Transcript 18.1 Studying Viruses and Prokaryotes

18.1 Studying Viruses and Prokaryotes
Characteristics of Living Organisms
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Made up of cell(s)
Reproduce on their own
Have genetic information, DNA
Grow and Develop
Obtain and use materials and energy (metabolism)
Maintain and internal balance (homeostasis)
Respond to their environment
Evolve, change over time
18.1 Studying Viruses and Prokaryotes
Viruses, bacteria, viroids, and prions can all cause
infection.
• Any disease-causing agent is called a pathogen.
1 nanometer (nm) = one
billionth of a meter
100 nm
eukaryotics cells
10,000-100,000 nm
viruses
50-200 nm
prokaryotics cells
200-10,000 nm
viroids
5-150 nm
prion
2-10 nm
18.1 Studying Viruses and Prokaryotes
What is the difference between bacteria and viruses?
• A virus is made of DNA or RNA and a protein coat.
– non-living pathogen
– can infect many
organisms
• Bacteria are onecelled microorganisms
that can cause
infection.
– living pathogen
18.1 Studying Viruses and Prokaryotes
Viruses differ in shape and in ways of entering host
cells.
• Viruses have a simple structure.
– genetic material (DNA or RNA)
– Capsid (a protein shell)
– maybe a lipid envelope, a protective outer coat
enveloped
(influenza)
capsid
nucleic acid
lipid
envelope
helical
(rabies)
Surface proteins
capsid
nucleic acid
surface
proteins
lipid envelope
polyhedral
(foot-and-mouth
disease)
surface
proteins
capsid
nucleic acid
18.1 Studying Viruses and Prokaryotes
• Viruses enter cells in various ways.
– bacteriophages pierce host cells
colored SEM; magnifications:
large photo 25,000; inset 38,000x
18.1 Studying Viruses and Prokaryotes
• Viruses enter cells in various ways.
– viruses of eukaryotes enter by endocytosis
18.1 Studying Viruses and Prokaryotes
They are simply packaged sets of genes that move from
one host cell to another.
The different viral shapes, play a role in how viruses work.
• It is how they identify their host cell.
enveloped
(influenza)
capsid
nucleic acid
lipid
envelope
helical
(rabies)
Surface proteins
capsid
nucleic acid
surface
proteins
lipid envelope
polyhedral
(foot-and-mouth
disease)
surface
proteins
capsid
nucleic acid
18.1 Studying Viruses and Prokaryotes
Enveloped Virus
• Ex: influenza
18.1 Studying Viruses and Prokaryotes
Helical virus
• Example: Rabies
18.1 Studying Viruses and Prokaryotes
18.1 Studying Viruses and Prokaryotes
Polyhedral Virus
• Example: Foot and mouth (coxsackie virus)
18.1 Studying Viruses and Prokaryotes
18.1 Studying Viruses and Prokaryotes
Viruses are specific in what they infect
• Most viruses are species specific
– Ex. Small pox-humans only, tobacco mosaic virusplants only, bacteriophages-bacteria only
• can only affect a limited range of hosts
– host range is determined by the specificity of
attachment to the cells, which depends on properties
of both the virion's coat and specific receptors on the
cell surface
• Some can affect a number of species with in mammals
ex. Rabies
18.1 Studying Viruses and Prokaryotes
The genetic material in viruses differ from prokaryotes and
eukaryotes.
• They can have either DNA or RNA, but never both.
enveloped
(influenza)
capsid
nucleic acid
lipid
envelope
helical
(rabies)
Surface proteins
capsid
nucleic acid
surface
proteins
lipid envelope
polyhedral
(foot-and-mouth
disease)
surface
proteins
capsid
nucleic acid
18.1 Studying Viruses and Prokaryotes
• A prion is made only of proteins.
– causes misfolding of other proteins
– results in diseases of the brain
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Alzheimer's disease
Creutzfeldt-Jakob disease (mad cow disease)
Down's syndrome
Fatal familial insomnia
Kuru Leprosy
18.1 Studying Viruses and Prokaryotes
• A viroid is made only
of single-stranded
RNA.
– causes disease in
plants
– passed through
seeds or pollen
Tobacco mosaic virus
18.1 Studying Viruses and Prokaryotes
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Viruses can only reproduce after they have infected
host cells.
HIV leaving
host cell
18.1 Studying Viruses and Prokaryotes
• Bacteriophages infect bacteria.
The T-4 Bacteriophage virus is
about to attack the bacterium.
The virus injects its
genetic material into the
bacterium.
The bacterium explodes after it is forced to make copies of the
virus!
18.1 Studying Viruses and Prokaryotes
Several viruses have been linked to certain types of
cancer:
• The Epstein-Barr virus has been linked with Burkitt's lymphoma.
• The Hepatitis B and C viruses have been linked with liver cancer in
people with chronic infections.
• HTLV-I, a retrovirus, has been linked to T-cell leukemia.
• Papilloma viruses have been linked with cervical cancer.
18.1 Studying Viruses and Prokaryotes
Lytic infection
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1. Bacteriophage injects DNA into cell
2. Viral DNA forms plasmid in host
3. May enter lysogenic cycle
4. Host makes new virus
Final: Host explodes (lyses), spreading virus
18.1 Studying Viruses and Prokaryotes
Lytic infection causes the cell to burst.
host bacterium
The bacterophage attaches
and injects it DNA into a host
bacterium.
The host bacterium breaks apart,
or lyses. Bacteriophages are able
to infect new host cells.
The viral DNA
forms a circle
(plasmid).
The viral DNA directs the host
cell to produce new viral parts.
The parts assemble into new
bacteriophages.
The virus may enter the
lysogenic cycle, in which the
host cell is not destroyed.
18.1 Studying Viruses and Prokaryotes
Lysogenic Cycle
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1. Bacteriophage injects DNA into cell
2. Viral DNA forms prophage (part of host DNA)
3. Viral DNA replicates with host
4. Cell reproduces producing many copies of virus
Final: Cell has dormant virus or may enter lytic cycle
18.1 Studying Viruses and Prokaryotes
• A lysogenic infection does no immediate harm.
The prophage may leave the
host’s DNA and enter the
lytic cycle.
The viral DNA is called a prophage
when it combines with
the host cell’s DNA.
Many cell divisions produce a
colony of bacteria infected
with prophage.
Although the prophage is not
active, it replicates along with
the host cell’s DNA.
18.1 Studying Viruses and Prokaryotes
Viruses cause many infectious diseases
– HIV
– Retrovirus
destroys white
blood cells
– Causes AIDS
HIV-infected
white
blood cell
18.1 Studying Viruses and Prokaryotes
Vaccines are made from weakened pathogens.
• A vaccine stimulates body’s immune system to prepare
for attack from microbes
18.1 Studying Viruses and Prokaryotes
Vaccines
• Characteristics: Made
of weakened virus or
parts of virus
Body’s immune system
allowed to recognize
and build antibodies