[cheryl j (OP)]

Is the iron in haemoglobin responsible for the binding of oxygen to the molecule? Is it chemically related to things like rust, or are oxidation/reduction reactions completely different?

[CliffordK]

Yes & Maybe.
I believe it is a single iron atom, kept in ionic form, Fe²⁺ and Fe³⁺

However, I don't believe that it truly forms a covalent bond with oxygen like one would find in rust.

The iron (Fe) atom can be replaced with other metals such as lead (Pb) which leads to much lower affinity for oxygen (at least that is what I thought I had heard, I'm seeing other notes about lead and haemoglobin on the web).

[cheryl j (OP)]

well i noticed that it has almost the same structure as chlorophil only I think its magnesiium in the center of it.

[Bored chemist]

The oxygen binds to the iron in haemoglobin but it doesn't oxidise it.
The effect of lead poisoning on haemoglobin is not due to substitution by of iron by lead. It's because lead interferes with the production of the haemoglobin.
The structures of chlorophyll and haem are fairly similar. So is vitamin b12 - but it has a cobalt atom on the middle.

[cheryl j (OP)]

in this one diagram i saw, they drew a dotted line between the heme molecule and oxygen and I'm not a chemist, but the explanation said kind of vaguely that the iron atom as well as the surrounding side groups held oxygen in place.

[damocles]

For haemoglobin to do its job, it has to be able to make a suitably weak bond with oxygen molecules so that it can pick up oxygen (dioxygen gas) in one place and drop it off in another. Many metals make bonds called co-ordinate bonds (your dotted lines) that work a little differently to normal covalent bonds, and are often (but not always) weaker. The rest of the haemoglobin molecule is a protein attached to a porphyrin ring. The porphyrin ring is a big flat structure that is very similar in chlorophyll and vitamin B-12, and that can form 4 co-ordinate bonds with many metals. Iron is the particular metal that is "tuned" with the precise porphyrin and protein structure to make the right "stickiness" to transport the oxygen molecules.

Carbon monoxide poisoning occurs because a carbon monoxide molecule can bond to the haemoglibin in exactly the same place and style as the dioxygen molecule does. But the bond to carbon monoxide is much stronger, and it can be picked up, but will not let go. Any haemoglobin molecule that finds a carbon monoxide molecule is taken out of the oxygen transport system forever, and new haemoglobin must be made by the body to replace it.