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