[extropy-chat] Lipid bilayer constraints and considerations -- Was Cryonics is the only option?

[Brett Paatsch]

Anders wrote:

> Now, our big disagreement really seems to be the constructability of 
> bilayers. I say they probably can be put together according to fairly
> complex specifications by working a LN temperatures and then 
> thawing, you say it cannot be done. Maybe we should start a separate
> thread to actually hash it out freshly, stating assumptions and all that?

[ this paper seems relevant, but I haven't found the full text yet:
http://journals.cambridge.org/action/displayAbstract;jsessionid=2DB1538444172C5407EB5A708E22DA6E.tomcat1?fromPage=online&aid=365124
]

Okay. Sure. The relevant bilayers for cells, that are functional as cells, are
not flat ones like sheets of fat floating on water, they are volume containing 
3D ones like balloons of different shapes and sizes that separate what is 
inside from what is outside them. They can be as thin as 6 nm. In neurons
the bilayers, like a skin, have an arboreal shape of the interleaving neurons
themselves and may extend in individual neurons extend unbroken from the
axon to dendrite tips which may be separated by distances as much as a
metre.  

These bilayers are found for instance in the plasma membrane that is 
around the cell overall around mitochondria where the bilayers are crucial
to the functioning of the hydrogen ion pumping of the mitochondria, in the
ER and the nucleus, in the golgi, and in lysosomes etc and, rupturing 
these bilayers is often going to be fatal to the cell. Vesicles also have
bilayers. 

The human brain has a volume on average of 1450 millilitres or cubic
centimetres. (figure 1 associated email attachment) This volume is 
approximately equivalent to that of a cube with sides of 11.318512 cm
or  113,185,120 nanometres.(fig 2) 

Assume 50 nanometre cubic volumes are sufficient for requisite level
of molecular detail. (fig 4)  

This means that the human brain could be conceptualised as 
comprising about 1.45 10^24 such cubic volumes. 1.45 trillion trillion
cubes.

Lipid bilayers will be disperse throughout those cubes not necessarily
evenly and of course without particular structures like filopodia falling
neatly into those 50 nm volumes.

If the 50 nm cubes can be put together using a manufacturing process
and attached to each other such that the lipid bilayers fuse and their
contents are not spilled then you'd have a successful reconstruction
of the biological brain. 

But I say, it can't be done. The physics and chemistry of the biomolecules
won't allow it to be done as a manufacturing process. 

Anders you say it can? Then let's see how. 


- Brett Paatsch

PS: Apologies for the very rough sketches. 

For simplicity I'm assuming a filopodia containing a single actin "strut"
is the finest scale of bilayer-enclosed structure than formed by cells
in the brain.  I'm assuming that you need to be able to restore to brain
to the filopodial scale.  

Late last year I asked a Melbourne University neuroscientist and 
lecturer in the school of anatomy and cell biology what level of 
detail would be needed to accurately pick up the structural
information of the brain - he said 50 nm. 

I think 50 nm seems reasonable based on two lipid bilayers of
6 nm each, 1 actin strut of 5-9 nm, some space around the
strut for assembling it say 12nm and build into the lipid 
bilayer are molecules such as integrins which bind cadherins
and the extracellular matix, as well as other proteins and
sugars getting to around 50 nm in cross section.  

Sizes of structures taken from Alberts Molecular Biology
of the Cell 4th Edition 2002 available at the NCBI bookshelf. 

 




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