Transcript Viruses and Prokaryotes

The Prokaryotes
Chapter 16
Virus
Bacterium
Animal
cell
Animal cell nucleus
0.25 µm
Comparing Prokaryotic and Eukaryotic Cells
• Unicellular
• Prokaryotic cells have no nucleus
– In a prokaryotic cell, DNA is in an unbound region called
the nucleoid
– Prokaryotic cells lack membrane-bound organelles
• Cell Wall surrounds plasma membrane
Pili
Nucleoid
Ribosomes
Plasma
membrane
Bacterial
chromosome
Cell wall
Capsule
0.5 µm
Flagella
A typical
rod-shaped
bacterium
A thin section through the
bacterium Bacillus
coagulans (TEM)
Bacterial Exhibit Asexual Reproduction by
Binary Fission
• Bacteria have single, circular chromosome
• Many bacteria also have plasmids
– smaller circular DNA molecules that can replicate independently
of the chromosome
• Bacterial cells divide by binary fission
• Genetic variation mainly by mutations
– Since bacteria can reproduce rapidly, new mutations
quickly increase genetic diversity
Prokaryotic Classification
• Domain Bacteria vs Archaea
• Cell Wall composition
– Gram negative or gram positive
• Cell shape
• Mode of nutrition
• Molecular characteristics
– rRNA sequence comparisons
Composition of Cell Wall: Gram-positive vs
Gram-negative bacteria
•
•
•
Cell Wall surrounds plasma
membrane
– Composed of lipids,
carbohydrates and protein
• Peptidoglycan (mix of
protein and
carbohydrates)
– NO Cellulose (plants cells)
– Provides structure and
support
Structure of cell wall categorize
bacteria based on ability to retain
the Gram stain
Series of two staining procedures
– Crystal violet + iodine
– Ethanol rinse
– Safranin counterstain
Gram-Positive
• Extra thick peptidoglycan layer allows cells to RETAIN
primary stain and thus appear BLUE
Bacillus anthracis
Gram Negative
•
Do NOT retain primary stain and thus take in the PINK counterstain
•
Most PATHOGENIC bacteria
are Gram-Negative!!
Additional Features of Prokaryotic Cells
Some Prokaryotes also may exhibit:
• Capsules
– a sticky layer of polysaccharides or
protein.
• shields pathogenic
prokaryotes from attacks by a
host’s immune system.
•
•
•
Capsule
Tonsil cell
Fimbriae
– Hairlike projections enable
prokaryotes to stick to their
substrate or each other
Bacterium
Endospore
Flagella
– help prokaryotes move in their
environment
Flagella
Produce endospores
– Allow bacteria to remain dormant
during harsh conditions
Fimbriae
Bacterial Metabolism
• Extremely diverse methods of obtaining energy and nutrients
Sunlight
Photoautotrophs
Chemicals
Chemoautotrophs
Oscilliatoria
Unidentified “rock-eating” bacteria
Photoheterotrophs
Chemoheterotrophs
Rhodopseudomonas
A Bdellovibrio attacking a
larger cell
CO2
Organic compounds
CARBON SOURCE
ENERGY SOURCE
•
Roles of Bacteria in Ecosystems and Human
Ecosystems
Health
– Decomposers
• Recycle nutrients that would otherwise
remain unavailable in dead organisms and
waste
– Producers
• Important primary producers in oceans and
lakes
•
Human Health
– Source of antibiotics
– Aid in digestion and vitamin synthesis
•
Disease
•
Fermented foods
– Yogurt
– Cheese
– Soy sauce
Cyanobacteria
• Photosynthesize similar to plants
– First to introduce oxygen to atmosphere of early Earth
• Unicellular or colonial
• Many fix N2 - only require water CO2, N2 to grow!!!
Domain Archaea: Structure and Function
• Plasma membranes contain unusual lipids
– Glycerol linked to branched-chain hydrocarbons rather than
fatty acids
• No peptidoglycan in cell walls
• Unique habitats and metabolism
• Extreme halophiles thrive in very salty places.
• Extreme thermophiles thrive in
– very hot water, such as geysers, and
– acid pools.
• Methanogens
– live in anaerobic environments,
– give off methane as a waste product from