AAMC Sample Exam (Biology/Biochemistry): Question 8

[nicolaskaang]

The scientists claimed that antibody B offers a better means in preventing organ injury than agents such as free radical and protease inhibitors. Which of the following reasons offers the best support for this claim? (Correct Choice: B)
A. Antibody B is a high affinity antibody; therefore, it will not be rejected by the patient.
B. Antibody B can block the initiation of events that result in the release of harmful, biologically active molecules.
C. Antibody B is a very specific antibody; therefore, it will not recognize anything other than the beta subunit.
D. Antibody B exhibits a high half life and can be used at any dosage at any time.

Passage Details.
In the passage, a discussion of neutrophils and their effects on causing organ damage is discussed. Two membrane proteins, the alpha and beta subunit, binds to the endometrium allowing these leukocytes to migrate toward local tissues. During reperfusion, the adhering leukocytes release radicals, proteases, and prostaglandins. The beta subunit is found to be the main mediator in adhering the cell membrane of the neutrophils to the endometrium, and antibody B binds this particular subunit.

My Thinking Process.
I quickly eliminated choices A and D, and was stuck between B and C. The passage indicated that both radicals and proteases are released from these neutrophils. But wouldn't the choice of using an antibody specific to the beta subunit indicate that the antibody will not prevent other leukocytes' functions, thus specifically inhibiting the leukocytes that cause organ damage but allowing other leukocytes that release useful proteases to maintain their functions in the immune process?

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[Uncle_Drew]

I didn't read the passage, so take this fwiw, but B actually answers the question, and C just provide information about binding to the Beta subunit. What's special about the Beta subunit that would cause it to prevent organ injury? B is logically consistent - blocks harmful molecules, therefore less organ injury. Again, just a brief idea, because I didn't read the passage, but it looks like B actually answers the question.

 

[DaWeasel]

My logic in answering this question was that the antibody offered a proactive means of protection against the harmful molecules. The free radical and protease inhibitors are a response to the problem, blocking the radicals and the proteases would be better because it resolves the cause of the harmful effects. As Uncle Drew said, the specificity of the antibody does not give any reason why it is a better means of treating the problem whereas blocking the release of harmful molecules does support the claim that it is a better means of treatment.

 

[Domepiece]

You had the right idea of approaching this problem with the process of elimination. A and D are obviously wrong; C can also be excluded since it doesn't offer any support as to why antibody B would be better than other immune responses and simply states it would be highly selective for the beta subunit without qualitative effect descriptions.

The actual explanation deals with antibody B inhibiting the beta subunit, which functions in adherence and is required for the release of toxic free radicals and proteases. Since the antibody is a proactive measure before the release of harmful agents, it prevents any damage in the lag between toxic effect and administration of free radical and protease inhibitors.

Consult AAMC's explanation in the score report for their exact thought process, as it is highly detailed there. However, the important take away here is that scoring well on the MCAT is just as much about how you approach and recognize their question style as it is about outside knowledge.