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A virus must replicate with in
a host cell.
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The virus provides the ______ or ______ to replicate, and the host cells provide the _______ and _______.
RNA; DNA; energy; resources
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Viruses contain RNA __ DNA
or; not both
RNA viruses also contain code for reverse transcriptase, enzyme which makes DNA from RNA.
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Viral Structure contains
Nucleic acid (RNA or DNA)
Capsid
Envelope
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Capsid is
a protective coat enveloping the nucleic acid.
Determines the shape of the virus.
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Capsids are composed of individual protein subunits called
Capsomeres
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Capsids can be helical, ________, or in some cases ______-________. The combined capsid/nucleic acid arrangement is called the __________.
polyhedral (multi-sided); bullet-shaped; nucleocapsid.
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Envelope are
are external to the capsid, and are acquired from the combinations of proteins, lipids, and carbohydrates found in the membrane of the host cell.
present in some viruses.
- may have glycoprotein spikes.
- - determine host cell specificity.
- - may hide virus from host's immune system.
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What are the five step replication cycle?
- 1. Adsorption
- 2. Penetration
- 3. Synthesis
- 4. Maturation
- 5. Release
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What happens in the Adsorption step?
Attachment of the virus to the host cell.
Naked (non-enveloped) viruses attach to specific molecular sites on the cell surface.
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What happens in the Penetration cycle?
Virus enters the host cell through endocytosis or fusion and uncoats (takes off its envelope and capsid)
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What happens in the Synthesis step?
This process produces new genetic material and varies between the RNA and DNA viruses.
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What happens in the Maturation step?
is the assembly, or "packaging" of the newly synthesized molecules into complete virons.
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What happens in the Release step?
Departure of new virons from host cell.
Host cell may rupture or Host cell remains intact and releases the virus.
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There are several types of viral infections that fall into two main categories. What are the categories?
Acute Infections
Latent/Persistent Infections
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Acute infections
Disease cycle is relatively short.
Host cell ruptures and virus spreads to neighboring cells. (common cold (rhinovirus), influenza (types A and B), some hepatitis viruses).
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Latent/Persistent Infections
Virus becomes relatively inactive but reemerges.
Provirus remains in host cell and replicates new virions when "triggered" by some external event such as stress, fever, or other factors.
Herpes virus, Epstein-Barr virus, Human Immunodeficiency virus (HIV), Cold sores
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Immune System Viruses
Epstein-Barr, HIV
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Oncogenic Viruses
Possess oncognenes (cancer-causing genes) that cause uncontrolled and abnormal division of host cells by altering cell cycle "checkpoints".
Hepatitis B, Hepatitis C
Human Papilloma Virus
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Viruses such as the human papillomavirus have been directly linked to
cervical cancer in women.
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Treatment of Viral Infections:
Antibiotics are
ineffective.
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Treatment of Viral Infections:
Antiviral drugs
slow down attachment of virus to host cell
suppress, do not cure, viral infection.
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Treatment of Viral Infections:
Vaccines
Salk-Sabin (Polio)
Gardisil (Human Papilloma Virus-----> cervial cancer)
Hepatitis A, Heptovax (Hepatitis B)
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Substances produced by the host cell such as interferon
inhibit viral activity.
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