« Protists in Wonderland | Main | The Perfect Pitch »


Paul Orwin

I wish I had something really smart to say about this! A hugely interesting question to me, but one I'm utterly unqualified to even start answering.

Still, that never stops me...I think one issue to confront is the difficulty of the LUCA idea, and how it intersects with the world that was. When I think about this, it helps me to think about "mitochondrial eve", and the notion that everyone on earth has a common ancestor x kya (not sure what x is, maybe 40-50?). This obviously doesn't mean that there was just one person - a banal statement that bears on our more interesting discussion! The Universal Common Ancestor doesn't need to have been a monoculture! There may be many things that lived that do not have living progeny in the current world (that we know of...). So, this leaves us with the interesting question of just how weird they might have been.

Returning to the question at hand. I have always been baffled by the seeming paradox of different lipids between Eubacteria/Eukarya on one side and Archaea on the other, combined with closer relationships at the gene expression level between eukarya and archaea. It seems to me easier to believe that there might have been a period of time where lipid bilayers were produced containing both types of linkages? I'm not a biochemist, so maybe these would be unstable for some reason I don't know, but it doesn't seem like a big problem. So, if the LUCA had both types of linkage, it could then have lost one or the other.

So I guess I come down in favor of III. We can't use differential loss to explain all the differences, because it is much harder to envision having two extensive, complex, and separate systems for controlling transcription, but much easier to envision lipid synthesis genes with redundancy.

It also seems to me that the archaeal membrane might have added stability compared to the eubact/eukaryote membrane because of it's chemistry (again, not a biochemist!). So organisms with either machinery might have been at a disadvantage to an organism with both phospholipid types in certain environments. Also, we assume based on current single celled organisms that carrying extra DNA is a fitness burden, but maybe it wasn't back then? If we assume that LUCA had Archaeal lipids and Eubacterial lipids, and Archaeal txn machinery, we still have to figure out where Eubacterial txn came from. I've got no idea! I'll have to read that paper before I comment further, though!

Verify your Comment

Previewing your Comment

This is only a preview. Your comment has not yet been posted.

Your comment could not be posted. Error type:
Your comment has been saved. Comments are moderated and will not appear until approved by the author. Post another comment

The letters and numbers you entered did not match the image. Please try again.

As a final step before posting your comment, enter the letters and numbers you see in the image below. This prevents automated programs from posting comments.

Having trouble reading this image? View an alternate.


Post a comment

Comments are moderated, and will not appear until the author has approved them.

Your Information

(Name is required. Email address will not be displayed with the comment.)