2+ Year Member
Jan 9, 2016
Medical Student (Accepted)
I just don't get this question...Why would aconitase release Fe-S under low iron condition when it also wants to preserve intramolecular iron?

Can anyone also explain why I is false?

Answer is B.
Blowing up all your threads.

It doesn't state that Fe-S is released into the blood stream, just that the co-factor is released from the enzyme. There is a protein within the cell that appears to function as an intracellular iron holder caller ferritin, which, if I was to make unsupported reaching assumptions, might hold onto this iron. Then, the IRP can influence translation to upregulate receptors and increase iron concentration within the cell. Anyways, your goal here is to elludicate the correct answer choice and not get bogged down in specifics too much.

I would say the easiest way to come to the answer is the process of elimination. Option II is patently false, as the second diagram shows that IRP-2 is broken down, not converted into IRP-1, which gets rid of D. The remaining options sound similar, but are actually quite different. As stated in the passage, transferrin is a transport protein found in the blood aka extracellularly. As intracellular proteins, IRPs would not generally cross the cellular membrane and have wide reaching effects on the circulatory regulation, which rules out option 1. Option three sounds feasible, however, as this would exhibit local control in the cellular cytosol, which is definitely viable for a peptide. More so, this effect is mentioned in the passage in the last sentence of the second paragraph under the first diagram.

Hope this helps!