Unit 3:  The origin and evolution of life                          1   2   3   4   5   6 

1.3. The protobiological evolution

The macromolecules association to form the first cells is the most controversial and unknown point.

It is supposed that the process involved several events which led to the formation of the first protobiont. The minimum elements to form a protobiont are:

- Membrane (an envelopment that include macromolecules inside)

- Metabolism (chemical reactions performed by enzymes)

- Self-replication (reproduction and transmission of inheritance information)

a) Vesicles

- Coacervates 

Oparín proposed that within the prebiotic soup, little spheres (coacervates) were formed. In their interior, they trapped other macromolecules, as enzymes able to perform chemicals reactions (metabolism). These coacervates were the early protobionts.

- Microspheres

It is a similar hypothesis suggested by Fox. In this case the spheres were made of proteins.

- Liposomes

They are little spheres of phospholipids that form spontaneously when these fats are placed in water. Current cells have lipidic membranes.

b) Self-replication

- Gen origin (RNA world hypothesis)

This hypothesis was proposed by Condie and Sloan in 1998. Before the appearing of the protobionts (coacervates and protein microspheres) appeared some molecules able to replicate themselves (ribozimes). They can be considered the first carriers of genetic information.

Probably the first molecule which contained genetic information was a RNA that in addition was able to replicate itself. In a posterior phase of evolution, the role to carry inheritance information passed to DNA, a more stable molecule, and the catalytic role passed to proteins (enzymes). 

1.7. What is “the RNA world”?

1.8. Which are the minimum building blocks to make a protobiont?