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AP Biology, Chapter 27
Prokaryotes and the Origins of Metabolic Diversity
Summary
Introduction
THE WORLD OF PROKARYOTES
They're (almost) everywhere an overview of prokaryotic life
1. Describe the many unique characteristics of prokaryotes. Explain why it might be said
that prokaryotes are the most successful organisms ever to live.
a. Most ancient, small, anucleate
b. Only major taxon found everywhere, in all environments
c. Most numerous
2. Describe the impact of prokaryotes on humans and biological ecosystems.
a. A minority cause disease
b. Most are decomposers, some recycle nutrients in biogeochemical cycles
c. Many form beneficial symbiotic relationships
d. Origin of mitochondria and chloroplasts
Bacteria and archaea are the two main branches of prokaryote evolution
3. Describe the classification of the archaea and the bacteria in the three-domain system.
a. Archaea separated by rRNA sequence and genome structure
b. Archaea inhabit extreme enevironments: acid, salt, hot
c. Molecular studies suggest Archaea and Eukarya share a more recent common
ancestor
d. Prokaryote is a paraphyletic construction
STRUCTURE, FUNCTION, AND REPRODUCTION OF PROKARYOTES
Introduction
4. Describe the general size, organization, and specialization of prokaryotic organisms.
a. Size 1-5 micrometers
b. Unicellular with a few colonial types
c. Rod-shaped bacilli; spherical cocci; spiral spirilli and spirochetes
Nearly all prokaryotes have cell walls external to their plasma membranes
5. Describe the structure, composition, and functions of prokaryotic cell walls.
a. Nearly all have a cell wall with peptidoglycan
b. Functions include shaping, osmotic protection, physical protection
c. Major differences: Gram + and gram 6. Distinguish between the structure and staining properties of gram-positive and gramnegative bacteria. Explain why disease-causing gram-negative bacterial species are
generally more pathogenic than disease-causing gram-positive bacteria.
a. Gram i. Light pink in gram stain
ii. Thin peptidoglycan with second membrane and lipopolysaccharide
(LPS)
iii. Generally more pathogenic
iv. Incl. Salmonella and E. coli
b. Gram +
i. Deep violet in gram stain
ii. Thick peptidoglycan with no second membrane or LPS
iii. More susceptible to lysozyme and penicillin; both act on peptidoglycan
iv. Incl. Bacillus sp.
Many prokaryotes are motile
7. Describe three mechanisms that motile bacteria use to move. Explain how prokaryotic
flagella work and why they are not considered to be homologous to eukaryotic flagella.
a. Three mechanisms
i. Stiff protruding flagella that twirl
ii. Flagella around which the cell is coiled; corkscrews through liquid
iii. Gliding on secreted material
b. Protruding flagella
i. Not homologous: no membrane, no force generated within flagella
ii. Stiff flagella are twirled my a motor embedded in the membrane/wall;
energy from proton gradient
c. Allows movement (taxis) in response to various stimuli
The cellular and genomic organization of prokaryotes is fundamentally different from
that of eukaryotes
8. Explain how the organization of the prokaryotic genome differs from that in eukaryotic
cells.
a. No nuclei; circular chromosome wound into a wad
b. 1/1000 the size of a eukaryotic chromosome; mostly coding
c. Small accessory plasmids may be present
Populations of prokaryotes grow and adapt rapidly
9. List the mechanisms that are sources of genetic variation in prokaryotes and indicate
which one is the major source.
a. Mechanisms of exchange: transformation, transduction, conjugation
b. Major source: new mutation
10. Describe growth as it applies to prokaryotes. Explain what is meant by geometric
growth.
a. Growth is mainly in numbers, not size
b. Geometric = exponential = 124816, etc.
11. Describe the functions of endospores.
a. Endospores are dormant, thick-walled cells
b. Resistant to heat, drying, digestion, poisoning
12. Describe the natural adaptive advantage of antibiotics.
a. Microorganisms produce antibiotics to kill competing cells
b. Antibiotic-producers have some mechanism of resistance
NUTRITIONAL AND METABOLIC DIVERSITY
Introduction
Prokaryotes can be grouped into four categories according to how they obtain energy
and carbon
13. Distinguish between photoautotrophs, chemoautotrophs, photoheterotrophs,
chemoheterotrophs, saprobes, and parasites. Give examples of each.
