Question

Compare and contrast the RNA World hypothesis to the Iron/Sulfur World hypothesis regarding the origins of early protocells. Make sure to list the strengths and weaknesses of each.

Answer 1

RNA world hypothesis states that the first life forms were self-replicating RNA. This RNA molecule have catalytic and information carrying capacity have catalyzed or acted as a template for RNA synthesis.

• Gene first model for the emergence of life.
• The hypothesis suggests that short RNA molecules could have spontaneously formed and are capable of catalyzing their own continuing replication.
• Theory suggest that life began in a cold prebiotic broth of monomers with de novo emergence of replicating RNA as functionally self-contained polymer.
• Suggest that life emerge heterotrophically in an aqueous environment.
• Subsequent evolution is characterized by RNA are DNA memory takeover and ribozyme catalyst takeover.
• According to the RNA World theory the process of early evolution is genetic and stochastic from the start.
• Self-organization explanation is not accurate in this theory so not useful for progressive research program.

Problems with RNA world hypothesis is that:

• the instability of RNA when exposed to ultraviolet light
• the difficulty of activating and ligating nucleotides,
• the lack of available phosphate in solution required to constitute the backbone of nucleotide,
• the instability of the base cytosine (which is prone to hydrolysis)
• the hypothesis have incomplete evidence supporting them

Recent experiments suggest that the original estimates of the size of an RNA molecule capable of self-replication are probably underestimates.

Iron/Sulfur World hypothesis proposes that early life may have formed on the surface of iron sulfide minerals.

• Metabolism first model for the emergence of life.
• The FeS World theory also states that life began as an autotrophic metabolism in hydrothermal fluids of hot volcanoes.
• Suggests that life begin autotrophically as a 2-dimensional organic monolayer on the surface of a mineral at a hydrothermal submarine location where, oxidation of mackinawite to pyrite occurs and it provides energy for the fixation of gaseous carbon and primitive metabolic reactions on the pyrite surface.
• Hypothesis well explained the potential for hydrothermal systems to promote organic synthesis.
• According to the FeS World theory the overall process of early evolution has two tracks: (i) Primary track is a chemically pre-determined process. It begins with a set of catalytic transition metals, nutrients and synthetic carbon fixation reactions to generate small organic ligands ( act as catalyst for further evolutionary reactions). (ii)Secondary track is a genetic process. It begins with modified polynucleotide sequences which are then translated into new peptides and these new peptides become ligands. This secondary genetic track is stochastic and requires mutations and selection.