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What is the difference between Cooperativity and Allosteric of hemoglobin?
They both sound smiliar to me. 🙁
They both sound smiliar to me. 🙁
Hemoglobin
- Thread starter delsol7
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BodybldgDoc
Cooperativity is when a substrate binds to the active site of an enzyme subunit that in turn activates the other subunits and results in complete activation of the enzyme.
Allosterism is a change in the activity and conformation of an enzyme resulting from the binding of a substrate at a regulatory site on the enzyme that is separate from the active binding site.
Adding on to what BodybldgDoc said:
Cooperativity of Hb basically means that when oxygen binds to the active site of one subunit of hemoglobin, it makes it easier for another oxygen molecule to bind to the active site of the next subunit, and then even more favorable for binding to the 3rd subunit, and the 4th, until all four subunites are saturated with oxygen. So cooperativity allows hemoglobin to become saturated with O2.
The negative allosteric effect on Hb occurs when a negative allosteric inhibitor (2,3 BPG - but I don't think you need to know this for the DAT) binds to an allosteric site (not the active site), and causes a conformational change which decreases hemoglobin's affinity for oxygen. It's kind of the opposite of cooperativity.
Hope that was at least somewhat helpful.
What you said is absolutely correct. Binding O2 to one subunit facilitates additional binding of O2 to the other 3 substrates until all four substrates are saturated with O2. (This happens in lungs so that Hb can take up a maximum amount of O2 to transport to the rest of the body.)
However, once hemoglobin starts to deoxygenate (giving oxygen to tissues), then a negative allosteric inhibitor binds to hemoglobin (at a site other than the active site) and induces more "unloading" of O2, making it progessively easier for more and more O2 to unload to the tissues.
I apologize if I'm not explaining it well.
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http://en.wikipedia.org/wiki/Allosteric_regulation
Hopefully this should explain things better! Good luck studying!
- Donjuan
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That's same as what "BodybldgDoc" said.
Allosteric molecule requires some binding substance "other" than substrate binding site, which wiki is stateing allosteric site.
Destroyer states that once O2 binds to Hb, then it causes more O2 molecules to bind to Hb. (Destroyer stated as allosteric.) However, this sound more like cooperativity rather than allosteric.
One of the question from Achiever asked similar question. I answered cooperativity and it was correct but in destroyer it's not.
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O2 is a positive allosteric effector (activator) of Hb since the binding of O2 facilitates further binding of O2. In fact, it is 300x easier for the fourth O2 molecule to bind to Hb than for the first.
There are other allosteric effectors of Hb. The molecule 2,3-BPG is a negative allosteric effector (inhibitor). While the four subunits are each in the T state unbound to O2, there is an allosteric site in the middle of them which 2,3-BPG can bind to. Once the first O2 binds to Hb, the site closes up and 2,3-BPG does not bind there anymore. This makes it easier for subsequent O2 molecules to bind to Hb. Conversely, when the first O2 molecule comes off of Hb it makes it easier for 2,3-BPG to bind. When it binds, it shifts the dissociation curve to the right and the affinity for O2 is decreased. So more O2 will come off (dissociate).
As a side note on 2,3-BPG, fetal Hb is comprised of two subunits, alpha and gamma (as opposed to normal adult Hb which is alpha and beta). The molecule 2,3-BPG binds to the beta subunits in adults and spans this gap in the middle of the four subunits. The gamma subunits have a different amino acid in one of the positions with a different charge which makes it very unlikely that 2,3-BPG will attach there. Thus, the dissociation curve shifts way to the left and the affinity of Hb for oxygen goes way up for most partial pressures of O2. This is very important since the fetus wants to pick up as much oxygen from the mother as it can get for itself. If 2,3-BPG were able to bind to fetal Hb then it wouldn't be able to grab as much O2 from the mother.
CO2 is an allosteric inhibitor of Hb. High pH is an allosteric inhibitor of Hb. High temperature is an allosteric inhibitor of Hb (I think... someone check this one).
Cooperativity refers specifically to the fact that when one O2 molecule binds to Hb it induces a conformational change to the Hb molecule which makes it easier for further O2 binding. So the first one helps the second one which helps the third which helps the fourth.
So it's probably a matter of what book you use.
There are other allosteric effectors of Hb. The molecule 2,3-BPG is a negative allosteric effector (inhibitor). While the four subunits are each in the T state unbound to O2, there is an allosteric site in the middle of them which 2,3-BPG can bind to. Once the first O2 binds to Hb, the site closes up and 2,3-BPG does not bind there anymore. This makes it easier for subsequent O2 molecules to bind to Hb. Conversely, when the first O2 molecule comes off of Hb it makes it easier for 2,3-BPG to bind. When it binds, it shifts the dissociation curve to the right and the affinity for O2 is decreased. So more O2 will come off (dissociate).
