Origins and Evolution of Microbial Life (on Earth)

1. Origins and Evolution of Microbial Life (on Earth) Chapter 16

2. Early Life Topics • Stanley Miller • Early Polymers • RNA = genetic material / enzymes • Membranes • Archaea & Bacteria • Prokaryotes: Structure & Function • Protists (Unicellular Eukaryotes)

3. Early Lifeforms (“Earthlings”) • First living organisms came into being between 3.9 and 3.5 billion years ago!!! (earth is ~4.5 byo) • Aggregates of molecules (inorganics) that performed metabolic reactions and self-replication.

4. Stages of Early Life Formation • 1) Inorganicmaterials allowed for formation of organic materials. • 2) Formation of polymers from organic materials. • 3) Polymer replication (form of heredity) • 4) Polymers chemical composition became distinct form environment.

5. Stanley Miller Experiments • 1953, demonstrated how amino acids and organic molecules could be generated from basic chemicals found on early Earth. • Simple Materials + Energy = Complex Materials • Occurrence around submerged volcanoes / hydrothermal vents.

6. Early Polymers • Early polymerization of macromolecules may not have needed enzymes, but rather used process of Vaporization. • Same function as dehydration synthesis reaction in forming polymers. • Importance of clay: has electric charged areas = catalyzed early dehydration synthesis reactions.

7. RNA = Early Genetic Material & Enzymatic Functioning • Early genes are thought to have been short strands of RNA. • Did not require enzymes (Fig. 16.5) • Clay with metals serve as a catalyst. • Ribozymes - RNA that can catalyze reactions. • “RNA World”

8. Membranes (Molecular “co-ops”) • Spheres of fluid, RNA, polypeptides, lipids, and other organic molecules may have formed in small aquatic environments. • Potential to absorb molecules, divide, swell & shrink (osmosis). • Molecular “co-ops” would be favored by natural selection - function of metabolism & replication.

9. Archaea & Bacteria (Table p. 325) • Prokaryotes found on Earth from 3.5 bya to 1.5 bya. • Differences between Archaea and Bacteria: • Short rRNA sequences • RNA polymerases • Introns • Antibiotic sensitivity • Cell walls / membranes (peptidoglycan & lipids)

10. Archaea • Abundant in many environments • Oceans • Extreme Environments: • Salty places - halophiles • Ex: Dead Sea • Hot places - thermophiles • Ex:Deep-ocean vents • Methane-rich places - methanogens

11. Prokaryotes: Structure and Function • Prokaryotic Cell Shape: • Cocci (spherical): • Ex: staphylococci & streptococci • Bacilli (rod-shaped): • Ex: diplobacilli & streptobacilli • Spirilla (curved, spiral) • Ex: Spirochete

12. http://www.cfsan.fda.gov/~dms/a2z-b3.gif

13. Prokaryotes & Nutrition • Autotrophs: Make own organic compounds. Obtaining energy from sunlight or inorganic compounds. • Photoautotrophs (E = sunlight & C = CO2) • Chemoautotrophs* (E = inorganic chem.) [*Earilest life-form]

14. Prokaryotes & Nutrition • Heterotrophs: Obtain carbon from organic compounds. • Photoheterotrophs (E & C = organics) • Chemoheterotrophs ** (E = any organic) [**Dominant forms today]

15. Prokaryotes: Structure and Function • Flagellum - enable propellar-like motion; naked protein structure. • Pili - allow bacteria to adhere to surface , as well as each other (Sex pili - conjugation) • Endospore - dehydrated inner cell. Used for protection against harsh environmental conditions.

16. Origins of Eukaryotic Cell • Eukaryotes evolved from prokaryotes more than 2 bya. • 2 Processes: • 1) Membrane Infolding = all membrane-enclosed organelles except mitochondria and chloroplasts. • Figure 16.17 A & B

17. Origins of Eukaryotic Cell • 2)Endosymbiosis = chloroplasts and mitochondria evolved form small prokaryotes that established residence within other, larger prokaryotes. • Dependence on host cell for inorganic molecules. • Host cell obtained ATP & organic molecules from chloro/mito.

18. Origins of Eukaryotic Cell • Mitochondria thought to have evolved 1st b/c of their presence in all eukaryotic cells. • Chloroplasts only in some eukaryotic cells. • Both organelles contain small amounts of DNA, RNA, and ribosomes. • Both organelles transcribe/translate own DNA, replicate, reproduce via binary fission.

19. Protists (Unicellular Eukaryotes) • Algae = protists that photosynthesize. • Potozoa = heterotrophic, consume other protists and bacteria. • Found in both Aerobic & Anaerobic aquatic environments. • Structure = membrane-bound nucleus, flagella/cillia with 9+2 pattern of microtubules.

20. 4 major Groupings of Protists • Protozoa • Slime molds • Unicellular algae • Multicellular algae

21. Protozoa • Have heterotrophic mode of nutrition. • Found in all kind of aquatic environments • Categories of Protozoa: • A) flagellates • B) amoebas • C) apicomplexans • D) ciliates

22. Slime Molds • Have unicellular and multicellular life stages. • Obtain food from digesting other organisms. • When food supplies are low, switch to multicellualr reproductive stage of its life cycle. • Useful in studying chemical changes that cause cellular differentiation.

23. Unicellular Algae • Photosynthesis: carbon dioxide and water are primary sources of food. • Have chloroplasts that contain chlorophyll a molecule (same as plants). • Unicellular & colonial Algal groupings: • Dinoflagellates • Diatoms • Green algae (ancestors of first plants)

24. Multicellular Algae • Alteration of Generations: multicellular diploid (2n)[sporophyte] alternates with a multicellular haploid (n) [gametophytes] • Developed via colonies of unicellular protists. • Figure 16.25