Transcript viruses powerpoint 2013

VIRUSES
I. Structure
A. Viruses are
particles
containing:
1. Nucleic acid
2. Protein coat
B. They can reproduce only by infecting living
cells!
All viruses enter living cells and use the
infected cell to produce more viruses.
C. A capsid is the virus’s protein coat
D. Special proteins on the capsid “trick” the host
cell to let the virus in
Inside, virus genes get transcribed and
translated into more viruses
Host cell
then
bursts
and is
destroyed
II. Types of Viruses
• DNA viruses contain DNA nucleic acid
• More stable and less prone to mutation
• Respond well to vaccination
• Ex: smallpox, chicken pox, herpes, HPV,
Hepatitis B
• RNA viruses contain RNA nucleic acid
• Prone to mutations
• Require frequent vaccination
• Ex: Influenza, H1N1, Hepatitis C, HIV,
Rabies, Rotavirus, Yellow Fever
Examples of Viral Disease
• Smallpox, the common cold,
chickenpox, influenza, shingles,
herpes, polio, rabies, ebola, hanta
fever, and AIDS
Different Hosts
• Host cell is very specific
• Animal hosts: rabies, HIV, chicken pox
• Plant hosts: tobacco mosaic virus,
carnation vein mottle potyvirus
C. Viruses that infect
bacteria are called
bacteriophages
III. Lytic Cycle
1) Virus injects nucleic acid
into cell, taking over its
metabolism
2) Virus proteins and
nucleic acids assemble
into complete viruses
3) Virus enzyme breaks cell
membrane and wall, releasing
new viruses that attack other
Lysogenic Cycle
1. Virus injects its DNA into host cell
2. Viral DNA integrates into the host DNA
3. A host cell makes copies of the virus
ever time it divides.
The viral DNA embedded in the host’s
DNA is called a prophage.
V. Retroviruses
A. Retroviruses contain RNA.
Make a DNA copy FROM their RNA.
Then this DNA is inserted into the DNA of the host
cell.
B. HIV (human immunodefiniciency virus) can lead to
C. AIDS (acquired immunodefiniciency syndrome)
VI. Defense
A. Vaccination offers protection for uninfected
individuals
– Work by stimulating production of antibody forms
memory cells without causing disease
• Vaccines are made from killed or
weakened strains that cause antibody
production but not the disease
B. What are antibodies?
• Proteins that recognize invaders and block
their effects
• Flags invaders for death by white blood cells
Are Viruses Living or Non-living?
• They depend on
living things
• Most likely
developed after
living cells
• First viruses may have evolved from
genetic material of living cells
• Cannot reproduce on their own