Download Bacteria

Staphylococcus bacteria in nose
Bacteria
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Structure
• Unicellular
• Some species form colonies
• 0.5–10 µm, much smaller
than the 10–100 µm of
many eukaryotic cells
• Most common shapes:
• spheres (cocci)
• rods (bacilli)
• and spirals
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Bacterial Cell Wall
• maintains cell shape
• provides physical protection,
sugar
sugar
• prevents the cell from bursting in a hypotonic
environment
polypeptide
• Bacterial cell walls contain peptidoglycan, a
network of sugar polymers cross-linked by
polypeptides (proteins)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Gram Stain Classification
• Using the Gram stain, scientists classify
bacterial into Gram + or Gram - groups based
on cell wall composition
• Gram - bacteria:
• less peptidoglycan
• outer membrane that can be toxic
 more likely to be antibiotic resistant
Gram Gram +
• Many antibiotics target peptidoglycan and
damage bacterial cell walls
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Cell
wall
Peptidoglycan
layer
Plasma membrane
Protein
(a) Gram-positive: peptidoglycan traps
crystal violet.
Carbohydrate portion
of lipopolysaccharide
Outer
membrane
Cell
wall Peptidoglycan
layer
Plasma membrane
Protein
(b) Gram-negative: crystal violet is easily rinsed
away, revealing red dye.
Grampositive
bacteria
Gramnegative
bacteria
20 µm
Structure
• A polysaccharide or protein layer called a
capsule covers many bacteria
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Bacterial Motility
• Most motile bacteria use flagellato propel
themselves
• Many exhibit taxis, the ability to move toward
or away from certain stimuli
Video: Prokaryotic Flagella (Salmonella typhimurium)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Flagellum
Filament
50 nm
Cell wall
Hook
Basal apparatus
Plasma
membrane
Fimbriae
Fimbriae (also called attachment pili)
• allows them to stick to their substrate or other
individuals in a colony
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Internal Organization
• lack complex compartmentalization (ex. no
nucleus, ER, mitochondrion, etc.)
• Often perform metabolic functions using highly
folded extensions of plasma membrane
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
1 µm
0.2 µm
Respiratory
membrane
Thylakoid
membranes
(a) Aerobic prokaryote
(b) Photosynthetic prokaryote
Genome
• Most of the genome
consists of a circular
chromosome located in a
nucleoid region
• Some have smaller rings of
DNA called plasmids
• Plasmids w/ short codes of
DNA that may be beneficial
to bacteria (Ex. some code
for antibiotic resistance)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Genome
• Sex pili are longer than fimbriae and allow
prokaryotes to exchange DNA
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Plasmid F factor
• Cells containing the F plasmid function as
DNA donors during a process called
conjugation
• Cells without the F factor function as DNA
recipients during conjugation
• The F factor is transferable during conjugation
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Plasmid F factor
F plasmid
Bacterial chromosome
F+ cell
Mating
bridge
F– cell
Bacterial
chromosome
(a) Conjugation and transfer of an F plasmid
Plasmid F factor
F plasmid
Bacterial chromosome
F+ cell
Mating
bridge
F– cell
Bacterial
chromosome
(a) Conjugation and transfer of an F plasmid
Plasmid F factor
F plasmid
Bacterial chromosome
F+ cell
F+ cell
Mating
bridge
F– cell
Bacterial
chromosome
(a) Conjugation and transfer of an F plasmid
F+ cell
R Plasmids and Antibiotic Resistance
• R plasmids carry genes for antibiotic
resistance
• Antibiotics select for bacteria with genes that
are resistant to the antibiotics
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Reproduction and Adaptation
• Quick reproduction by binary fission
• every 1–3 hours
• Beneficial mutations can accumulate rapidly in
a population, allowing for rapid evolution
• ex. Antibiotic resistant strains are becoming
more common
• Many form inactive endospores
• to remain viable in harsh conditions
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Endospore
0.3 µm
Genetic Recombination
• DNA from different individuals can be brought
together by conjugation, transformation,
transduction
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Transformation and Transduction
• A prokaryotic cell can take up and incorporate
foreign DNA from the surrounding environment
in a process called transformation
• Transduction is the movement of genes
between bacteria by vectors like
bacteriophages (viruses that infect bacteria)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Phage DNA
A+ B+
A+ B+
Donor
cell
Phage DNA
A+ B+
A+ B+
Donor
cell
A+
Phage DNA
A+ B+
A+ B+
Donor
cell
A+
Recombination
A+
A– B–
Recipient
cell
Phage DNA
A+ B+
A+ B+
Donor
cell
A+
Recombination
A+
A– B–
Recipient
cell
A+ B–
Recombinant cell
Pathogenic Prokaryotes
• Prokaryotes cause about half of all human
diseases
• Lyme disease is an example
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5 µm
Fig. 27-21a
Deer tick
Fig. 27-21c
Lyme disease rash
Pathogenic Prokaryotes
• Bacteria typically cause disease by releasing
exotoxins or endotoxins
• Exotoxins cause disease even if the
prokaryotes that produce them are not present
• Endotoxins are released only when bacteria
die and their cell walls break down
• Many pathogenic bacteria are potential
weapons of bioterrorism
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings