dvunkannon
Posts: 1377
Joined: June 2008
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Driving to work today, I was thinking about vesicle division - what would drive the splitting of a big vesicle into two small ones. By vesicles here, I'm considering the protocells of some chemistry bounded by a lipid bi-layer, such as is mooted as an early step in OOL.
First, it wasn't obvious to me why a vesicle would ever split at all. Why not keep growing?
The first process I thought of was something that would expel a good amount of the volume of the vesicle while leaving the lipid surface intact. As volume goes down, splitting into two spheres makes energetic sense. Perhaps some regulatory circuit detects that the interior of the vesicle is getting too watery, and in response water is pushed out.
It might work, but I didn't think it was too realistic. When bacteria divide, do the daughter cells have significantly less volume than the parent?
So my second idea was simply that the vesicle produces too much of the lipid 'skin' in relation to its rate of production of the vesicle contents. Assume there is a primitive genome that codes for proteins that build lipids or are vesicle contents. In the genome, there is a fixed ratio of lipid to content protein genes. But as the vesicle grows, it needs less and less skin for a given amount of content (cube/square law in action). If the vesicle continues to produce lipids and contents in arithmetic rather than geometric ratio, it will be making too much skin. At some point, the best use of all that skin is to invaginate and split.
I like this second explanation because it is very simple and mechanical in nature. The vesicle is just minimizing the energy of the physical system when it splits, no fancy awareness of accumulating resources hitting some magic level that says "it is now safe to split."
Comments? I have no idea if this is already a commonplace idea.
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I’m referring to evolution, not changes in allele frequencies. - Cornelius Hunter
I’m not an evolutionist, I’m a change in allele frequentist! - Nakashima
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