NINE

Emergent Life II

A Proposed Origin Of Life On Earth:

from protobionts to living cells

adapted from Biology, 2015, tenth edition, pp. 439-446

the pre-cell

an internal energy source is

coupled to

chemical reactions

between

simple molecules,

enclosed within

 a boundary,

to form a

self-sustaining,

increasingly

organizing

system

that must

grow

and

reproduce

AN RNA WORLD:

"...the first informational molecule to evolve in the progression toward a self-sustaining, self-reproducing cell...proteins and DNA...came...later...[is] self-replicating RNA molecules...[that] functioned as both enzymes and substrates for their own replication...", eventually catalyzing and facilitating peptide bond formation, and also eventually making double-stranded copies of itself (i.e., DNA) (Biology 2015, 10th edition, p. 442, 443).

vesicle-like assemblages

of organic polymers

promote the development of:

1) surface membranes of fatty acids and monoglycerides,

surrounding larger DNA-like molecules;

2) small, organic molecules, or nutrients, that can enter (diffuse) through the cell membrane; 

3)  larger DNA molecules that cannot leave the cell; and,

4) DNA, that with its double helix structure, is more stable/less reactive, than RNA.