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Ch. 27 Bacteria and
ArchaeaObjective:
Understand the general structure and motility of bacteria and how genetic recombination increases
diversity.
27.1 Structural and Functional Adaptations Contribute to Prokaryotic
Success• 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
1
m
1
m
3
m
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-positivebacteria
Peptido-glycanlayer
Cellwall
Plasmamembrane
10 m
Gram-negativebacteria
Outermembrane
Peptido-glycanlayer
Plasma membrane
Cellwall
Carbohydrate portionof lipopolysaccharide
(b) Gram-negative bacteria: crystal violet is easily rinsed away, revealing red dye.
Motility• About half of known bacteria can move (taxis)
toward/away from a stimuluso Most commonly via flagella either surrounding the body or found at 1
end. Works like a helicopter with a motor, hook, and filament.
Flagellum
HookMotor
Filament
RodPeptidoglycanlayer
Plasmamembrane
Cell wall
20 nm
Internal Organization and DNA
• No membrane bound organelles but plasma membrane folds on itself to make metabolic membranes.
(a) Aerobic prokaryote (b) Photosynthetic prokaryote
Respiratorymembrane
Thylakoidmembranes
0.2 m 1 m
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.
Coat
Endospore
0.3 m
27.2 Rapid Reproduction, Mutation, and Genetic Recombination Promote Genetic Diversity in
Prokaryotes
• 3 mechanisms for prokaryotic genome combinationso Transformationo Transductiono Conjugation
Transformation• Changes genotype
and phenotype by uptake of foreign DNAo Ex: harmless strains of the
bacteria that can cause pneumonia become pathogenic if they come in contact with a pathogenic cell.
Transduction• A “mutant” phage
with bacterial DNA infects a bacteria cell.
Recombinant cell
Recipientcell
Recombination
A
A
A B
BA
Donor cell
A B
BA
Phage
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.
Sex pilus
1 m
F plasmid Bacterial chromosome
F cell(donor)
F cell(recipient)
Matingbridge
Bacterialchromosome
(a) Conjugation and transfer of an F plasmid
Hfr cell(donor)
F cell(recipient)
(b) Conjugation and transfer of part of an Hfr bacterial chromosome
F factor
A
A
A
A
A
A A
F cell
F cell
AA
RecombinantF bacterium
A
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