As a side note on 2,3-BPG, fetal Hb is comprised of two subunits, alpha and gamma (as opposed to normal adult Hb which is alpha and beta). The molecule 2,3-BPG binds to the beta subunits in adults and spans this gap in the middle of the four subunits. The gamma subunits have a different amino acid in one of the positions with a different charge which makes it very unlikely that 2,3-BPG will attach there. Thus, the dissociation curve shifts way to the left and the affinity of Hb for oxygen goes way up for most partial pressures of O2. This is very important since the fetus wants to pick up as much oxygen from the mother as it can get for itself. If 2,3-BPG were able to bind to fetal Hb then it wouldn't be able to grab as much O2 from the mother.
CO2 is an allosteric inhibitor of Hb. High pH is an allosteric inhibitor of Hb. High temperature is an allosteric inhibitor of Hb (I think... someone check this one).
Cooperativity refers specifically to the fact that when one O2 molecule binds to Hb it induces a conformational change to the Hb molecule which makes it easier for further O2 binding. So the first one helps the second one which helps the third which helps the fourth.
So it's probably a matter of what book you use.
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I thought it was 200 x easier 😉 jk.
As streetwolf said, Hb has a T and a R state so it is allosteric in that it changes confirmation depending on what is bound to it (remember oxygen isn't the only substrate that can bind Hb.)
As streetwolf said, Hb has a T and a R state so it is allosteric in that it changes confirmation depending on what is bound to it (remember oxygen isn't the only substrate that can bind Hb.)
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Thank you very much for all your answers. I'm definately getting clear on this subject however we are still talking about same thing in different words.
So, if question asks, O2 binds to Hb, we see an increased affinity for O2 binding in the remaining subunits. This is called... Cooperativity or Allosteric effect?
According to all of you guys, allosteric effect has to do with some other substance 2,3-BPG, which is negative allosteric inhibitor. Here we are talking about increased affinity so we are not talking about allosteric inhibitor.
The question sounds more like "when one O2 molecule binds to Hb it induces a conformational change to the Hb molecule which makes it easier for further O2 binding." So, it must be Cooperativity!
Destroyer is wrong! 😀
So, if question asks, O2 binds to Hb, we see an increased affinity for O2 binding in the remaining subunits. This is called... Cooperativity or Allosteric effect?
According to all of you guys, allosteric effect has to do with some other substance 2,3-BPG, which is negative allosteric inhibitor. Here we are talking about increased affinity so we are not talking about allosteric inhibitor.
The question sounds more like "when one O2 molecule binds to Hb it induces a conformational change to the Hb molecule which makes it easier for further O2 binding." So, it must be Cooperativity!
Destroyer is wrong! 😀
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Let's set everything straight.
Coopertivity occurs when Oxygen (can be others) binds to the heme group of hemoglobin. This causes a confirmational change in the subunits of HB (T state to R state to be specific.) The R state of hemoglobin (has O2 bound) has a much higher affinity for more oxygens than the unbound state due to the confirmational change. Cooperativity is a type of allosteric effect. Not all allosteric effects are inhibitory (hence why it is called allosteric INHIBITION when dealing with inhibitory effects.) Hemoglobin is an allosteric molecule.
Coopertivity occurs when Oxygen (can be others) binds to the heme group of hemoglobin. This causes a confirmational change in the subunits of HB (T state to R state to be specific.) The R state of hemoglobin (has O2 bound) has a much higher affinity for more oxygens than the unbound state due to the confirmational change. Cooperativity is a type of allosteric effect. Not all allosteric effects are inhibitory (hence why it is called allosteric INHIBITION when dealing with inhibitory effects.) Hemoglobin is an allosteric molecule.
B
BodybldgDoc
Hemoglobin is an allosteric molecule that becomes activated or inhibited through the cooperative process where one subunit leads to the activation or inhibition of other subunits by either a positive modulator or negative inhibitor binding to the allosteric site.
I dont know why everyone is giving you more info that you really need and confusing you. Forget about the T and R state and 2,3 BPG and all that stuff, you will never encounter this on the DAT. To keep it simple Just keep in mind the definition of allosterism and how cooperativity works. /end
heres a link that might help, http://www.nd.edu/~aseriann/knf.html
pay attention to the KNF model
I dont know why everyone is giving you more info that you really need and confusing you. Forget about the T and R state and 2,3 BPG and all that stuff, you will never encounter this on the DAT. To keep it simple Just keep in mind the definition of allosterism and how cooperativity works. /end
heres a link that might help, http://www.nd.edu/~aseriann/knf.html
pay attention to the KNF model
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Ok, I totally understand all. 😀
If you were to answer this question, what's your answer then?
O2 binds to Hb, we see an increased affinity for O2 binding in the remaining subunits. This is called... Cooperativity or Allosteric effect?
No explanation needed. Just simply answer. That's what I wanted from the start. I didn't know it was going to be this long discussion.
If you were to answer this question, what's your answer then?
O2 binds to Hb, we see an increased affinity for O2 binding in the remaining subunits. This is called... Cooperativity or Allosteric effect?
No explanation needed. Just simply answer. That's what I wanted from the start. I didn't know it was going to be this long discussion.
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Both are good answers but this is a test where you must choose THE BEST and most SPECIFIC answer so I would go with cooperativity. Allosteric is still correct but it isn't the best answer.
