Primordial Soup in the Kitchen of Life: The Origin of Life

1. Primordial Soup in the Kitchen of Life: The Origin of Life

2. How Do We Classify Life ?

3. Three Domains Archaea Eukarya Bacteria

4. Revised to:

5. And Viruses ?

6. And nanobacteria ? Nanobes growing on clay ? Note: Nanobacteria about 1,000 x smaller than “regular” bacteria disagreement lies in whether or not nanobes are Too small to contain genetic material

7. Recall: Evolution of Earth’s Atmosphere • Initial atmosphere much like Jupiter • (rich in Hydrogen and Helium derived from solar nebula) • -burned off by Solar Wind / escaped weak gravitational field • 2. Second atmosphere much like Venus • (dominated by carbon dioxide from Earth’s interior) • -“The Big Burp” • 3. Third and present atmosphere • (rich in oxygen) • -modified from second atmosphere due to rise of anaerobic, • photosynthesizing organisms

8. Some Basic Characteristics of Living Things • Metabolism: Living things harvest energy from environment, use energy to build, maintain their bodies. • Regulation: Living things have a complex, integrated system that controls conditions within their bodies. • Replication: Living things can produce offspring. • Response to external stimuli: Living things respond to conditions of their external environment as individuals and larger populations.

9. Basic Stages Envisaged In The Development of Life Raw Ingredients Monomers Polymers Cell Membrane Reproduction Living Cell

10. Raw Ingredients Monomers Polymers Cell Membrane Reproduction Living Cell Raw ingredients assumed to have been present in atmosphere and hydrosphere of Early Earth: water carbon dioxide carbon monoxide N-gases S-gases methane ?

11. Raw Ingredients Monomers Polymers Cell Membrane Reproduction Living Cell Monomers demonstrated to be capable of forming abiotically in Miller experiment (and variants) gas mixture including water, methane, ammonia, hydrogen + energy yields: amino acids, sugars, nucleic acid bases, lipids

12. Miller-Urey Experiment (Spontaneous Generation)

13. Products of Miller-Urey Experiments (1953-59) Most important: Amino acids (building blocks of proteins) (alanine, glycine) Ponnamperuma et al (1963) - used high energy electrons on a mixture of methane, water and ammonia - adenine, ribose and deoxyribose synthesised abiotically. Problem: Ingredients used not concentrated in volcanic emissions (therefore probably not in early atmosphere either)

14. Raw Ingredients Monomers Polymers Cell Membrane Reproduction Living Cell • Polymers assumed to form through • concentration, dehydration of monomers • through: • Evaporation of solution near hot springs • Freezing and concentration of solution in cold environments • Adsorption onto charged mineral surfaces

15. Areas where monomers could be concentrated Deep sea vents ? Hot springs ?

16. Ponds in Cold areas ?

17. Polymerization of Simple Organic Molecules By Mineral Templates ? Clay minerals Feldspar

18. Big Problem: Polymerization to Form Genetic Material

19. Raw Ingredients Monomers Polymers Cell Membrane Reproduction Living Cell Cell membrane was required to form the first isolated cell (to contain the necessary complex molecules). Lipids can spontaneously form liposomes (hollow spheres of lipids) . Also, proteins will form microspheres when dehydrated and agitated. Important Properties of these tiny spheres: 1. Maintain separate stable phases in water 2. Membrane maintains electric, pH and redox gradients.

20. Coacervates: Cell Wall ? Can be produced from amino acids (like oil in salad dressing)

21. Raw Ingredients Monomers Polymers Proto-Cell Reproduction Living Cell Advent of Reproduction very problematic in abiogenic models. Main Problem: Chicken and Egg

22. CHICKEN-EGG PROBLEM Synthesis and replication of RNA today happens with help of enzymes (proteins). Proteins are synthesized using coded information in RNA or DNA RNA proteins

23. RNA World (The Naked Gene) • RNA can function as both: • “information” molecules • that can be replicated • and • 2. catalysts (like protein enzymes) • as ribozymes

24. Rationale of Naked Gene Hypothesis: 1. Earliest life form was an energy-harvesting RNA molecule that could catalyze its own replication. 2. The RNA molecules most efficient at energy harvesting and protecting themselves from environmental changes would win over less effective individuals. 3. Natural selection would build complex metabolic and regulation systems incorporating protein enzymes. 4. RNA that could replicate in double-stranded form would proliferate since these forms would have two copies of each code, allowing better detection of “errors” in code

25. Making genetic material abiotically isn’t impossible, but it ain’t walk in the park either Problems: 1. RNA, DNA very complex molecules 2. Need high concentrations of “building blocks” to concentrate and polymerize. 3. Replication of RNA a TWO STEP process Single strand of RNA present, each of its links attract complimentary link (mirror image) out of “prebiotic soup” like making a zipper from one side as template for the other Process would have to be repeated using new “mirror image” to duplicate original side (requires enzymes).

26. Did replication start from proteins ? (Scenario by Sydney Fox) • Imagine: • Sheltered lagoons filled with tiny proteinoid microspheres. • 2. Protenoids catalyze chemical reactions and form outer surfaces acting like cell membranes. • Nucleic acids (DNA, RNA) formed on proteinoid enzyme templates. • 4. DNA (or RNA) “evolve” to function as replicator molecules. • Splitting and fusion of microspheres with exchange of material

27. Another Approach: The Clay Critter Revisited • Properties of mineral crystals: • The result of atoms naturally organizing themselves • Organization at micro- and macro- scale • Clay minerals electrostatically charged, grow by adding • layers to themselves (like pages in a book). • 4. When broken, the fragments can continue to grow • on their own (abiotic “reproduction”).

28. Clay Critter Scenario • Growing clay crystals compete with each other for resources as they grow. • 2. Crystals break apart, be transported in new area where they continue to grow and fragment again; in effect, the world is populated with competing “clay beings.” • 3. Genetic code in effect, charged mineral surfaces. • 3. Eventually, clay critters begin to adsorb and incorporate carbon based molecules to apparatus (e.g. proteins). • 4. Synthesis of DNA or RNA to augment and ultimately replace clay-based “genes.”

29. Panspermia Hypothesis (Earth’s Life Originated Elsewhere) “Fossils” from ALH84001 KINDA COOL, BUT DODGES THE FUNDAMENTAL QUESTIONS

30. END OF LECTURE