1 Review In what ways do prokaryotes differ from
one another
Evaluate Use pg 486. Which category of prokaryote
is the most flexible in the energy sources it can
use- explain
2 Review List three ecological roles played by
prokaryotes
Explain Why are nitrogen fixing bacteria so
important
CH 20 VIRUSES AND PROKARYOTES
20.2 Prokaryotes
Classifying Prokaryotes

Prokaryotes
 Unicellular
organisms
that lack a nucleus
 Has DNA, but it is not
found in a membranebound nuclear envelope.

Prokaryotes are classified as Bacteria or Archaea
 Two
of the three domains of life.
Bacteria



Larger of the two groups
Do not agree exactly how many phyla
Live almost everywhere.

Surrounded by a cell wall that
protects the cell from injury
and determines its shape
 Contains


peptidoglycan
Some have flagella
Pili
 Serve
mainly to anchor the
bacterium to a surface or to
other bacteria.
Archaea


Look very similar to bacteria
But
 Walls
of archaea lack peptidoglycan
 Membranes contain different lipids
 DNA sequences of key archaea genes are more like
those of eukaryotes than those of bacteria
 Live in extremely harsh environments.
Three Archae Varieties
1.
Thermoacidophiles

Live in hot and acid environments such as hot springs
and coal debris, still keep internal pH around 7.
Three Archae Varieties
2. Halophiles


Live in high salt concentrations
Ocean borders, great salt lake, dead sea.
Three Archae Varieties
3. Methanogens



Produce methane
Anaerobic
Live in thick mud and the digestive tracts of animals.
Size, Shape, and Movement

Bacilli
 Rod-shaped

Cocci
 Spherical


prokaryotes.
Spirilla
 Spiral

prokaryotes.
and corkscrew-shaped prokaryotes
Also be distinguished by whether they move and
how they move
1-5 micrometers.
Nutrition and Metabolism


Store energy as sugars
Energy is released during cellular respiration,
fermentation, or both.
Energy Capture

Page 486.
Energy Release

Page 487.
Growth and Reproduction

Binary fission
 Replicates
its DNA and divides in half, producing two
identical cells
 Asexual
 Does not involve the exchange or recombination of
genetic information
 With optimal conditions can replicate every 20 minutes

Endospore
 Thick
internal wall that encloses the DNA and a portion
of the cytoplasm during unfavorable conditions.
Mutation


Mutations are one of the main ways prokaryotes
evolve
Mutations are inherited by daughter cells
produced by binary fission.
Conjugation



Exchange of genetic
information in prokaryotes
Hollow bridge forms between
two bacterial cells
Genetic material, usually a
plasmid, moves from one cell
to the other.
The Importance of Prokaryotes

Essential in maintaining every aspect of the
ecological balance of the living world.
Decomposers

Decompose complex organic molecules into
simpler molecules
 Supply
raw materials
 Treat industrial sewage
 Purify water
 Produce fertilizer.
Producers


Among the most important producers
Many food chains dependant on them.
Nitrogen Fixers



Nitrogen in atmosphere is not useable by the
majority of species
Nitrogen-fixing bacteria and archaea provide 90
percent of the nitrogen used by other organisms
Legumes
 Symbiotic
relationship between plants and nitrogen
fixing bacteria that live in nodules in the plant’s roots.
Human Uses of Prokaryotes



Yogurt, sauerkraut, and buttermilk
Digest petroleum and remove human-made waste
from water
Synthesize drugs and chemicals.