Hemoglobin and chlorophyll

[snopes]

Comment: I read that, from a molecular standpoint, the only difference
between chlorophyll and human blood is in the center atom. In human blood,
the center atom is iron, and in chlorophyll, it is magnesium. Is this
true?

[snopes]

Hemoglobin:



Chlorophyll:

[Alarm]

So what's the answer then?

[Gin Rickey]

I know next to nothing about chemistry, but even if that were true (that the only difference is the atom at the center) that would still be quite a substantial difference, no?

[snopes]

Originally Posted by Alarm

So what's the answer then?

They're similar but (aside from the center atom) not identical:

http://alliedhealthblog.com/2010/11/...nd-hemoglobin/

[Jahungo]

Nitpick: that's heme, not hemoglobin. Hemoglobin is a complex of the heme group and the much larger globin protein.

ETA: There's also the name for the general structure: a porphyrin ring.

ETA2: Even more biochemistry fun - both are derived from the same precursor, protoporphyrin IX, as shown in this pathway diagram.
Here's it's structure for comparison.


Isn't biochemistry fun!

[A Turtle Named Mack]

Originally Posted by Gin Rickey

I know next to nothing about chemistry, but even if that were true (that the only difference is the atom at the center) that would still be quite a substantial difference, no?

Maybe, maybe not. In most organic molecules, the side groups from the main chains and rings are what makes the biggest difference. If there is an atom of something besides the usual culprits (C, O, H, N, S: I think those are the regulars), then it might just be a sort of placeholder. OTOH, the odd atom's electronegativity (attraction for charged particles) can make a subtle but crucial difference in the way it reacts. For instance since hemoglobin needs to be able to both hold onto and release O2 and CO2, you can imagine that the difference between an iron atom and some other metal might be critical. Of course, if animals had started using copper for some reason, then the structure of the hemoglobin-function molecule would probably have evolved differently to be efficient with a copper in it, rather than an iron. Then we could be Vulcans.

[Nick Theodorakis]

Originally Posted by A Turtle Named Mack

... Of course, if animals had started using copper for some reason, then the structure of the hemoglobin-function molecule would probably have evolved differently to be efficient with a copper in it, rather than an iron. Then we could be Vulcans.

Actually, the oxygen carrier used in many invertebrate animals is hemocyanin, which is a copper metalloprotein (although not a hemoprotein).

Nick

[jimmy101_again]

While hemoglobin binds both molecular oxygen and carbon dioxide the heme group (see Jahungo's post) just binds the molecular oxygen. The carbon dioxide binding site is not at the heme.

The proteins that hold the heme and chlorophyll are a fair bit different and contribute pretty significantly to the different activities.

[Nick Theodorakis]

Although carbon monoxide does bind to the heme, and in fact more strongly than oxygen does, which is why it's so dangerous.

Nick

[Troberg]

Well, they are not the same, even if that central atom is ignored, but they are clearly related. One can't help but wonder what would happen if one was to replace the central atom in chlorophyll and try to replace hemoglobin with the "hemophyll". Or, for that matter, doing the opposite and try to replace chlorophyll with "chloroglobin".

It sure would be some nice science.

Perhaps we'd turn green in the sun instead of getting a tan?