Lecture 4: The Origin of Life

rutgers genbio

abiogenesis

first life developed from non-living organic molecules

abiotic synthesis

molecules had to form spontaneously

prebiotic soup hypothesis

life formed near Earth’s surface—spontaneous formation of monomers

who suggested prebiotic soup hypothesis?

Oparin and J.B.S. Haldane

iron-sulfur world hypothesis

life formed at cracks of ocean floor, leading to hydrothermal events: hot water and carbon monoxide (and minerals) were released and iron was a catalyst to build molecules

requirements for abiotic synthesis

little to no free oxygen, source of energy, CHON, and time for molecules to react with one another

why does abiotic synthesis require little to no oxygen?

oxygen breaks bonds (oxidizes)

formation of organic macromolecules

formation of polymers from monomers (protein or RNA)

where do monomers polymerize?

hot sand or rock

what catalyzes polymerization?

metal ions (Zn⁺², Fe⁺²)

formation of protocells

lipids spontaneously form vesicles, organic polymers exhibit attributes of living cells (osmosis, homeostasis, divide), and no mechanism of heredity

vesicle

container

protocells

aggregates of abiotically produced organic macromolecules; exhibit attributes of living cells (electrical potential across surface, absorb materials → osmotic swelling, unique internal chemical environment, divide if sufficiently large); no mechanism of heredity

nucleic acid in protocells

RNA

ribozymes

capable of self-replication and catalyze protein synthesis

catalyze

lower the energy needed to start a reaction

RNA-peptide world hypothesis

the first replicating systems used RNA to store and copy genetic information; limited role for polypeptides and DNA was incorporated later

when did the first prokaryotes form?

3.5 billion years ago

was there a lot of O₂ in early life?

no—there was not much, and it was all heterotrophic bacteria

first heterotrophs

anaerobic, used fermentation

autotrophy

later, photosynthetic autotrophs appear (cyanobacteria) and use energy from sunlight and release O₂, leading to a rise of O₂ and the Oxygen Apocalypse

oxygen apocalypse 

about 2.5 billion years ago, there was a rise in atmospheric O₂ due to oxygenic photosynthesis; this killed off most organisms and banded iron formation

eukaryotes

eukarya arise from archaea and bacteria; symbiotic relationship; endosymbiont theory