2. GENERAL CHARACTERISTICS OF VIRUSES
Virus is the Latin word for
“poison”
1935
Wendell Stanley isolated
the Tobacco Mosaic virus
for the first time
3. DEFINITION OF LIFE
A complex set of processes resulting from the actions of proteins
specified by nucleic acids
“Viruses are not living things. Viruses are complicated assemblies of
molecules, including proteins, nucleic acids, lipids, and
carbohydrates, but on their own they can do nothing until they enter
a living cell. Without cells, viruses would not be able to multiply.
Therefore, viruses are not living things.”
4. Viruses are “alive” (able to multiply) when they
enter a host organism
We will say that viruses are living, but they are not.
6. FEATURES OF VIRUSES
Only one type of nucleic acid
DNA or RNA (not both)
A protein coat
Made of lipids, carbohydrates, proteins
7. • Must have a host cell
• Uses the cells machinery to copy itself
• Makes specialized structures that can
transfer the viral information to other cells
• Lack personal enzymes
• http://www.youtube.com/watch?v=sHThHRV4uo
9. HOST RANGE
Viruses can have a host range
A spectrum of host cells the virus can infect
Viruses that infect bacteria are bacteriophages
(phages)
Outer surface of virus must chemically interact with
specific receptor site on host cell
10. VIRAL SIZE
Viruses are very small compared to bacterial cells
Need an electron scanning microscope to view
11. VIRAL STRUCTURE
Virion = complete, fully developed, infectious viral particle
composed of nucleic acid and surrounded by a protein
coast that protects it from the environment
12. NUCLEIC ACID
Prokaryotes and Eukaryotes use RNA and DNA as
genetic information
Viruses use RNA or DNA-not both
It is single or double stranded
13. CAPSID AND ENVELOPE
Protein coat = capsid
Combination of lipid,
proteins, and carbohydrates
that convers the capsid =
envelope
Capsids without envelopes =
nonenveloped viruses
14. When a virus enters a host cell, the host antibodies are produced
An interaction between antibodies and virus’ should inactivate the
virus
Some viruses escape antibodies and are able to change their surface
proteins
Surface proteins are called spikes
This is why you can get the flu many different times
15. GENERAL MORPHOLOGY
Compare with prokaryotic morphology
Helical : long rods, hollow and cylindrical spirals
Polyhedral : many sided viruses
Complex : complicated structure
Many bacteriophages
16. TAXONOMY OF VIRUSES
A viral species is a
group of viruses sharing
the same genetic
information and
ecological niche.
17. GROWING VIRUSES
Nonliving: needs
a host cell
Difficult and
expensive to
maintain cultures
Usually learn
from
bacteriophages
plaque = clearing
within a media
20. BACTERIOPHAGES
LYTIC CYCLE
1. attachment to receptor site
2. injects DNA/RNA into cell
3. host cell starts making viral
copies of nucleic acid
4. bacteriophages are assembled
inside host cell
5. host cell is lysed
LYSOGENIC CYLE
Process where cell is not
lysed and is able to stay
alive
22. VIRUSES AND CANCER
Almost anything that can alter the genetic material of a
eukaryotic cell has the potential to make a normal cell
cancerous
HPV
Hepatitis B
Leukemia, Feline leukemia
23. VIRUSES AND INFECTIONS
Latent infection = infection capable of
staying dormant until stimulus is applied
Chronic viral infection = long lasting viral
infection that occurs over a gradual time
period (usually fatal)
HerpesFever blisters/cold sores
Chicken poxshingles
24. PRIONS
????????
A prion is a proteinaceous infectious particle
A protein that infects like a virus
These diseases run in families; however, they can’t be totally inherited
There is a lot that is not known about prions
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Mad Cow disease
Kuru
Creutzfeldt-Jakob disease
Fatal familial insomnia
Gerstmann-Straussler-Scheinker
syndrome
25. VIROIDS
Viroids are short pieces of RNA with no protein
coat that does not code for any protein
They cause plant diseases
Much is still to be learned about these particles
