Ch. 27 Bacteria
and Archaea
Objective:
Understand the general structure and motility of
bacteria and how genetic recombination
increases diversity.
27.1 Structural and Functional Adaptations
Contribute to Prokaryotic Success
1 m
1 m
3 m
• Very adaptable (extreme salt, pH, and temp).
• Most are unicellular (0.5-5 um) but still perform all of
life’s functions.
(a) Spherical
(b) Rod-shaped
(c) Spiral
Cell Surface Structures
• All bacteria have a cell wall.
• Archaeal bacteria do NOT have a layer of
peptidoglycan in their cell walls.
• Eubacteria have differing amount of peptidoglycan
o Gram positive: stains violet due to thick layer peptidoglycan.
o Gram negative: stains red due to extra membrane past
peptidoglycan.
(a) Gram-positive bacteria: peptidoglycan traps crystal violet.
Gram-positive
bacteria
(b) Gram-negative bacteria: crystal violet is easily rinsed
away, revealing red dye.
Gram-negative
bacteria
Carbohydrate portion
of lipopolysaccharide
Cell
wall
Peptidoglycan
layer
Outer
membrane
Cell
wall
Plasma
membrane
10 m
Peptidoglycan
layer
Plasma membrane
Motility
• About half of known bacteria can move (taxis)
toward/away from a stimulus
o Most commonly via flagella either surrounding the body or found at 1
end. Works like a helicopter with a motor, hook, and filament.
Flagellum
Filament
Hook
Motor
Cell wall
Plasma
membrane
Rod
Peptidoglycan
layer
20 nm
Internal Organization and
DNA
• No membrane bound organelles but plasma
membrane folds on itself to make metabolic
membranes.
1 m
0.2 m
Respiratory
membrane
Thylakoid
membranes
(a) Aerobic prokaryote
(b) Photosynthetic prokaryote
Internal Organization and
DNA
• Smaller, circular DNA found in nucleoid (not
nucleus) with very small plasmids (self replicating
DNA)
Chromosome
Plasmids
1 m
Reproduction and Adaptation
• Reproduce every couple of hours (under optimal
conditions) by binary fission.
o Division stops due to space limits, metabolic toxins, eaten, etc.
o Short generation time leads to quick evolution.
Reproduction and Adaptation
• Endospores develop in harsh conditions.
o Duplicated DNA in a tough, multilayered structure.
o Water is removed and metabolism stops.
Endospore
Coat
0.3 m
27.2 Rapid Reproduction, Mutation, and Genetic
Recombination Promote Genetic Diversity in
Prokaryotes
• 3 mechanisms for prokaryotic genome
combinations
o Transformation
o Transduction
o Conjugation
Transformation
• Changes genotype
and phenotype by
uptake of foreign DNA
o Ex: harmless strains of the
bacteria that can cause
pneumonia become
pathogenic if they come in
contact with a pathogenic
cell.
Transduction
Phage
• A “mutant” phage
with bacterial DNA
infects a bacteria
cell.
A B
Donor cell
A B
A
Recombination
A
A B
Recipient
cell
A B
Recombinant cell
1 m
Sex pilus
Conjugation
• A donor bacteria makes a copy of its DNA,
attaches to another bacteria via a (sex) pilus, the
DNA travels to recipient forming a recombined cell.
Bacterial chromosome
F plasmid
F cell
(donor)
F cell
Mating
bridge
F cell
(recipient)
F cell
Bacterial
chromosome
(a) Conjugation and transfer of an F plasmid
Hfr cell
(donor)
A
A
A
F factor
F cell
(recipient)
A
A
A
A
(b) Conjugation and transfer of part of an Hfr bacterial chromosome
A
A
A
Recombinant
F bacterium