Chapter 19-1 ~ Origin and History of Life

Close your eyes and imagine our

planet 4 billion years ago… what do you see? How is it different from

today?

Early history of life

Solar system~ 12-10 billion years ago (bya)

Earth~ 4.6 bya Life~ 3.5 to 4.0 bya Prokaryotes~ 3.5 to 2.0 bya

stromatolites Oxygen accumulation~ 2.7 bya

photosynthetic cyanobacteria Eukaryotic life~ 2.1 bya Muticelluar eukaryotes~ 1.2

bya Animal diversity~ 543 mya Land colonization~ 500 mya

Interesting facts about the origins of life

There is more metabolic diversity among the two kingdoms of prokaryotes then all the eukaryotes combined

Bacteria separated from Achaea bacteria early on in the history of life ~2 to 3 B.Y.A.

Fungi are more closely related to animals than they are to plants

Fungi and plants worked together to symbiotically colonize land… which happened fairly recently on the geologic time scale…. 475 million years ago

Evidence of early life

Stromatolites are fossilized layers of sediment formed from the migration of bacteria upward

Early fossils

The Origin of Life Spontaneous generation

vs. biogenesis (Pasteur) The 4-stage Origin of life

Hypothesis: 1- Abiotic synthesis of

organic monomers 2- Polymer formation 3- Origin of Self-

replicating molecules 4- Molecule packaging

(“protobionts”)

Origin of Life

Organic monomers/polymer synthesis Abiotic Synthesis Model Oparin /Haldane (1920)

working independently hypothesized that simple monomers (monosaccharides, amino acids, and nucleotides) could be synthesized from inorganic molecules in the early atmosphere in the presence of volcanic vapors (reducing atmosphere) with lightning , UV radiation and no Oxygen.

Early atmosphere probably consisted of Water vapor, N2, and CO2 with small amounts of hydrogen gas (H2), methane (CH4), ammonia (NH3), hydrogen sulfide (H2S) and carbon monoxide (CO).

Testing the abiotic synthesis hypothesis

Miller/Urey (1953) experiment: Placed a mixture resembling a strongly reducing

atmosphere of water , hydrogen gas (H2), methane (CH4), and ammonia (NH3)… heated it and circulated it past an electric spark for a week.

Results: A variety of amino acids, nitrogen bases, & ATP formed

Criticism of the Miller/Urey experiment Placed ammonia (NH3) in the mixture… not a major

component of the early atmosphere… (N2) was plentiful but inert unlike ammonia

Where was ammonia being synthesized in large amounts on primitive earth?

Oparin /Haldane hypothesis was modified to include iron-nickel sulfides produced in the extreme heat of hydrothermal vents that act as catalysts for froming both ammonia, amino acids, and even peptide chains!

Polymers Evolve Fox amino acids can polymerize forming

proteinoids, small polypeptides with some catalytic capabilities, from organic monomers dripped on hot sand, clay or rock. Fox also demonstrated in laboratory the formation of microspheres, small cell like structure consisting only of protein, from the coagulation of proteinoids.

Fox proposed the “Protein First Hypothesis” and stated that protein enzymes came before the genes that code for proteins.

This is supported also by the fact that DNA replication is highly dependent upon many protein enzymes.

Polymers Evolve Cairns-Smith Polypeptides and RNA Nucleotides

came to be at the same time on a warm bed of clay that consisted of iron and zinc catalysts. Cairns-Smith envisioned the RNA directing the polypeptides to replicate more RNA which would code for more polypeptides.

Cech/Altman RNA first hypothesis… RNA was both the substrate and the enzyme (acting like a polypeptide/protein) creating a world in which all the genes were RNA and not DNA.

Protocells or Protobionts…not quite a cell but it is a start… It has a

membrane

Provides a safe place for chemical reactions to occur!

A simple heterotrophic protocell could have contained RNA acting as a gene and an enzyme…Some simple form of Glycolysis may have been occurring to produce an ATP like molecule for energy

RNA the Origin of Life

Evolution of the Cell

The origin of heredity information made Darwinian evolution possible

Once a membrane formed around the RNA that was producing protein, now there was a selective advantage and the inheritance was possible

RNA eventually gave way to the more stable DNA… the “RNA World” gave way to the “DNA World”!

Panspermia

The idea that Earth was seeded from life from outer space

Amino acids are found in some meteors that strike our planet today

Early Earth was bombarded constantly with meteors

Is life restricted to Earth… What is your opinion?