Origins of Life LACSSP presentation

1. Origins of Life LACSSP presentation Dr. Bill Nelson, USC Wrigley Institute for Environmental Studies July 23, 2012 Wrigley Marine Science Center

2. First life

3. What is life? Five characteristics of living organisms: Distinct, recognizable organization Reproduction (with wobbly precision) Response to environmental stimuli Internal constancy (homeostasis) Require energy to maintain the other characteristics (they eat)

4. When do we think life started?

5. Earliest fossils of cellular life (3.4K mya)

6. What happened in those 700,000,000 years? Things cool down

7. 700,000,000 years is a long time 7x108 calories is 1.3 million Big Macs 7x108 pennies weigh about the same as 13 blue whales, and stacked up would stretch almost 674 miles. Jupiter is 7x108 miles from the sun.

8. Steps for development of life • Abiotic synthesis of small organic molecules • Joining of these small molecules into macromolecules • Packaging of molecules into “protocells” • Origin of self-replicating molecules

9. Macromolecule formation Small organic molecules polymerize into macromolecules when they are concentrated on hot sand, clay, or rock. RNA monomers have been produced spontaneously from simple molecules Random formation of polymers results in macromolecules that catalyze specific chemical reactions (enzymes) Proteins (chains of amino acids) Catalytic RNA (chains of nucleotides)

10. Units join to make macromolecules Just like Legos™! Polynucleotide synthesis Polypeptide synthesis

11. Enzymes Macromolecules can catalyze chemical reactions Hold reactants close together Localize favorable conditions Proteins and RNA can have catalytic activity

13. Protobionts Small membrane-bounded droplets called liposomes can form when lipids or other organic molecules are added to water Organization Enzymatic activities partitioned from the environment Internal constancy Allows linking of reactions Energy metabolism

14. Relative turbidity, an index of vesicle number 0.4 Precursor molecules plus montmorillonite clay 0.2 Precursor molecules only 0 40 60 0 20 Time (minutes) Self-assembly

15. Take away message Macromolecules can form from the building blocks found in the primordial soup Enzymatic function is an emergent property of macromolecule formation Lipid bubbles can form spontaneously to sequester macromolecules from the environment forming protobionts There was plenty of time for chance to yield function and organization

16. Protobionts to life How did reproduction begin? To understand this, we need to know how it works now.

17. Central Dogma of Molecular Biology Originally espoused by Francis Crick DNA replication reverse transcription transcription RNA replication translation

18. DNA Deoxyribonucleic acid A polymer of 4 bases Adenosine (adenine base + deoxyribose) Thymidine (thymine base) Guanosine (guanine base) Cytidine (cytosine base) Anti-parallel helical structure A pairs with T (2 hydrogen bonds) G pairs with C (3 hydrogen bonds)

21. DNA replication Helix is opened Complementary strand is synthesized Semi-conservative replication

22. Central Dogma of Molecular Biology Originally espoused by Francis Crick DNA replication reverse transcription transcription RNA replication translation

23. RNA Ribonucleic acid (still has its oxys) A polymer of 4 bases Adenosine (adenine base + ribose) Uridine (uracil base) Guanosine (guanine base) Cytidine (cytosine base) Usually single-stranded Less stable than DNA

24. RNA and DNA hold information in the same way

25. Take home message DNA is a polymer of 4 nucleotide bases in an anti-parallel helix The pairing of A:T and G:C means each strand contains the same information DNA replicates in a semi-conservative manner RNA is similar to DNA, and holds information in a similar manner

26. Protobionts to life How did reproduction begin? The first genetic material was probably RNA, not DNA Ribozymes: catalytic RNAs Evidence of ribozymes that can synthesize RNA

27. RNA World Protobionts develop self-replicating RNAs Those RNAs begin to add other genes to themselves Natural selection would result in those that replicate the best and have the most efficient energy metabolism Ta da! Life! At some point DNA replaces RNA as genetic material, probably due to increased stability.

28. Take-away message • We don't know exactly how life started on earth • BUT life appears to be an emergent property of the chemical environment of the early earth. • Experiments have shown that the hypothesized steps necessary for life to have developed from an abiotic primordial soup CAN occur • Formation of macromolecules • Formation of 'protobiont' minicells • Development of reproduction • Low probability events will occur given enough time (and 700,000,000 years is a lot of time) • Life only had to develop once to evolve into the incredible diversity we now observe

29. Fin Note: The following slides are not part of the Original presentation, but are Additional information to support the Presentation.

30. Prebiotic Earth chemistry As proposed by JBS Haldane and AI Oparin (1920s): No free oxygen (i.e. O2) Methane (CH4), ammonia (NH3) Water Free hydrogen (H2)

31. Abiotic production of organic compounds 1952: Stanley Miller & Harold Urey recreated the assumed early atmosphere Contained H2O, H2, CH4, NH3 Lacked free O2 Energy input in forms of heat and electrical sparks

32. Abiotic production of organic compounds After two weeks they detected amino acids (building blocks of proteins) Similar experiments by other scientists demonstrated abiotic production of nucleotide bases (building blocks of DNA), as well as other biologically important chemicals

33. Where did life originate? Scientists now believe the earth’s early atmosphere to have been composed of H2O, CO, CO2, and N2 emitted by volcanoes. Were the key organic molecules formed elsewhere in the early earth? Submerged volcanoes? Mineral-rich deep sea vents?