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Prokaryotes. The Origins of Metabolic Diversity. Lightning Strike. The World of Prokaryotes. Prokaryotes were the earliest organisms They are not only the most numerous organisms, but also the most pervasive Prokaryotes are microscopic and perform vital functions

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The Origins of Metabolic Diversity

Lightning Strike

The world of prokaryotes
The World of Prokaryotes

  • Prokaryotes were the earliest organisms

  • They are not only the most numerous organisms, but also the most pervasive

  • Prokaryotes are microscopic and perform vital functions

  • Prokaryotes often live in symbiotic relationships – endosymbiosis

p. 502 - 503

Tornado on the road

p. 503

Point of reference

An explosion of diversity
An Explosion of Diversity

  • Modern prokaryotes are diverse in structure and physiology

  • About 5000 species are known

  • Estimated range: 400,000 – 4 million

  • “A true sense of biodiversity requires a “downward adjustment of scale”

p. 503

Hydrogen Explosion

Bacteria and archaea
Bacteria and Archaea

  • The two main branches of prokaryotic evolution

  • Archaeabacteria are much closer to eukaryotes than they are to eubacteria

  • Archaea inhabit extreme environments (hot springs, salt ponds, thermal vents)

A thermal vent 

p. 503

Cool Harvard Cell Video

Prokaryotic structure
Prokaryotic Structure

  • Most prokaryotes are unicellular

  • Some species tend to form aggregates

  • Others form true colonies while few exhibit multicellular characteristics

  • Nearly all prokaryotes have cell walls external to their plasma membranes

  • Bacterial walls consist of peptidoglycan (polymer of modified sugars cross-linked with short polypeptides); archaea lack peptidoglycan

p. 504

Cool Harvard Cell Video

Average prokaryote diameter:

1 – 5 μm

Average eukaryotic diameter:

10 – 100 μm

The largest prokaryote:

Bacilli measuring ½ mm

p. 504

Among pathogens, gram-negative are more threatening because they are more resistant to antibiotics (i.e. penicillin) that degrade peptidoglycan

Capsule: sticky protective secretion on prokaryotes that provides protection

Gram stains:

Gram-positive: simpler walls and abundant peptidoglycan

Gram-negative: complex with low peptidoglycan; outer membrane contains lipopolysaccharides (carbohydrate bonded to lipid)


  • About half of prokaryotes are motile

  • Many move through solutions of water, ions, and other solutes

  • Many motile prokaryotes can move about 50 μm/sec

  • Flagellar movement

  • Spirochete movement

  • Most are capable of taxis (movement toward/away from a stimulus

  • Magnetic particles establish up and down

  • Photosynthetic bacteria show positive phototaxis


p. 506


Cellular and genomic organization
Cellular and Genomic Organization

  • Prokaryotes lack the extensive eukaryotic compartmentalization

  • Bacteria have smaller, simpler genomes

  • Genophore – prokaryotic chromosome

  • DNA is concentrated in a snarl of fibers in a nucleoid region

  • Plasmids may also be present

  • The prokaryotic ribosome is smaller

p. 506

Black Hole in Space

Reproduction and variation
Reproduction and Variation

  • Binary fission – continuous DNA synthesis and indefinite asexual multiplication

  • Three methods of genetic recombination:

    • Transformation – genetic material taken from the environment

    • Conjugation – genes transferred directly between prokaryotes via sex pilius

    • Transduction – genes transferred between prokaryotes and viruses

  • Mutation remains the largest source of variation

  • Populations of prokaryotes grow and adapt rapidly

  • Growth in prokaryotes refers to population size more than individual cell enlargement

  • Some bacteria form resilient cells called endospores around their DNA, encasing it against most degrading elements

Variations in endospore morphology

(1, 4) – Central endospore (2, 3, 5) – Terminal endospore (6) – Lateral endospore

p. 507

Binary Fission

Nutritional and metabolic diversity
Nutritional and Metabolic Diversity

  • Photoautotroph – Organisms that harness light energy to drive photosynthesis with CO2 (cyanobacteria)

  • Chemoautotroph – Organisms that need only CO2 to oxidize inorganic substances with chemical energy from hydrogen sulfide (H2S), ammonia (NH3), and ferrous ions (Fe2+) or other molecules

  • Photoheterotroph – Organisms that use light to generate ATP, but obtain carbon in organic form

  • Chemoheterotroph – Organisms that consume organic molecules for both energy and carbon

p. 508

The Toba Eruption

Nutritional diversity among chemoheterotrophs
Nutritional Diversity Among Chemoheterotrophs

  • Saprobes: Decomposers that absorb their nutrients from dead organic matter

  • Parasites: Organisms that absorb their nutrients from body fluids of living hosts

  • Nitrogen Metabolism

    • Nitrogen fixation p. 1141

p. 508 – 509

Supernova Explosion

Metabolic relationships to oxygen
Metabolic Relationships to Oxygen

  • Obligate aerobes use O2 for cellular respiration and cannot grow without it

  • Obligate anaerobes are poisoned by O2 which live either exclusively on fermentation or extract chemical energy through anaerobic respiration

  • Facultative anaerobes will use O2 is it is present but can also undergo fermentation

p. 509


The bacteria song

The Bacteria Song!!!

Before we move to some facts…

Fun facts
Fun Facts

  • Prokaryotes have a higher metabolic rate than eukaryotes due to their large surface area to volume ratio

  • Cyanobacteria often live in differentiated colonies, showing small signs of specialization

  • We are made of dead star meterial

  • Black holes are gravity’s revenge on mass

Neptune’s Great Dark Spot