Origins and Evolution of Microbial Life on Earth

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

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

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.

Stages of Early Life Formation • 1) Inorganic materials allowed 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.

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.

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.

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”

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.

Archaea & Bacteria (Table p. 325) • Prokaryotes found on Earth from 3. 5 bya to 1. 5 bya. • Differences between Archaea and Bacteria: – Short r. RNA sequences – RNA polymerases – Introns – Antibiotic sensitivity – Cell walls / membranes (peptidoglycan & lipids)

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

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

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Prokaryotes & Nutrition • Autotrophs: Make own organic compounds. Obtaining energy from sunlight or inorganic compounds. –Photoautotrophs (E = sunlight & C = CO 2) –Chemoautotrophs* (E = inorganic chem. ) [*Earilest life-form]

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

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.

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

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.

Origins of Eukaryotic Cell • Mitochondria thought to have evolved 1 st 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.

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.

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

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

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.

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)

Multicellular Algae • Alteration of Generations: multicellular diploid (2 n)[sporophyte] alternates with a multicellular haploid (n) [gametophytes] • Developed via colonies of unicellular protists. • Figure 16. 25