Viruses Where do viruses come from ? Bacteriophage Replication.
Viruses
description
Transcript of Viruses
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Viruses
Living or Not
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Virus• Virus – small
particle made of 1. Nucleic acids
either DNA or RNA
2. Surrounded by a protein coat
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Virus • Viruses are smaller than the tiniest bacterium.
• They are not considered to be alive:
1. Don’t grow or develop
2. Don’t carry on respiration
3. They can’t reproduce on their own
(Because they’re not alive, they cannot be “killed”. )
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Virus Structure
Capsid DNA
Attachment Protein
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Virus• The outer protein coat is called the capsid.
• This capsid gives the virus its shape.
• The protein arrangement determines what cell can be infected.
Attachment protein
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Virus • Every virus has a specially shaped device called an attachment protein
• These proteins anchor the virus to the cell
• Each virus can only attach to a specific kind of cell
• This can be an animal, plant, fungus, protist or bacteria cell
Attachment Protein
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Viral Replication Cycles• A virus must
infect a host cell to replicate.
• Once inside, the virus takes over the cell metabolism.
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Viral Replication Cycles• 2 ways for a virus
to enter a cell.
1. Virus nucleic acid is injected into the cell.
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Viral Replication Cycles2. Virus is
surrounded by plasma membrane and taken into the cell cytoplasm. This vacuole will burst releasing the virus.
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Lytic Cycle• Once inside, the
virus takes over the cell processes.
• The cell enzymes and energy are used to make more virus.
• The cell will burst releasing the viruses.
• Lysis – bursting of a cell.
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Lytic Cycle• The new viruses
infect more cells.• This active
process of making more viruses is called a lytic cycle
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Lysogenic Cycle• Lysogenic cycle – replication cycle
where the viral nucleic acid is incorporated in the cell DNA.
• This new DNA is called a provirus
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Lysogenic Cycle• The cell carries out its own functions. • Every time the cell replicates, it copies
the viral DNA.• This resting phase can last for many
years.
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Lysogenic cycle
• At any time, the provirus can be activated and enter a lytic cycle.
• When this happens, the virus will replicate and kill the cell.
• Examples: Herpes simplex I Hepatitis B Chicken pox
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Retrovirus• Retrovirus – a
virus with RNA as its nucleic acid.
• A retrovirus produces a DNA copy of its RNA
• It must work backwards making DNA from RNA
• HIV is a retrovirus
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Vaccines• Viruses cannot be
“killed” with antibiotics.
• They are controlled by vaccines.
• Vaccine- weakened form of a virus used to produce an immune response.
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Illnesses caused by viruses
• Cold• Flu • Chicken Pox• Measles • Mumps• Polio• HIV Aids
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BREAKING NEWS !• Papiloma virus
causes cancer!!!• HPV(human
papiloma virus) has been shown to cause cervical cancer
• Other viruses are being studied as possible causes of cancer.(that means tumors)
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Spreading Disease• Disease causing
agents like viruses and bacteria are easily spread from person to person.
• Typhoid Mary was a cook who infected 53 people with the bacterial disease typhoid fever.