1. The Prokaryotes
Chapter 16

2. Virus
Bacterium
Animal
cell
Animal cell nucleus
0.25 µm

3. 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

4. Pili
Nucleoid
Ribosomes
Plasma
membrane
Cell wall
Bacterial
chromosome
Capsule
0.5 µm
Flagella
A typical
rod-shaped
bacterium
A thin section through the
bacterium Bacillus
coagulans (TEM)

5. 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

6. Prokaryotic Classification
Domain Bacteria vs Archaea
Cell Wall composition
Gram negative or gram positive
Cell shape
Mode of nutrition
Molecular characteristics
rRNA sequence comparisons

7. 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

8. Gram-Positive
Extra thick peptidoglycan layer allows cells to RETAIN primary stain and thus appear BLUE
Bacillus anthracis

9. Gram Negative
Do NOT retain primary stain and thus take in the PINK counterstain
Most PATHOGENIC bacteria
are Gram-Negative!!

10. Additional Features of Prokaryotic Cells
Capsule
Tonsil cell
Bacterium
Some Prokaryotes also may exhibit:
Capsules
a sticky layer of polysaccharides or protein.
shields pathogenic prokaryotes from attacks by a host’s immune system.
Fimbriae
Hairlike projections enable prokaryotes to stick to their substrate or each other
Flagella
help prokaryotes move in their environment
Produce endospores
Allow bacteria to remain dormant during harsh conditions
Endospore
Flagella
Fimbriae

11. Bacterial Metabolism
Extremely diverse methods of obtaining energy and nutrients
ENERGY SOURCE
Sunlight
Chemicals
Photoautotrophs
Chemoautotrophs
CO2
Oscilliatoria
Unidentified “rock-eating” bacteria
CARBON SOURCE
Photoheterotrophs
Chemoheterotrophs
Organic compounds
Rhodopseudomonas
A Bdellovibrio attacking a
larger cell

12. Roles of Bacteria in Ecosystems and Human 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

13. 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!!!

14. 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