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Bacteria and Archaea
CHAPTER 27
YOU MUST KNOW
 The key ways in which prokaryotes differ from
eukaryotes with respect to:
Genome;
 Membrane bound organelles;
 Size;
 Reproduction
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 Mechanisms that contribute to genetic diversity in
prokaryotes, including:
Transformation;
 Conjugation;
 Transduction;
 Mutation

Structural & Functional Adaptations
 Structural and functional adaptations contribute to
prokaryotic success:
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Both the domain Bacteria and the domain Archaea are made
up of prokaryotes.
Prokaryotes have NO TRUE NUCLEI or internal
compartmentalization.
The DNA of prokaryotes is concentrated in the nucleoid region
and has little associated protein.
Relative to eukaryotes, prokaryotes have simple, small
genomes.
In addition to their one major chromosome, prokaryotic cells
may also possess smaller, circular, independent pieces of DNA
called plasmids.
Prokaryotic Shapes
 In general, prokaryotes exist in three common
shapes:
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Cocci (round)
Bacillus (rod-shaped)
Spirilla (spiral)
Prokaryotic Reproduction
 Prokaryotes reproduce through an asexual process
called binary fission, and they continually synthesize
DNA.
Prokaryotic Structure
 Outside their cell membranes, most prokaryotes
possess a cell wall that contains peptidoglycan.
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Gram-positive bacteria have simpler cell walls with more
peptidoglycan.
Gram-negative bacteria have cell walls that are structurally
more complex.
Prokaryotic Structure
 The cell wall of many prokaryotes is covered by a
capsule, a sticky layer of polysaccharide or protein.
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The capsule enables prokaryotes to adhere to other substrate
or to other individuals in a colony. Some capsules protect
against dehydration.
 Some prokaryotes stick to their substrate or to one
another by means of hair-like appendages called
fimbriae.
 The ability of some prokaryotes to withstand harsh
conditions is attributed to endospores, a tough wall
that forms outside the cell wall.
Prokaryotic Motility
 Prokaryotes use appendages called pili that adhere to each other or to
surrounding surfaces.
 About half of the prokaryotes are motile, because they possess whiplike
flagella.
Genetic Diversity in Prokaryotes
 Rapid reproduction, mutation, and genetic
recombination promote genetic diversity in
prokaryotes:
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While mutation is the major source of genetic variation in
prokaryotes, there are three mechanisms by which bacteria can
transfer genetic material between each other:
1.
2.
3.
Transformation (the uptake of foreign DNA from the
surrounding environment).
Conjugation (the direct transfer of genes from one prokaryote to
another).
Transduction (the transfer of genes from one prokaryote to
another via a viral vector).
Lateral Gene Transfer in Prokaryotes
Major Nutritional Modes in Prokaryotes
Oxygen Needs in Prokaryotes
 Obligate aerobes cannot growth without oxygen
because they need oxygen for cellular respiration.
 Obligate anaerobes are poisoned by oxygen. Some
use fermentation, whereas others extract chemical
energy by another form of anaerobic respiration.
 Facultative anaerobes use oxygen if it is available,
when oxygen is not available, they undergo
fermentation.
 Some prokaryotes can use atmospheric nitrogen as a
direct source of nitrogen in a process called nitrogen
fixation. They convert N2 to NH4+.
Molecular Systematics & Prokaryotic Phylogeny
 Molecular systematics is illuminating prokaryotic
phylogeny.
 The first prokaryotes that were classified in the
domain Archaea are known as extremophiles and
live in extreme environments:
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Extreme Halophiles: live in saline environments.
Extreme Thermophiles: live in very hot environments.
 Other Archaea do not live in extreme environments.
 Methanogens use carbon dioxide to oxidize H2 and produce
methane as a waste product.
Ecological Importance of Prokaryotes
 Prokaryotes play crucial roles in the biosphere:
 Many prokaryotes are decomposers, breaking down dead
organic matter.
 Many prokaryotes are symbiotic, forming crucial relationships
with other species.
 Some prokaryotes are pathogenic and cause illness by
producing poisons. Antibiotics are chemicals that can kill
prokaryotes. They are NOT effective against viruses.

Many bacterial plasmids contain resistance genes to different
antibiotics.
Human Uses of Prokaryotes
 Prokaryotes are used by humans in many ways:
 Prokaryotes are used in bioremediation, removing pollutants
from soil, air, or water.
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Includes sewage treatment, oil spill clean up, and radioactive
material precipitation.
Prokaryotes are symbionts in the gut, and can be used to make
vitamins, and assist in digesting food.
Prokaryotes are used in gene cloning and producing transgenic
organisms.
Prokaryotes are used in a wide variety of food productions:
cheese, yogurt, and other products.