a. Photoautotrophs
i. Light energy; CO2 for carbon
ii. Cyanobacteria with chlorophyll a, plants, algae, and photosynthetic
bacteria
b. Chemoautotrophs
i. Inorganic compounds for energy; CO2 for carbon
ii. Purple sulfur bacteria
c. Photoheterotrophs
i. Light energy; organic compounds for carbon
ii. Purple non-sulfur bacteria
d. Chemoheterotrophs
i. Organic compounds for energy and carbon
ii. Animals, fungi, a few plants, many bacteria
e. Saprobes
i. Chemoheterotrophs feeding on dead organisms
ii. Include most fungi and bacteria
f. Parasites
i. Chemoheterotrophs feeding on live organisms
ii. Infectious diseases
14. Describe the process and explain the significance of nitrogen fixation.
a. N-fixation = conversion of N2 gas into NH3 by chemoautotrophic bacteria and
photoautotrophic cyanobacteria
b. Other bacteria covert ammonia to nitrites (NO2-) and nitrates (NO3-)
c. Nitrites and nitrates are usable by plants
d. Denitrifying bacteria convert NO2- and NO3- back to N2
15. Distinguish among obligate aerobes, facultative anaerobes, and obligate anaerobes.
a. Obligate aerobes require oxygen for growth
b. Facultative anaerobes can use oxygen but don't need it
c. Obligate anaerobes are killed by oxygen
The evolution of prokaryotic metabolism was both cause and effect of changing
environments on Earth
16. Describe, with supporting evidence, plausible scenarios for the evolution of metabolic
diversity, including the: a) nutrition of early prokaryotes, b) origin of electron transport
chains, c) origin of photosynthesis, d) origin of aerobic respiration.
a. Early prokaryotes
i. ATP and glycolysis appeared early since they are universal
ii. No oxygen; therefore, anaerobes
iii. 5th edition: little organic material; therefore, first came
chemoautotrophs
iv. 6th edition: enough organic material; therefore, first came
chemoheterotrophs
b. Electron transport
i. Chemoautotrophy may have yielded H 2 + energy
ii. Energy may have split H2 giving a proton gradient + free electrons
iii. Membranes capable of manipulating H/electrons would have been
favored
c. Photosynthesis
i. Pigments may have protected from UV
ii. Energized pigments on membranes may have linked with electron
transport/ATP generation
iii. Archaea use bacteriorhodopsin to generate ATP
iv. Cyanobacteria have both photosystems and generate O2
d. Aerobic respiration/oxidative phosphorylation/Krebs cycle
i. Abundant H2O is an advantageous electron donor for photosynthesis
ii. O2 released killed many, some acquired oxygen toleration mechanisms
iii. O2 would have been useful as an electron acceptor
iv. Purple nonsulfur bacteria use a part photosynthesis electron transport
chain for aerobic respiration
PHYLOGENY OF PROKARYOTES
Introduction
Molecular systematics is leading to a phylogenetic classification of prokaryotes
17. Explain how molecular systematics has been used in developing a moneran
classification. Explain why clinical phenotypes are a poor guide to phylogeny.
a. Little fossil evidence and very simple morphologies; rRNA is more useful
b. Clinical phenotypes
i. Shape, gram stain, motility, nutrition
ii. Good for practical ID of common pathogens
iii. Most are polyphyletic
18. Describe the distinguishing features and give examples of the methanogens, extreme
halophiles, and extreme thermophiles. Explain why these groups are collectively known
as extremeophiles.
a. Archaean clades are based solely on comparison of rRNA sequences
b. Major non-clade types
i. Methanogens oxidize H2 using CO2 to produce CH4 in intestines and
rotting material
ii. Halophiles thrive in unusually salty environments; some contain
bacteriorhodopsin
iii. Thermophiles withstand high temperatures
c. Archaeans are much more pervasive than the label "extremeophile" implies
ECOLOGICAL IMPACT OF PROKARYOTES
Introduction
Prokaryotes are indispensable links in the recycling of chemical elements in
ecosystems
19. Describe the role of prokaryotes in recycling within ecosystems.
a. Prokaryotic decomposers release essential nutrients from dead organisms
b. Others convert essential nutrients into usable forms
c. Others replenish the "starting" forms
Many prokaryotes are symbiotic
20. Distinguish among mutualism, commensalism, and parasitism. Describe examples of
prokaryotes in each of these relationships.
a. Mutualism
i. Close association in which both benefit
ii. Intestinal flora completes digestion, makes vitamins
iii. Nitrogen fixing bacteria live in legume root nodules
b. Commensalism
i. One benefits, the other is neutral
ii. Most bacteria on and in humans are commensals
c. Parasitism
i. One benefits, one is harmed
ii. Bacterial diseases like tuberculosis, leprosy, and anthrax
21. List Koch's postulates, which are used to substantiate a specific pathogen as the
cause of a disease.
a. Find the suspected pathogen in each individual with the disease
b. Isolate it from a diseased individual and grow it in the laboratory
c. Cause the disease by infecting from the culture
d. Re-isolate the pathogen from the experimental infection
Humans use prokaryotes in research and technology
22. Distinguish between exotoxins and endotoxins and describe examples of each.
a. Exotoxin
i. Toxic substances secreted by pathogens
ii. Ex.: Clostridium botulinum makes botulinum toxin
iii. Ex.: Vibrio cholerae makes cholera toxin
b. Endotoxin
i. Toxic substances that are part of the cell wall/membrane
ii. Ex.: lipopolysaccharide in Salmonella
23. Describe how Streptomyces can be used commercially.
a. Production of many useful antibiotics
24. Describe the limitations of antibiotics in combating bacterial diseases.
a. Bacteria microevolve resistance
b. We're running out of easily assessed microbiodiversity
25. Describe how humans exploit the metabolic diversity of prokaryotes for scientific and
commercial purposes.
a. "Simple" microbes like E. coli are exhaustively studied
b. Fermentation makes food and medicines
c. Bacteria may help break down pollutants