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NS FL#2 Biology Q43

Posted: Wed Jan 30, 2019 12:27 pm
by sdaswani
Hi, I was reading through the explanation of the answer of this passage, but wanted some clarification on why there is an increase in acetyl-coA when glucose cannot be broken down in a diabetes patient. I understood the idea that when glucose cannot be taken up, the body with rely more on fatty acid metabolism, creating acetyl co-A, and ketone bodies, which is expelled in the urine. However, further below, the explanation states:

"Since insulin signaling promotes the uptake of glucose by cells, impaired insulin functioning will prevent cells from doing so, meaning that high levels of blood glucose will coexist with a state in which the cell has inadequate access to glucose for its own metabolism. If this occurs, cells may accumulate excess acetyl-CoA molecules that cannot be shunted into the citric acid cycle because the intermediaries of the citric acid cycle, especially oxaloacetate, have been siphoned off to gluconeogenesis." Why does the acetyl co-A accumulate and why can't the citric acid proceed? I also wasn't sure of the gluconeogenesis bit.

I get the idea of this question overall, and was able to answer it correctly, but was hoping to gain some more clarity on this detail as it's sometimes hard to keep track of all these processes together. Thanks so much!

Re: NS FL#2 Biology Q43

Posted: Wed Jan 30, 2019 4:15 pm
by NS_Tutor_Will
Thanks for the question! Most of this highly-specialized metabolism stuff can be a bit out of the scope of the MCAT, so don't worry too much about it. It's best to focus on the bigger picture than on the nitty gritty, but I can definitely address your question!

Essentially, because there is a lack of glucose in the cell (because it can't absorb glucose from the blood), the cell resorts to alternate means of generating glucose. One way it does this is gluconeogenesis, in which all sorts of molecules are used to create glucose (including citric acid cycle intermediaries). This has the effect of making other cycles unable to occur, since necessary components of the cycle are missing! If the CAC can't occur, then acetyl-CoA could build up because it has no cycle to enter. Acetyl-CoA is often converted into ketone bodies that can be used as fuel by the brain.

You may find it helpful to dig more into this stuff via the NS videos or the Khan videos because it'll be helpful to see the interactions between different processes. Again, though, the depth with which you might be trying to learn it may be more useful to an actual medical student rather than someone preparing for the MCAT!

In any event, I hope this is helpful!

Re: NS FL#2 Biology Q43

Posted: Sat Feb 02, 2019 7:40 pm
by sdaswani
Gotcha! And yes, I realised I was trying to think very detailed, which may not be necessary for the MCAT. Much appreciate your help/willingness to answer my questions. :)