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Bacteria and Viruses
Chapter 19
19-1 Bacteria
• Common name for all prokaryotes
• unicellular organisms without a nucleus
• Were all in Monera
• Eubacteria
• live nearly everywhere
• normally protected by cell wall containing
peptidoglycan - cell membrane inside of cell wall
• Archaebacteria
•
•
•
•
lack peptidoglycan
DNA similar to eukaryotic DNA
most are extremophiles – live in harsh environments
methanogens; halophiles; extreme thermophiles
Prokaryotic Body Plan
DNA
capsule
bacterial flagellum
pilus
plasma
membrane
cell wall
ribosomes in
cytoplasm
cytoplasm
Identifying Prokaryotes
1. Shape
a. bacilli(us) – rod-shaped
b. cocci(us) – spherical
c. spirilla(us) – spiral and corkscrew shaped
2. Cell Walls
a. Gram-positive – have thick peptidoglycan cell
walls that take and hold stain
b. Gram-negative – thinner cell walls with lipids
on outside – does not hold stain
3. Movement
Metabolic Diversity
1. Chemoheterotrophs – must take in organic
molecules for energy and a supply of carbon
2. Photoheterotrophs – use photosynthesis for
energy, but take in organic compounds for
carbon source
3. Photoautotrophs – use photosynthesis for both
energy and carbon source
4. Chemoautotrophs – use chemosynthesis – get
energy from chemical reactions and use carbon
dioxide as carbon source
Releasing Energy
- bacteria release energy by cellular respiration and
fermentation
A. Obligate Aerobes
- require a constant supply of oxygen
B. Obligate Anaerobes
- must live in the absence of oxygen
C. Facultative Anaerobes
- can survive with or without oxygen
Growth and Reproduction
- under good conditions bacteria can reproduce
every 20 minutes
Binary Fission
- normal asexual reproduction of bacteria
- replicate DNA and then divide
Conjugation
- exchange of genetic material between bacterial
cells
- increases genetic diversity
Spore Formation
- allows survival of bad conditions for a long time
Prokaryotic Fission - 1
bacterial
chromosome
Bacterium before
DNA replication
DNA replication
begins
Figure 21.7
Page 350
Prokaryotic Fission - 2
parent DNA
molecule
DNA replication
completed
DNA copy
Membrane growth
moves DNA molecules
apart
Prokaryotic Fission - 3
New membrane and cellwall material deposited
Cytoplasm divided
in two
nicked plasmid
in donor cell
Conjugation
Transfer of plasmid
conjugation tube
to recipient cell
Importance of Bacteria
- while we usually think of bacteria negatively they
are actually essential to correct functioning in
ecosystems
A. Decomposers
- primary decomposers who make nutrients
available to plants
- used in sewage treatment plants also
B. Nitrogen Fixers
- Rhizobium in nodules of legume roots fix
nitrogen in a form the plants can use
C. Human Uses
• in food production
• in industry – can clean-up oil spills
• to synthesize drugs and chemicals
• genetic engineering now has them producing
human hormones
• Mutualism with Eschecaria coli in our colon where
they help us make vitamins
19-2 Viruses
- virus means “poison”
What is a Virus?
• non-living – no metabolism and can’t reproduce on
their own
• DNA or RNA core surrounded by a protein coat
• use a living cell’s internal structures to reproduce
themselves
• Capsid – protein coat - often with proteins on it
that help it invade a host cell – often highly specific
• once inside the host the viral genes get the host
cell to make viral proteins and DNA/RNA
- bacteriophage – a virus that attacks bacteria
Viral Infection
1. Lytic Infection
- virus enters a cell; has copies of itself made;
and causes cell to burst and release more
viruses
2. Lysogenic Infection
- virus enters a cell and has its DNA integrated
into the DNA of the host cell
- as cell replicates its DNA it also replicates the
viral DNA
- prophage – viral DNA embedded in host DNA
Lytic
Pathway
Lysis of host cell is induced;
infectious particles escape.
Tail fibers and other parts are
added to coats.
Virus particles bind to wall of suitable host. Viral
genetic material enters cell cytoplasm.
Viral protein molecules are assembled into
coats; DNA is packaged inside.
Viral DNA directs host
machinery to produce viral
proteins and viral DNA.
Stepped Art
Fig. 21.20 Page
Lysogenic
Pathway
Viral DNA usually becomes
integrated into the bacterial
chromosome.
Prior to prokaryotic fission, the
chromosome and integrated viral
DNA are replicated.
Viral DNA is excised from
chromosome and cell enters
lytic pathway.
After binary fission, each
daughter cell will have
recombinant DNA.
Stepped Art
Fig 21.20 (2)
- may stay inactive for a long time
- eventually something causes the DNA of the
prophage to be activated and it enters the
Lytic cycle and destroys the host cell
Retroviruses
• Viruses which have RNA as genetic material
• When they infect a cell the cell first makes DNA
from RNA template (reverse transcription)
• DNA inserts into cell’s DNA and can stay dormant
• Can cause some cancers, HIV causes AIDS, colds
(Copy Figure 19-11)
19-3 Diseases Caused by Bacteria and Viruses
While most bacteria and viruses are not harmful a
few are pathogens (disease causing)
- Disease results when a virus or bacteria interfere
with the host’s ability to get enough nutrients
or energy
- Louis Pasteur developed the Germ Theory of
Disease when he proved that bacteria can cause
disease
Bacteria cause disease by directly breaking down
cells for food or by releasing toxins that travel
throughout the body and interfere with normal
activity in the host.
- Vaccines are used to stimulate the immune system
by exposing it to a dead or weakened
pathogen.
- Antibiotics are used against bacterial infections
that the immune system doesn’t beat.
- Bacteria can be controlled by sterilization with
heat; disinfectants; and correct food processing
and handling.
Lyme Disease
Viral Disease
- Viruses produce disease by disrupting the body’s
normal equilibrium
- Most viruses are very specific in what cells they
attack – polio only attacks motor neurons
- Viral infections cannot be treated with antibiotics.