Why Does Hemoglobin Attach Easier to CO?

[STAii]

Now here is the question.
We know that CO is a toxic substance if inhaled, But why ?
The explanation i heard said that haemoglobin gets attached easier to CO than O2 (note: the subscript option does not seem to work) , Is that right ? And why ?
I asked that question to my chemics teacher, he said that the mass of 1 mole of CO is less than the mass of 1 mole of O2 , therefore haemoglobin prefers to get attached to CO, but this does not really seem like a scientifical explanation to me (specially with word prefers in the middle).
Thanks in advance.

BTW, good nick name Monique

Edited for the spelling mistake noted by Jikx

 

[Jikx]

its actually haemoglobin.

here's a little something i pulled from google.com (mainly because i remember something vaguely about CO having a lower latent energy to combine with haemoglobin than O2, hence is favoured ).

To explain this aspect, we need to explain how the body uses oxygen from the air. Oxygen is transported around the body via the red blood cells. Specifically, oxygen binds to a substance within the red blood cells called haemoglobin, which is also responsible for their red colour.
Haemoglobin takes up oxygen as blood passes through the lungs, and at the same time carbon dioxide, produced by the body's metabolism, is released from the blood into the exhaled breath. The combination of oxygen with haemoglobin is called oxyhaemoglobin and this 'oxygenated' blood is carried away from the lungs through the bloodstream to all the tissues of the body.

Carbon monoxide can also bind to haemoglobin but does so about 240 times more tightly than oxygen, forming a compound called carboxyhaemoglobin. This means that if both carbon monoxide and oxygen are inhaled, carbon monoxide will preferentially bind to haemoglobin. This reduces the amount of haemoglobin available to bind to oxygen, so the body and tissues become starved of oxygen.

Carboxyhaemoglobin also has direct effects on the blood vessels of the body - causing them to become 'leaky'. This is seen especially in the brain, causing the brain to swell, leading to unconsciousness and neurological damage.

http://www.netdoctor.co.uk/health_advice/facts/carbonmonoxide.htm

 

[STAii]

Thanks Jikx.
But what i really need to know about is this

Carbon monoxide can also bind to haemoglobin but does so about 240 times more tightly than oxygen

I need a chemical explanation for that !
Anyone ?

 

[damgo]

It's a big protein, and folds up in a complicated way. There is a particular area where the oxygen/CO/CO2 can "fit" determined by the shape of hemoglobin, its charge distribution, and maybe other stuff. CO happens to fit much better than O2, apparently...

On an cool side note, your brain actually produces CO (and NO) in small quantities and uses them as a special kind of neurotransmitter!

 

[FZ+]

Hmm... I would have thought it was something to do with the stability of the CO molecule in comparison to the O2...
Well, what do I know?!

 

[Monique]

Did you realize that it actually makes evolutionary sense that O2 doesn't bind to tightly to haemoglobin?

 

[STAii]

Originally posted by Monique
Did you realize that it actually makes evolutionary sense that O2 doesn't bind to tightly to haemoglobin?

Can you explain a little bit more please ?

 

[Monique]

Well, the reason that oxygen doesn't bind to haemoglobin very strongly is that the oxygen should be released in an environment where the oxygen concentration is low. Just strongly enough to take it up, but not too strong so that it doesn't let go.

I remember a few years ago where I actually had to do the calculations of these interactions.. curves etc.

 

[STAii]

Frankly Monique, i didn't get what you are talking about.
Now you are breating.
You take the oxygen into your lungs, it gets attached to the haemoglobin.
The haemoglobin runs in the blood, the oxygen is used by the cells, other gasses are take back to the lungs by the haemoglobin.

Where comes the part where you have to take oxygen from haemoglobin back to the environment ?

 

[FZ+]

The haemoglobin runs in the blood, the oxygen is used by the cells

There you go. At this point, the oxygen must be able to leave the haemoglobin and diffuse into the cells, where it is used in reactions. If like CO, it binds too tightly to the haemoglobin, it can never get to the cells.

 

[Monique]

Correct, diffusion is the key. The bindingstrength and oxygen partial pressure have to be fine-tuned, so that the oxygen will come off the complex when the oxygen concentration is cells is below a certain value, but it will stay attached if the cells don't need oxygen.

 

[STAii]

Ahh, i thought you were talking about oxygen concentration in Air.
Dumb me !