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Chapter 19
Bacteria and
Viruses
I. Prokaryotes
A. Prokaryotes: single-celled
organisms that lack a nucleus
1. Eubacteria – walls contain
peptidoglycan (a carbohydrate)
2. Archaebacteria – lack
peptidoglycan, DNA similar to
eukaryotes
B. Identifying Prokaryotes
1. Shapes
a. Bacilli (rod shaped)
b. Cocci (spherical)
c. Spirilla (spiral)
2. Cell Walls
a. Gram-positive (with peptidoglycan)
– purple
b. Gram-negative (without
peptidoglycan) – red
Which bacteria is rod shaped and has
peptidoglycan in its cell walls?
NO….why?
This one?
This
Yes!
one?
NO…it
This
hasone?
spheres!
NO…it
This
hasone?
spheres!
3. Arrangement
a. Staphyl: Clumps or clusters
b. Strepto: long chains
4. Movement
a. Propelled by tail-like structure called
flagella
b. Glide along a slime secretion
c. Move along like snakes
d. Some do not move
C. Obtaining Energy
1. Autotrophs
a. Photoautotrophs: obtain energy
from photosynthesis
b. Chemoautotrophs: obtain energy
from inorganic molecules
2. Heterotrophs
a. Can cause food poisoning
b. Photoheterotrophs: photosynthetic,
but also need organic compounds
for nutrition
D. Releasing Energy
1. Obligate aerobes: require oxygen
2. Obligate anaerobes: cannot live in
presence of oxygen
3. Facultative anaerobes: do not need
oxygen, but can live in the presence
of it
E. Growth and Reproduction
1. Binary fission: cell divides, asexual
2. Conjugation: transfer of genetic
information from one cell to another,
sexual
3. In unfavorable conditions, many
bacteria can form endospores – can
remain dormant for months or years
II. Bacteria in Nature
A. Decomposers
1. Help recycle nutrients – break down
dead organisms
2. Used in sewage treatment
B. Nitrogen Fixers
1. Nitrogen fixation: converting nitrogen
into a form plants can use
2. Rhizobium grow on roots of
soybeans and other legumes –
converts nitrogen to ammonia for
the
plant
The roots of the host plant
become infected with the
bacteria as seedlings, and
respond by surrounding the
bacteria with root hairs. The
relationship between a particular
host species and a particular
bacterium is highly specific, and
is regulated by a series of
recognition events that prevent
the wrong species of bacterium
from taking up residence in the
wrong plant.
Nitrogen-fixing bacteria
Rhizobium on the roots of the
broad bean plant Vicia faba.
C. Bacteria and Disease
1. Pathogen: disease-causing agents
2. 2 ways bacteria cause disease
a. Break down tissues for food
b. Release toxins
3. Many can be prevented with
vaccines; many can be treated with
antibiotics
D. Human Uses of Bacteria
1. Food – cheese, yogurt, buttermilk,
sour cream, pickles, sauerkraut
2. Industry – cleaning up oil spills,
mining minerals, synthesizing drugs
3. Bacteria live in our digestive tract to help
in digestion (called normal flora)
Billions of bacteria live in each of
us. If we could weigh all the
bacteria in the gastrointestinal tract,
it would amount to about three and
one-half pounds.
E. Controlling Bacteria
1. Sterilization: destroy bacteria by
subjecting them to great heat or
chemicals
a. Boiling, frying, steaming can all
kill bacteria
b. Disinfectant chemical solutions
can be used in homes and
hospitals
2. Refrigeration – bacteria grow slowly
at low temperatures
III. Viruses
A. Viruses: particles of nucleic acid and
protein
1. Nucleic acid = DNA or RNA that
contains instructions for making new
copies of the virus
2. Capsid: outer protein coat
B. Viral Infection
1. Infect cells and replicate inside host
cell
2. Bacteriophage: viruses that infect
bacteria
3. 2 types of viral infections
a. Lytic infection: virus enters cell,
make copies of itself and causes the
cell to burst
b. Lysogenic infection: virus embeds
its DNA into DNA of host and is
replicated with host cell’s DNA
C. Viruses and Disease
1. Many viruses can be prevented
through the use of vaccines (polio,
measles, influenza)
2. Oncogenic viruses cause cancer
3. Retroviruses contain RNA
4. Prions contain no DNA or RNA, only
protein
polio
Measles
Regulation of cell cycles is of key
importance in human papilloma
virus (HPV)-associated cervical
carcinogenesis
Retroviruses
HIV
Prions
Mad cow disease
QUIZ
Next class!