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Bacteria. Staphylococcus bacteria in nose. Structure. Unicellular Some species form colonies 0.5–10 µ m, much smaller than the 10–100 µ m of many eukaryotic cells Most common shapes: spheres (cocci) rods (bacilli) and spirals. Bacterial Cell Wall. maintains cell shape - PowerPoint PPT Presentation
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Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
BacteriaStaphylococcus bacteria in nose
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Bacterial Cell Wall
• maintains cell shape
• provides physical protection,
• prevents the cell from bursting in a hypotonic environment
• Bacterial cell walls contain peptidoglycan, a network of sugar polymers cross-linked by polypeptides (proteins)
sugar
sugar
polypeptide
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• 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
• Many antibiotics target peptidoglycan and damage bacterial cell walls
Gram Stain Classification
Gram +Gram -
Cellwall
Peptidoglycanlayer
Plasma membrane
Protein
(a) Gram-positive: peptidoglycan traps crystal violet.
Cellwall Peptidoglycan
layerPlasma membrane
Protein
(b) Gram-negative: crystal violet is easily rinsed away, revealing red dye.
Outermembrane
Carbohydrate portionof lipopolysaccharide
Gram-positivebacteria
Gram-negativebacteria
20 µm
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• A polysaccharide or protein layer called a capsule covers many bacteria
Structure
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Bacterial Motility
• Most motile bacteria use flagella to propel themselves
• Many exhibit taxis, the ability to move toward or away from certain stimuli
Video: Prokaryotic Flagella (Video: Prokaryotic Flagella (Salmonella typhimuriumSalmonella typhimurium))
Flagellum
Filament
Hook
Basal apparatus
Cell wall
Plasmamembrane
50 nm
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fimbriae (also called attachment pili)
• allows them to stick to their substrate or other individuals in a colony
Fimbriae
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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
(a) Aerobic prokaryote (b) Photosynthetic prokaryote
Thylakoidmembranes
Respiratorymembrane
0.2 µm 1 µm
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• 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)
Genome
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• Sex pili are longer than fimbriae and allow prokaryotes to exchange DNA
Genome
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• 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
Plasmid F factor
F plasmid
F+ cell
F– cell
Matingbridge
Bacterial chromosome
Bacterialchromosome
(a) Conjugation and transfer of an F plasmid
Plasmid F factor
F plasmid
F+ cell
F– cell
Matingbridge
Bacterial chromosome
Bacterialchromosome
(a) Conjugation and transfer of an F plasmid
Plasmid F factor
F plasmid
F+ cell
F– cell
Matingbridge
Bacterial chromosome
Bacterialchromosome
(a) Conjugation and transfer of an F plasmid
F+ cell
F+ cell
Plasmid F factor
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• R plasmids carry genes for antibiotic resistance
• Antibiotics select for bacteria with genes that are resistant to the antibiotics
R Plasmids and Antibiotic Resistance
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
Endospore
0.3 µm
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Genetic Recombination
• DNA from different individuals can be brought together by conjugation, transformation, transduction
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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)
Donorcell
A+ B+
A+ B+
Phage DNA
A+
Donorcell
A+ B+
A+ B+
Phage DNA
Recipientcell
B–
A+
A–
Recombination
A+
Donorcell
A+ B+
A+ B+
Phage DNA
Recombinant cell
Recipientcell
A+ B–
B–
A+
A–
Recombination
A+
Donorcell
A+ B+
A+ B+
Phage DNA
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Pathogenic Prokaryotes
• Prokaryotes cause about half of all human diseases
• Lyme disease is an example
5 µm
Fig. 27-21a
Deer tick
Fig. 27-21c
Lyme disease rash
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• 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
Pathogenic Prokaryotes
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