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NS FL Test #2 C/P Q#3

Posted: Mon Jan 28, 2019 7:05 am
by sdaswani
Hi! I was a little confused about the wording of this question. Is the figure shown below the question, the Hb dissociation curve at high altitudes? If so, how is the shape different from that at P atm? (I was thinking the shift of the curve would be to the left, as in the presence of low atmospheric O2, we'd hope for Hb-O2 binding to increase, to in turn be able to release more O2 to the tissues). This thinking seemed to resonate most with answer choice A to me.

I understand how the sigmoidal shape of the Hb-O2 dissociation curve in general is explained by cooperativity/homotropic regulation by O2, but not too sure as to why this was the answer to this specific question.

Thanks in advance for any help!
Saakshi

Re: NS FL Test #2 C/P Q#3

Posted: Mon Jan 28, 2019 8:45 am
by NS_Tutor_Will
The key with this question is in how it is phrased. If it asked about a shift in the Hb dissociation curve, then your prediction would be right in line with what the question would be looking for. Because they are asking for shape here, we definitely want our answer to deal with the curve itself and not with its relative position. So, the shape is a result of the homotropic regulation by oxygen (cooperativity). Note that this doesn't mean Hb isn't always homotropically regulated by oxygen, just that it always explains the sigmoidal shape. Further, the degree of cooperativity would be affected by pressure, so that would explain why the curve is slightly different at different pressures.

The shift is potentially relevant, it's just that it wouldn't affect the shape (but rather the position) of the Hb curve.

Hope this helps!

Re: NS FL Test #2 C/P Q#3

Posted: Mon Jan 28, 2019 9:08 am
by sdaswani
Ah, makes sense! thanks so much