AS Biology Helpp! - Haemoglobin

Hello,
I've recently done Haemoglobin in class and I don't really understand the different dissociation curves for normal, fetus' and myoglobin . If someone could explain these plus haemoglobin in general please help! Thanks!!

Normal haemoglobin has this 'S' shape curve which is the norm. At low O₂ partial pressure (pp), haemoglobin readily unloads oxygen. This is in the case of respiring cells which need oxygen.
At high O₂ pp, haemoglobin readily loads oxygen. This is in the case in the lungs where there's plenty of oxygen and it needs to be saturated with it.

Compare that to myoglobin, you can see that at myoglobin is normally loaded with oxygen at most O₂ pp.

Only at very very low O₂ pp does the affinity for oxygen change. Thus, myoglobin unloads oxygen to cells which have a critically low amount of oxygen. This is usually in the case of muscle cells which are respiring during strenuous exercise and are building up an oxygen debt.

So if you treat the haemoglobin curve as the norm, then curves that shift to the left indicate that they will have a higher affinity for oxygen and readily associates with oxygen. They will only dissociate with the oxygen at low O₂ pp
So we can deduce that foetus needs a higher affinity for oxygen than it's mother. Why? Well, it's not exposed to air. So it's going to have to get it's oxygen from the blood of the mother. This is harder for two reasons: there's not as much oxygen as there is in the air obviously, there's a membrane between the blood vessels of the foetus and mother making uptake very difficult. Thus it wants to hang onto that oxygen.

That image sucks sorry and I can't get rid of it...

http://www.s-cool.co.uk/assets/learn_its/alevel/biology/transport/blood/2008-01-22_114556.gif

Normal haemoglobin has this 'S' shape curve which is the norm. At low O₂ partial pressure (pp), haemoglobin readily unloads oxygen. This is in the case of respiring cells which need oxygen.
At high O₂ pp, haemoglobin readily loads oxygen. This is in the case in the lungs where there's plenty of oxygen and it needs to be saturated with it.

Compare that to myoglobin, you can see that at myoglobin is normally loaded with oxygen at most O₂ pp.

Only at very very low O₂ pp does the affinity for oxygen change. Thus, myoglobin unloads oxygen to cells which have a critically low amount of oxygen. This is usually in the case of muscle cells which are respiring during strenuous exercise and are building up an oxygen debt.

So if you treat the haemoglobin curve as the norm, then curves that shift to the left indicate that they will have a higher affinity for oxygen and readily associates with oxygen. They will only dissociate with the oxygen at low O₂ pp
So we can deduce that foetus needs a higher affinity for oxygen than it's mother. Why? Well, it's not exposed to air. So it's going to have to get it's oxygen from the blood of the mother. This is harder for two reasons: there's not as much oxygen as there is in the air obviously, there's a membrane between the blood vessels of the foetus and mother making uptake very difficult. Thus it wants to hang onto that oxygen.

That image sucks sorry and I can't get rid of it...

http://www.s-cool.co.uk/assets/learn_its/alevel/biology/transport/blood/2008-01-22_114556.gif

If the curve moves to the right how can this be an advantage for an animal??

Most animals who have dissociation curves are living in environments where there is plentiful oxygen and they are very active.

Because they are very active, the haemoglobin needs to unload oxygen more readily to the cells so that it can meet the demands of aerobic respiration.

If they are active and the sigmoid curve is too the left, then what that's saying is that the haemoglobin will readily load oxygen but only unload them in very low partial pressures of oxygen.

Firstly, there's no need to have such a high affinity for oxygen in a very oxygenated environment.

But secondly, the animal is going to have a high rate of respiration and it preferably it would like a modest partial pressure of oxygen in the cells. It does not want to have to aerobically respire so much to get the oxygen. Instead, why not get the haemoglobin to unload the oxygen at a medium partial pressure of oxygen?

Most animals who have dissociation curves are living in environments where there is plentiful oxygen and they are very active.

Because they are very active, the haemoglobin needs to unload oxygen more readily to the cells so that it can meet the demands of aerobic respiration.

If they are active and the sigmoid curve is too the left, then what that's saying is that the haemoglobin will readily load oxygen but only unload them in very low partial pressures of oxygen.

Firstly, there's no need to have such a high affinity for oxygen in a very oxygenated environment.

But secondly, the animal is going to have a high rate of respiration and it preferably it would like a modest partial pressure of oxygen in the cells. It does not want to have to aerobically respire so much to get the oxygen. Instead, why not get the haemoglobin to unload the oxygen at a medium partial pressure of oxygen?

Most animals who have dissociation curves are living in environments where there is plentiful oxygen and they are very active.

Because they are very active, the haemoglobin needs to unload oxygen more readily to the cells so that it can meet the demands of aerobic respiration.

If they are active and the sigmoid curve is too the left, then what that's saying is that the haemoglobin will readily load oxygen but only unload them in very low partial pressures of oxygen.

Firstly, there's no need to have such a high affinity for oxygen in a very oxygenated environment.

But secondly, the animal is going to have a high rate of respiration and it preferably it would like a modest partial pressure of oxygen in the cells. It does not want to have to aerobically respire so much to get the oxygen. Instead, why not get the haemoglobin to unload the oxygen at a medium partial pressure of oxygen?

How does this link into temperature, for a higher temperature the curve moves to the right but what is an advantage of this?? Sorry for so many questions !! hahaa
Thanks!

And does an increase in respiration rate in the tissues of a mammal move the curve the right ??

You're right at a higher temperature the curve moves to the right. Temperature has a smaller effect than pH or concentration has on the curve. I guess an advantage of this is that if you think of animals with a high internal core temperature, they will need more oxygen for respiration to maintain this core body temperature.

Think of a little mouse. It has a high surface area to volume ratio so it's going to be losing a lot of heat and so in turn its going to have to kee its core body temperature high. The mouse's haemoglobin will unload oxygen more readily to the cells to maintain a high rate of respiration.

Another advantage I can think of is like a positive feedback mechanism. Say you had hypothermia and we go ahead and warm you up with a space blanket. As you begin to warm up, the oxygen dissociation curve shifts more to the right allowing more oxygen to be unloaded to cells. This increases the rate of respiration which increases your body temperature even more. In turn this shifts the curve even more to the right, and so on; the net effect is that you get warmed up. Of course there is a limit, the curve doesn't just keep shifting to the right.



Yes you're right, a higher respiration rate moves the curve to the right as the cells need more oxygen.
In fact, if you want a more concrete answer, it's not just that the oxygen supply is running low, but it's more because that the concentration of CO₂ in the blood is increasing.
CO₂ is an acidic gas and when it dissolves into the bloodplasma it will lower the pH (not by much, probably about 4-6). As you know, pH is one of the factors that affects proteins and enzymes, causing them to denature. In this case, the lower pH means that the quaternary structure of haemoglobin is affected; this makes oxygen more readily unloaded to cells. This is called the Bohr Effect.