Download Chapter 19

Chapter 19
Bacteria and
Viruses
Prokaryotes: single-celled
organisms that lack a nucleus


Eubacteria
 walls contain peptidoglycan (a
carbohydrate found in cell walls of
eubacteria)
Archaebacteria: includes methanogens,
halophiles and thermophiles
 Lack peptidoglycan
 DNA sequences of key archaebacteria
genes are more like eukaryotes than
eubacteria.
Classifying prokaryotes
Done by shape
Reaction to Gram stain (due to nature of cell
wall)
Arrangement

Diplo = 2
Staphylo = cluster
Strepto = chain
Movement



Some non-motile
Some undulate like a snake
Others use flagella or secretions to move
Identifying Prokaryotes
1. Shapes
a. Bacilli (rod shaped)
b. Cocci (spherical)
c. Spirilla (spiral)
Reaction to Gram stain is due to nature of cell
walls
a. Gram-positive
(cell walls contain w/peptidoglycan)
– appear purple
b. Gram-negative
(cell walls lack
peptidoglycan –
appear red
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
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
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
Exponential Growth Curve
Uses of Bacteria
• Food – cheese, yogurt, buttermilk,
sour cream, pickles, sauerkraut
• Industry – cleaning up oil spills,
mining minerals, synthesizing drugs
(such as insulin and human growth
hormone)
• Assist in digestion
– symbiotic
relationship in our
digestive tract.
Bacteria in Nature
Decomposers
1. Help recycle nutrients – break down
dead organisms
2. Used in sewage treatment
Bacteria are important as
decomposers
Recycles important nutrients.
Bacteria in the Nitrogen Cycle
Nitrification – “fixing” N2
1. Nitrogen fixation:
converting nitrogen gas
into nitrate or ammonia
2. Example: Rhizoacter
which grow on roots of
soybeans and other
legumes. Reduces need
for application of fertilizer.
Bacteria also release nitrogen
back into the environment. Called (denitrification)
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
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, can be treated with
antibiotics
Cross-linkages holding cell wall
and cell membrane together do
not form properly.
Antibiotics
First discovered accidentally, Alexander Fleming
Work by interfering with cell wall production so bacterial
can’t reproduce.
Cross linkages cannot form so cell wall develops holes and
bacterium ruptures.
Some bacteria have antibiotic properties; ex: Streptomyces
Only bacteria … not viruses … can be killed with
Bacterium elongates
antibiotic treatment.
preparing to divide.
Then ruptures
when cell wall
fails.
PENICILLIN KILLING E. coli
Bacteria in Biotechnology
Transformation – Bacterial cells pick up
DNA from other sources (including dead
bacteria) and incorporate it into their own
genome. Increases genetic variety and
opportunities for resistance.
Transduction – Process of using a virus
to transfer DNA from one bacterial cell to
another.
PCR – insert gene into bacterial
plasmid for rapid replication of sample
Bacterial Diseases:
Necrotizing fasciitis
• Caused by a mutated
Streptococcus
• Reproduces rapidly
• Tissue must be
removed to stop spread
• Patient is put into a
pressure chamber
(forcing O2 into tissue to
assist healing) to
reduce the spread.
Anthrax
Direct contact
Many different strains
Found in lower vertebrates
– goats, sheep, cattle
Three types



Cutaneous – skin – death
rare if treated
Inhalation – Cold-like – fatal
Gastrointestinal – 25-60%
Bubonic Plague or Black Death
Caused by pathogenic
bacteria spread from
China on trade ships (13
Symptoms include
swollen lymph nodes
(buboes, hence the
name), high fever, and
delirium.
90% death rate
Killed 1/3 of the
population of Europe
within a 5 year period
1347-1352 (including
Shakespeare’s siblings)
Lyme Disease
• Transmitted by Deer tick.
Lyme Disease Symptoms
Botulism & E. Coli
• Botulism
•
•
•
Muscle-paralyzing
disease.
Food-borne
Anaerobic
• E. Coli
•
•
•
•
1,000 of strains
Undercooked meat
Sewage water
Lives in intestines without
causing a problem
VIRUSES
Non-living particles consisting of nucleic
acid (RNA or DNA) surrounded by a
protein coat
No organelles, no nucleus, etc.
Parasitic
Rely on a host for replication
Bacteriophage = virus that
infects bacteria
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
Bacteriophage:
virus that infect bacteria
Mechanism:
Fibers attach
Contractile
sheath
squeezes down
Nucleic acid
(DNA or RNA)
in head (capsid)
is injected into
bacterial host
Head/Capsid
Contractile
Sheath
Tail
Tail Fibers
Base Plate
In a viral infection, do people get
sick from the protein coat or the
DNA core?
Viral Infection Cycles
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
Virus Reproduction
The Lysogenic Cycle
Virus Reproduction
The Lytic Cycle
Viral Diseases
1. Common human diseases caused by a virus:
common cold (rhinovirus), chickenpox, measles,
mumps, polio, rabies, hepatitis
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
Human Viral Diseases: Ebola
Found in Primates
Animal-Borne Virus
RNA virus
Incubation – 2-21
days
Fever, headache,
joint & muscle pain –
rash red eyes –
Extensive bleeding
from all orifices.
SARS
Severe Acute Respiratory Syndrome
Hot Zone- China, Toronto
Symptoms – Flu like- fever,
headache, dry cough
Transmission- Person to
person contact, respiratory
secretion
Military action has been
taken to keep virus
controlled.
Small Pox
Humans are the
natural host.
Spread by face to
face contact. – Also
body fluids.
Most Contagious
during Early Rash
continues till the last
scab falls off.
HIV
Human Immune Deficiency Virus
Fastest Spreading
disease in Africa
Effects white blood
cells. T-Cells
AIDS diagnosed
when T-cell count
falls below 200
West Nile Virus
Host – Birds
Spread through mosquitoes
Fever, headache, and body
aches, occasionally with
skin rash and swollen
lymph nodes.
Rare encephalitis
1% of mosquitos carry the
virus, 1% of those infected
will die.
Viroids and prions
Viroids: tiny, naked
circular RNA that infect
plants; do not code for
proteins, but use cellular
enzymes to reproduce;
stunt plant growth
Prions: “infectious
proteins”; “mad cow
disease”; trigger chain
reaction conversions; a
transmissible protein