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