Aim: What is the heterotroph hypothesis?

1. Aim: What is the heterotroph hypothesis?

2. Early history of life • Solar system~ 12 billion years ago (bya) • Earth~ 4.5 bya • Life~ 3.5 to 4.0 bya • Prokaryotes~ 3.5 to 2.0 bya stromatolites • Oxygen accumulation~ 2.7 bya photosynthetic cyanobacteria • Eukaryotic life~ 2.1 bya • Muticelluar eukaryotes~ 1.2 bya • Animal diversity~ 543 mya • Land colonization~ 500 mya

4. Earth formed 4.6 billion years ago The oldest fossil organisms are prokaryotes dating back to 3.5 billion years ago Prokaryotes are single-celled organisms in the domains Bacteria and Archaea Some of the earliest prokaryotic cells lived in dense mats that resembled stepping stones Overview: The First Cells

5. Prokaryotes are the most abundant organisms on Earth There are more in a handful of fertile soil than the number of people who have ever lived Prokaryotes thrive almost everywhere, including places too acidic, salty, cold, or hot for most other organisms Some prokaryotes colonize the bodies of other organisms

6. The Origin of Life • Spontaneous generation vs. biogenesis (Pasteur) • The 4-stage Origin of life Hypothesis: • 1- Abiotic synthesis of organic monomers • 2- Polymer formation • 3- Origin of Self-replicating molecules • 4- Molecule packaging (“protobionts”)

7. Organic monomers/polymer synthesis • Oparin (Rus.)/Haldane (G.B.) hypothesis (primitive earth): volcanic vapors (reducing atmosphere) with lightning & UV radiation enhances complex molecule formation (no O2) • Miller/Urey experiment: • water, hydrogen, methane, ammonia • all 20 amino acids, nitrogen bases, & ATP formed • Fox proteinoid formation (abiotic polypeptides) from organic monomers dripped on hot sand, clay or rock • Oparin (coacervates) protobionts (aggregate macromolecules; abiotic) surrounded by a shell of H2O molecules coated by a protein membrane

8. Protocells Replication and metabolism are key properties of life and may have appeared together Protocells may have been fluid-filled vesicles with a membrane-like structure In water, lipids and other organic molecules can spontaneously form vesicles with a lipid bilayer

10. Abiotic genetic replication • First genetic material • Abiotic production of ribonucleotides • Ribozymes (RNA catalysts) • RNA “cooperation” • Formation of short polypeptides (replication enzyme?) • RNA~ DNA template?

11. Self-Replicating RNA The first genetic material was probably RNA, not DNA RNA molecules called ribozymes have been found to catalyze many different reactions For example, ribozymes can make complementary copies of short stretches of RNA

12. Natural selection has produced self-replicating RNA molecules RNA molecules that were more stable or replicated more quickly would have left the most descendant RNA molecules The early genetic material might have formed an “RNA world” Vesicles with RNA capable of replication would have been protocells RNA could have provided the template for DNA, a more stable genetic material

13. The Major Lineages of Life