The Origin of Life

1. The Origin of Life Oparin’s Heterotroph Hypothesis + MORE!!!!!

2. It is widely held that the sun and planets in our solar system were formed ~4 ½ to 5 B years ago from a cloud of cosmic dust & gas The Earth was originally a “hellish” place So where did the building blocks of life come from? A meteor? What? The present atmosphere = oxidizing; Primitive atmosphere = reducing Oxidizing: chemical reactions due to oxygen; 21% oxygen and 78% nitrogen

3. Objectives: Discuss various hypotheses on the Origin of Life on Earth Explain Oparin’s Heterotroph Hypothesis and how Miller and Urey’s experiments supported this hypothesis Sequence the events that might have led to the evolution of complex molecules and the first organisms. Bubble Theories Compare Prokaryotic Cells (archaebacteria and eubacteria) to Eukaryotic Cells (plant and animal cells among others)

4. Origin of Life Hypotheses Special creation supernatural or divine origin Extraterrestrial origin panspermia Spontaneous origin life originated from inanimate materials

5. Reducing Atmosphere The primitive atmosphere was not conducive to life Energy sources such as UV rays, gamma rays, lightening, radiation from the earth were much greater than today Early atmosphere is often referred to as a reducing atmosphere. exact conditions unknown Oparin thought that there was methane (CH4), water vapor (H2O), Hydrogen gas (H2), and ammonia (NH4) ample availability of hydrogen, carbon, oxygen and nitrogen atoms very little free oxygen (O2) If free oxygen had been there- life would not have evolved As energy hit the molecules in the early atmosphere bonds broke and new ones were made. The ocean became a “hot thin soup” filled with organic molecules.

6. Schema of the Bubble Hypothesis

7. Miller-Urey Experiment

8. Miller-Urey Experiment Attempted to reproduce early reducing atmosphere and produce organic compounds from inorganic materials Tested Oparin’s hypothesis (chemical evolution) Materials hydrogen-rich atmosphere electrical discharge Succeeded in producing amino acids, urea, lactic acid, (and nucleotides if phosphorous was added)

9. Sidney Fox heated amino acids at high temperatures in salt water and found aggregates of large protein growing and budding off to make more. • Oparin called these Coacervates. • The protein complexes surrounded themselves with a watery shell which allowed the inside to differ from the outside environment • As coacervates became more complex they may have developed biochemical systems with the capacity to release energy from organic nutrients in the “Hot Thin Soup”. (the early ocean with all those organic molecules) • The first cells were heterotrophs according to Oparin.

10. Current Theories on the Origin of Life - Location- Ocean’s edge- with volcanoes Oparin’s bubble hypothesis/ coacervate theory /primordial soup/ chemical evolution Under frozen seas problematic due to necessary conditions Deep in Earth’s crust byproduct of volcanic activity Within clay positively-charged clay Deep-sea vents conditions suitable for Archaea

12. Earliest Cells Ongoing debate concerning actual path/ start-off point for cell evolution Microfossils have been found in rocks as old as 3.5 billion years old. resembleprokaryotes lack nucleus of more complex eukaryotes PROKARYOTE Pro: before; Karyon: nucleus Genetic material not bounded by a nuclear membrane; no membrane-bound organelles The earliest heterotrophic prokaryotes gave off CO2 as they ANAEROBICLY RESPIRED!!! A new Gas!!! As the number of heterotrophs grew, they ate up the “soup”! As the CO2 amount grew in the atmosphere, eventually organism may have evolved that could use CO2 and H2O to make sugars These organisms were anaerobic autotrophs and they gave off OXYGEN to the atmosphere!!!! A new Gas!!!! With O2 in the environment, aerobes could evolve!!!!

14. Prokaryotes: Archaebacteria extreme-condition prokaryotes lack peptidoglycan in cell walls Methanogens (produce methane CH3) extreme halophiles (salt-loving) extreme thermophiles (heat-loving) thought to have split from Bacteria 2 bya.

15. Prokaryotes: Eubacteria- true bacteria second major group of prokaryotes strong cell walls simpler gene structure contains most modern prokaryotes includes photosynthetic bacteria (cyanobacteria) Pathogenic & non-pathogenic

16. First Eukaryotic Cells EUKARYOTE Eu: true; Karyon: nucleus Genetic material within nuclear membrane; w/ membrane-bound organelles Eukaryotes probably arose about 1.5 bya. Internal membrane-bound structures such as mitochondria and chloroplasts are thought to have evolved via endosymbiosis. Energy-producing bacteria were engulfed by larger bacteria. beneficial symbiotic relationship

17. Endosymbiosis

18. First Eukaryotic Cells Sexual reproduction Eukaryotic cells can reproduce sexually, thus allowing for genetic recombination. Genetic variation is the raw material necessary for evolution. Multicellularity arisen many times among eukaryotes fosters specialization (ex. Tissues) After a buildup of oxygen, ozone formed which blocked the harmful rays of the sun so life could come onto land.

19. Extraterrestrial Life Universe has 1020 stars similar to our sun. Conditions may be such that life has evolved on other worlds in addition to our own. Ancient bacteria on Mars. Largest moon of Jupiter, Europa, covered with ice. liquid water may be underneath What do you think? Hmmm… Image Credit Comet Hale-Bopp 1997