cells within single cellular and multicellular organisms.” The answer to this question is A because under low-food conditions, the capacity of transport is irrelevant as no transporters are saturated with L-alanine. However, the transporter’s affinity for L-alanine would be important as only high affinity transporters would be able to facilitate L-alanine uptake at low concentrations. It is a Scientific Reasoning and Problem Solving question because you are asked to apply knowledge of transport kinetics to make a prediction about what features of transport would be important under low L-alanine conditions.





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Feb 5, 2020
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Hb is a bad analogy to DOM transport. The association between Hb and O2 is cooperativity which is different from transporting food sources. A better analogy would be the difference in Km to glucose between hexokinase and glucokinase (look It up). In nutrient poor condition, you need high affinity of DOM transport so that the organism can take as much L-alanine from the environment as possible. Low Kt would do the opposite. Hope that makes sense.
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