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Chapter 27) Prokaryotes and the Origins of Metabolic Diversity p. 526-535
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The World of Prokaryotes
o They’re (almost) everywhere! An overview of prokaryotic life
 prokaryotes have the biggest biological mass; found wherever life is + cold, hot, salty, acidic, and
alkaline environments
 prokaryotes can cause disease, provide vitamins, prevent harmful bacteria growth, carbon cycle, etc.
o Bacteria and archaea are the two main branches of prokaryote evolution
 domain: taxonomic level above kingdom – Domain Bacteria, Archaea, and Eukarya
The Structure, Function, and Reproduction of Prokaryotes
o most prokaryotes are unicellular, but some stay together in groups/colonies
o 3 most common prokaryote shapes: cocci (spheres), bacilli (rods), and spirilla/spirochetes (helices)
o Nearly all prokaryotes have a cell wall external to the plasma membrane
 cell wall function – maintain shape, protection, prevents bursting in hypotonic environment
 unlike plant cell walls, bacteria walls contain peptidogylcan: made of sugar polymers cross-linked by
various short polypeptides
 gram stain: used to separate species into two groups of different cell walls – gram-positive: have
simpler cell walls with a lot of peptidogylcan; gram-negative: less peptidogylcan and more complex
cell wall structures (has an outer membrane with lipopolysaccharides)
 gram-negative pathogenic bacteria is usually more dangerous than gram-positive pathogenic
bacteria because the lipopolysaccharides are toxic & are more resistant to antibiotics
 antibiotics: inhibit synthesis of cross links in peptidogylcan/prevent formation of cell wall
 capsule: sticky protective layer outside the cell wall secreted by some prokaryotes
 pili: appendages of some prokaryotes that allow them to attach to other prokaryotes
o Many prokaryotes are motile
 flagellar action: most common kind of prokaryotes’ movement; flagella are smaller than and not
covered by plasma membrane like in eukaryotes
 spirochetes have helical filaments that have a basal motor – when the filaments rotate, the cell
moves like a corkscrew
 some prokaryotes secrete slimy threads that anchor to the substratum – prokaryote glides along the
growing ends of threads
 taxis: movement toward or away from a stimulus
o The cellular and genomic organization of prokaryotes is fundamentally different from that of eukaryotes
 prokaryotes metabolic functions are done by specialized membranes in the plasma membrane
 prokaryotes have less DNA than eukaryotes, and it is in a fiber in a nucleoid region
 genophore: bacterial chromosome (which is very different than eukaryotic chromosomes)
 plasmids: small rings of only few genes; not essential; replicate independently of main
chromosome; can be transferred between prokaryotes
 prokaryotic ribosome is smaller and has different protein and RNA content than eukaryotic – allows
certain antibiotics to bind to prokaryotic ribosomes and not eukaryotic
o Populations of prokaryotes grow and adapt rapidly
 binary fission: prokaryotes’ mode of cell division
 transformation: prokaryotic cell takes genes from surrounding environment
 conjugation: direct transfer of genes between prokaryotes
 transduction: viruses transfer genes between prokaryotes
 endospores: resistant cells that allow prokaryotes to stand harsh conditions; can “turn off and on”
depending on conditions (harsh vs. not harsh)
 antibiotics: chemicals that inhibit the growth of other microorganisms; part of competition for
resources; used by humans to fight pathogenic bacteria
Nutritional and Metabolic Diversity
o Prokaryotes can be grouped into four categories according to how they obtain energy and carbon
 organisms organized into 4 groups based on nutrition: how organism gets energy and carbon (for
building organic molecules of cells)
Daniel Oh 2014
Monday, December 17, 2012 4:21:04 PM Central Standard Time
Nutritional Diversity Among Chemoheterotrophs
o saprobes: decomposers that absorb nutrients from dead organic matter
o parasites: absorb nutrients from body fluid of living host
o Lactobacilli have specific nutritional needs, E. coli are less particular
o nonbiodegradable: classes of synthetic organic compounds that cannot be broken down by
chemoheterotrophs
• Nitrogen Metabolism
o Nitrosomonas convert ammonium to nitrite, Pseudomonas “denitrify” soil nitrite/nitrate,
and some cyanobacteria use atmospheric nitrogen as nitrogen source (nitrogen fixation:
converting atmospheric nitrogen to ammonium)
• Metabolic Relationships to Oxygen
o obligate aerobes: use O2 for cellular respiration and cannot grow without it
o facultative aerobes: use O2 if available, but can grow by fermentation
o obligate anaerobes: poisoned by O2; some live just by fermentation, others by anaerobic
respiration (inorganic molecules other than O2 accept electrons at the end of the chains)
Photosynthesis evolved early in prokaryotic life
 very first prokaryotes were probably heterotrophs that got energy and carbon skeletons from
organic molecule pool on Earth – glycolysis was probably one of the first metabolic pathways
 hypothesis(a): photosynthesis evolved many times – photosynthesis evolved independently many
times in different prokaryotic lineages (less likely since photosynthesis is complex)
 hypothesis(b): photosynthesis evolved once – photosynthesis evolved in very early prokaryotic life
and some lineages lost photosynthesis
 evolution of cyanobacteria: evolved from ancestors with nonoxygenic photosynthesis; evolution
transformed atmosphere from reducing to oxidizing
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Daniel Oh 2014
Monday, December 17, 2012 4:21:04 PM Central Standard Time