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Old 07-24-2013
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RBC Oxygen Dissociation Curve of Beta Subunits-Only Hemoglobin

Can someone plz explain this question :

Imagine that hemoglobin beta-subunits were dissociated from the alpha-subunits. If a solution formed by only monomeric beta subunits is created, it's oxygen dissociation curve will shift to what side (right or left) and why.

Can someone plz explain this question.
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Old 07-24-2013
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the oxygen dissociation curve exhibits positive cooperativity ....the first oxygen molecule increases affinity for the next Oxygen molecule ....

so if you separate the subunits .... then you will lose this positive cooperativity feature ....hence the curve should move to the right ....

correct me if i am wrong .....
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Quote:
Originally Posted by npktun View Post
the oxygen dissociation curve exhibits positive cooperativity ....the first oxygen molecule increases affinity for the next Oxygen molecule ....

so if you seperate the subunits .... then you will loose this positive cooperativity feature ....hence the curve should move to the right ....

correct me if i am wrong .....
I was kinda thinking along same lines. But it's something different. I'm just hoping someone will explain what this question means in first place, I'll write the correct answer soon anyways. Waiting for few more responses if someone has some idea.
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okay hows this for a theory - because there arent any alpha sub-units the cooperativity is not present. so if its a dissociative curve i guess it just has a linear graph like a myoglobin would have ?
i could be way off but im just making wild guesses here but if a side had to be picked i would pick right .
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Old 07-25-2013
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Quote:
Originally Posted by samren17 View Post
okay hows this for a theory - because there arent any alpha sub-units the cooperativity is not present.so if its a dissociative curve i guess it just has a linear graph like a myoglobin would have ?
i could be way off but im just making wild guesses here.but if a side had to be picked i would pick right .
Yeah i too thought of this one after posting..... it could be a legitimate one .... then it should follow the same affinity as Myoglobin ... and the curve should go to the left ..... myoglobin has a single polypeptide chain that behaves as a B-subunit

Quote:
Originally Posted by Thrax_usmle View Post
Can someone plz explain this question :

Imagine that hemoglobin beta-subunits were dissociated from the alpha-subunits. If a solution formed by only monomeric beta subunits is created, it's oxygen dissociation curve will shift to what side (right or left) and why.

Can someone plz explain this question.
Hemoglobin is made up of 4 chains = 2 alpha and 2 Beta .... we also call them Alpha and Beta Subunits ..... normally alpha subunit pairs with a beta subunit ....so this question states if we were to break this alpha-beta bond ....there will be individual subunits of alpha and beta subunits .... now beta subunits are solely pick to form a solution which has individual beta subunit only .... now it asks what will be its affinity as compared to hemoglobin ....

Remember when we go right in an Oxygen dissociation curve = Affinity decrease
and vice versa
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Old 07-25-2013
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Correct Answer Answer

Quote:
Originally Posted by npktun View Post
Yeah i too thought of this one after posting..... it could be a legitimate one .... then it should follow the same affinity as Myoglobin ... and the curve should go to the left ..... myoglobin has a single polypeptide chain that behaves as a B-subunit



Hemoglobin is made up of 4 chains = 2 alpha and 2 Beta .... we also call them Alpha and Beta Subunits ..... normally alpha subunit pairs with a beta subunit ....so this question states if we were to break this alpha-beta bond ....there will be individual subunits of alpha and beta subunits .... now beta subunits are solely pick to form a solution which has individual beta subunit only .... now it asks what will be its affinity as compared to hemoglobin ....

Remember when we go right in an Oxygen dissociation curve = Affinity decrease
and vice versa
Yes. If separated the subunits will demonstrate a hyperbolic oxygen dissociation curve similar to that of myoglobin. Myoglobin is a monomeric protein and primary oxygen carrying protein of skeletal and cardiac muscles. The secondary, tertiary structures of myoglobin and the beta subunits of hemoglobin are almost identical. (From the explanation in Qbank)

Myoglobin has much higher affinity for oxygen and has only one heme molecule. As it does not experience heme-heme interactions, it's oxygen diss. curve is hyperbolic and NOT sigmoid.
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hey guys
so is the answer that it will be a hyperbolic curve or is the question asking which side it shifts it?
my understanding is that for HB if it shifts to the right - lesser affinity for O2 - so it dissociates O2 - better for Tissue.
if it shifts to the left - greater affinity for O2 - associates O2 - better for loading.
so same principle for myoglobin? or is there a catch?
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Quote:
Originally Posted by samren17 View Post
hey guys
so is the answer that it will be a hyperbolic curve or is the question asking which side it shifts it?
my understanding is that for HB if it shifts to the right - lesser affinity for O2 - so it dissociates O2 - better for Tissue.
if it shifts to the left - greater affinity for O2 - associates O2 - better for loading.
so same principle for myoglobin? or is there a catch?
Myoglobin has HIGHER affinity for oxygen, so IF it were to shift, it wil shift to LEFT.
BUT Myoglobin doesnt have a sigmoid curve anyways, it is hyperbolic. Cuz there are no heme-heme interactions, as there is only ONE heme molecule in myoglobin. Unlike in hemoglobin where where one oxygen molecule attatchment leads to higher affinity for the next incoming one and so on.
So i guess they wont ask about its shifting, they will only ask about the shapes of the curve, or give a graph displaying different curves. We have to pick hyperbolic one.
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okay cool.thanks for clearing that up.
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