The History of Life

1. The History of Life Chapter 14: First Cells and Endosymbiosis

2. Progression of Life • 4.5 – 4.0 billion years ago – formation of the earth. • Between 4.0 – 3.5 bya – Formation of Organic compounds • 3.8 – 3.5 bya – FIRST cells appeared. First cells are believed to have been anaerobic, prokaryotic and heterotrophic.

3. Where did Organic Compounds Come From? • In 1953 Stanley Miller and Harold Urey performed an experiment which proved that organic compounds (carbohydrates, lipids, proteins, and nucleic acids) could be synthesized on early Earth using the harsh conditions and atmospheric gases. • Organic compounds could have been carried to Earth from space. In 1970 organic compounds found in meteorites.

4. Organic Compounds to Cell-like Structures (precursors of life) • Scientists have not been able to successfully construct a living cell from organic molecules in the laboratory. • In their search for the link between organic molecules and cells, scientists constructed the following: • Microspheres • Coacervates

5. Precursors of Life • MICROSPHERES spherical in shape and are composed of many protein molecules ahta are organized as a membrane • COACERVATES: collections of droplets that are composed of molecules of different types, including lipids, amino acids and sugars.

6. What characteristics did precursors share with CELLS? • Organized • Ability to take up certain substances from their surroundings. • Coacervates can grow • Microspheres can bud to form smaller microspheres BUT: Microspheres and Coacervates did not have hereditary characteristics.

7. First Life Forms and Heredity • Scientists continue to investigate to explain how molecules could be organized into self-replicating systems. • Scientists need to explain the origin of heredity. • Early 1980’s Thomas Cech discovered RNA that can act as a catalyst. Ribozyme – an RNA molecule that can act as a catalyst to promote a specific chemical reaction.

8. RNA and Self-Replicating System • Scientists believe that RNA may have been the first molecule of heredity for the cell-like structures.

9. The First Cells • Fossil evidence supports that the first cells appeared on earth about 3.5 billion years ago. • The first cells were heterotrophic and fed upon the organic molecules in the oceans. • The first cells were prokaryotic. • The atmosphere of early earth did not contain oxygen so the first cells were anaerobic.

10. Chemosynthesis • Archea bacteria survive in harsh conditions. • Conditions on early earth were harsh. • Scientists believed that early autotrophic prokaryotes were similar to the Archea bacteria alive today. • Some Archea bacteria are obligate anaerobes and are able to undergo cheomosynthesis.

11. Photosynthesis • Some forms of life became photosynthetic by 3 billion years. • Fossils similar to modern cyanobacteria (blue-green algae) were found in layered structures called stromatolites. • Photosynthesis led to the build up of oxygen in the atmosphere. • The build up of oxygen led to the formation of the ozone layer. • The build up of oxygen also led to aerobic cellular respiration.

12. Prokaryotes to Eukaryotes! • Evidence suggests that eukaryotes appeared on Earth between 2.0 billion and 1.5 billion years ago. • Scientists suggest that eukaryotes were formed by a process known as endosymbiosis. • Evidence which supports the endosymbiosis theory is seen in mitochondria and in chloroplasts.

13. Endosymbiosis • Endosymbiosis Theory suggests that the mitochondria and chloroplasts were once free-living prokaryotes that got surrounded and engulfed by other larger prokaryotes. • Evidence that supports this theory include: • Both the mitochondria and chloroplast have their own DNA. • Both the mitochondria and chloroplast have their own membrane and are about the size of a prokaryote.

14. Endosymbiosis

15. Good luck on the TEST! • Reminder that the TEST on Chapter 14: The History of Life and related concepts is scheduled for Thursday, May 6, 2010. • Remember to check the answers to the 14-1 and 14-2 Section Review Worksheets. • Answers are available online at the Monkemeier Teacher Web page after 6 p.m. on Monday, May 3, 2010