Everything about The Pah World Hypothesis totally explained
The
PAH world hypothesis is a
biological hypothesis that proposes that the use of
polycyclic aromatic hydrocarbons (PAH) was a means for a pre-
RNA World basis for the
origin of life. As yet it's untested, though in
2007 Cassini spacecraft found the presence of heavy negative
ions of
tholin in the upper regions of
Titan’s atmosphere.
Experiments such as the
Miller experiment and others allow the simple construction of primitive
organic molecules including
amino acids. The
RNA world hypothesis shows how RNA can become its own
catalyst (a
ribozyme), and so become the basis for evolution of life. In between there are some missing steps such as how the first
RNA molecules could be formed. The PAH world hypothesis was proposed by Simon Nicholas Platts in
2005.
It is known that polycyclic aromatic hydrocarbons are a likely constituent of the
primordial sea. PAH's are not normally very soluble in sea water, but when subject to ionizing radiation such as solar
UV light, the outer
hydrogen atoms can be stripped off and replaced with a
hydroxyl group, rendering the PAH's far more soluble in water.
PAHs are
amphiphilic, which means that they've parts that are both
hydrophilic and
hydrophobic. Thus when in solution, like
lipids, they tend to self organise themselves in stacks, with the hydrophobic parts protected.
In this self ordering stack, the separation between rings is 0.34 nm. This is the same separation found in RNA and
DNA. Smaller molecules will naturally attach themselves to the PAH rings. However PAH rings, while forming, tend to swivel around on one another, which will tend to dislodge attached compounds that would collide with those attached to those above and below. Therefore it encourages preferential attachment of flat molecules such as
pyrimidine and
purine bases. These bases are similarly amphiphilic and so also tend to line up in similar stacks. This ends up making an effective scaffold for a
nucleic acid backbone to form along the bases.
A small change in acidity would then allow the bases to break off from the original stack of PAHs and so form molecules like RNA.
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