Lab 2 next week on Protists
(Chapter 28)
• There will be a short quiz on this week’s
material and next week’s lab handout
• Bring a pencil for drawing
• Bring the “Atlas”
• Bring your text if you can bear to.
• Overview: They’re (Almost) Everywhere!
• Prokaryotes are microscopic, unicellular,
numerous.
• 1 g of soil contains millions/billions of
prokaryote cells.
• There are more bacterial cells in your body
than human cells
• Prokaryotes are fantastically diverse –
genetically, ecologically, etc.
Chapter 27 -- Prokaryotes
A key to types of cells:
1 Cells internally complex, with nuclei and membrane-bound
organelles ……………………………………….. Eukaryotes
1’ Cells internally simple, lacking nuclei and membrane-bound
organelles …………………………………………Prokaryotes
• Prokaryotic cells have a variety of
shapes: spheres (cocci), rods (bacilli),
and spirals
1 μm
Figure 27.2a–c (a) Spherical (cocci)
2 μm
(b) Rod-shaped (bacilli)
5 μm
(c) Spiral
The capsule of many prokaryotes
surrounds the cell wall
• The prokaryote cell wall maintains cell
shape and provides physical protection.
• Prokaryote cell walls contain
polysaccharides and proteins.
• Cell walls are produced outside the cell
(plasma) membrane and are also found in
fungi, plants and “algae”.
1
Some prokaryotes have fimbriae
which facilitate attachment
• Some bacteria are motile, propel themselves by
flagella
• Taxis – movement toward or away from a stimulus
Flagellum
Filament
50 nm
Cell wall
Hook
Basal apparatus
Figure 27.6
Compartmentalization of function in
prokaryotes
• Respiration and photosynthesis may occur
on specialized membranes.
• Most of the DNA is in a single circular
“chromosome”.
• Some DNA may be in circular plasmids
Prokaryote metabolisms are
diverse ….
• Phototrophs use light as an energy source
• Chemotrophs use chemical compounds as
an energy source
• Autotrophs can use CO2 as their sole
source of carbon
• Heterotrophs need more complex
compounds as their source of carbon
Plasma
membrane
Reproduction and adaptation
• Prokaryotes reproduce rapidly by binary
fission.
• Conjugation results in horizontal gene
transfer.
• Prokaryotes evolve rapidly in response to
environmental challenges, e.g. antibiotics
… and here are the possibilities:
•
•
•
•
Photoautotrophs
Chemoautotrophs
Photoheterotrophs
Chemoheterotrophs
2
Phylogenetic classification of organisms
based on molecular (genetic) evidence
Eukaryotes
Domain
Eukarya
Nanoarchaeotes
Korarchaeotes
Gram-positive
bacteria
Cyanobacteria
Spirochetes
Chlamydias
Delta
Epsilon
Beta
Gamma
Alpha
Proteobacteria
Universal ancestor
Figure 27.12
Some biological roles of
prokaryotes
A Modern Classification of Life
• Domain Bacteria – prokaryotes, many well
known and familiar species.
• Domain Archaea – prokaryotes,
discovered recently, many inhabit extreme
environments.
• Domain Eukarya – eukaryotes (animals,
fungi, plants, “algae”, “protozoa”.
Domain
Archaea
Domain Bacteria
– on the basis of appearance, metabolism,
structure, response to stains, etc.
– or on the basis of their DNA or RNA. This
produces a phylogenetic (evolutionary)
classification
Crenarchaeotes
• Prokaryotes can be classified
Euryarchaeotes
Prokaryote classification
•
•
•
•
Decomposers
Nitrogen fixers
Symbionts
Pathogens
3