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 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.

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 rRNA sequences RNA polymerases Introns Antibiotic sensitivity Cell walls / membranes (peptidoglycan & lipids)

Archaea Abundant in many environments Extreme 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 = CO2) 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 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.

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 (2n)[sporophyte] alternates with a multicellular haploid (n) [gametophytes] Developed via colonies of unicellular protists. Figure 16.25