1. Origin Of Life Earth formed 4.6 billion years ago Life ~ 3.5 billion years ago What was the primitive environment of Earth like? –Reducing (electron adding) atmosphere –No electron hogging oxygen gas was present –“Primordial Soup” just waiting for lightning…

2. Life…. Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages: 1. Abiotic synthesis of small organic molecules 2. Joining of these small molecules into polymers 3. Packaging of molecules into “protobionts” 4. Origin of self-replicating molecules

3. Step One: Chemical Evolution Oparin and Haldane: –Separate theories about early Earth –Reducing atmosphere + high energy levels contributed to spontaneous chemical evolution Miller & Urey (1953, U of C) tested hypothesisMiller & Urey (1953, U of C) tested hypothesis First organic compounds may have been synthesized near submerged volcanoes and deep-sea vents deep-sea vents

4. Other theories Some organic compounds may have come from space –Carbon compounds have been found in some meteorites that landed on Earth Small organic molecules polymerize when concentrated on hot sand, clay, or rock (Sidney Fox – Protenoids, microspheres)

5. Protobionts Aggregates of abiotically produced molecules surrounded by membrane/membrane-like structure Experiments demonstrate that protobionts could have formed spontaneously Liposomes –small membrane-bounded droplets that can form when lipids/other org molec added to water –Grow and appear to split “give birth”

6. Protobionts Maintain different internal environment Microspheres – selectively permeable protein membrane –Display osmotic swelling –Stores energy –Has a membrane potential

7. Polypeptide, nucleic acid, and polysaccharide aggregates –Hydrophobic macromolecules surrounded by shell of water molecules –Can absorb substrates –Release products –May have enzymes associated with them Coacervates

8. What’s Missing? In chemical evolution the environment selects for best suited molecules to survive What ingredient necessary for life is missing in all protobionts? No hereditary material that would ensure continuity!

9. Which Came First RNA or DNA? RNA! RNA has the following properties: –Less complex than DNA –Less stable than DNA –Short strands of RNA can replicateShort strands of RNA can replicate –Ribozymes (RNA molecules) - show enzymes can be non-protein molecules

10. Experiments have proven that RNA can evolve The RNA world was slowly able to direct protein synthesis and preserve and copy the genetic informationThe RNA world was slowly able to direct protein synthesis and preserve and copy the genetic information As evolution continued different early cells showed varying success with life One trend resulted in DNA as the ultimate hereditary material RNA world  DNA world!

11. Early Life Prokaryotes – only life (3.5 ~ 2 bya) Electron transport systems essential to early life Earliest types of photosynthesis did NOT produce O 2 Oxygenic photosynthesis ~ 3.5 bya in cyanobacteria

12. Land plants Animals Paleozoic Meso- zoic Ceno- zoic Origin of solar system and Earth Multicellular eukaryotes Single-celled eukaryotes Prokaryotes Atmospheric oxygen Proterozoic Eon Archaean Eon Humans Billions of years ago 41 23

13. Endosymbiotic Theory How did eukaryotes evolve from prokaryotes? Oldest eukaryotic cell fossils ~ 2.1 bya Endosymbiosis theory –mitochondria & plastids were formerly small prokaryotes living within larger host cells Prok ancestors of mitochondria/plastids gained entry to host cell as undigested prey/parasites In the process of becoming more interdependent, the host and endosymbionts would have become a single organism

14. Plasma membrane Cytoplasm DNA Ancestral prokaryote Endoplasmic reticulum Nuclear envelope Infolding of plasma membrane Engulfing of aerobic heterotrophic prokaryote Nucleus Cell with nucleus and endomembrane system Engulfing of photosynthetic prokaryote in some cells Mitochondrion Ancestral heterotrophic eukaryote Ancestral photosynthetic eukaryote Mitochondrion Plastid

15. Earliest Multicellular Eukaryotes Molec clocks – earliest common ancestor of multi euk ~ 1.5 bya (oldest fossils – 1.2 bya) The first multicellular organisms were colonies, collections of autonomously replicating cells

16. “Cambrian Explosion” Most of the major phyla of animals appear in the fossil record of the first 20 million years of the Cambrian period

23. In this format the RNA would be shared by all competing RNA molecules

25. Shows molecules smaller than RNA can self-replicate!