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24 Cards in this Set
- Front
- Back
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History of Viruses |
first virus discovered
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What are viruses
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Tiny, nonliving particules composed of nucleic acids enclosed in a protein coat
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Why are viruses considerd nonliving?
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they do not carry out respiration
they dont grow they dont move all they do is reproduce (with help of a host cell) |
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Viral Structure
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inner core of nucleic acid (DNA or RNA)
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Capsid
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outer protein coat
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Viral genomes
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May consist of
Double or single stranded DNA or Double or single stranded RNA depending on its its type of nucleic acid, a virus is called a DNA virus or an RNA virus |
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Viral Capids
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a protein shell that encloses the viral genome
capsids are built from protein subunits called capsomers capsid can have various structures |
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Viral envelopes
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surround the capsids of influenza viruses and many other viruses found in animals
membranous envelope help them infect host |
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How do Viruses Harm cells
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Viruses may damage or kill cells by causing the release of hydrolytic enzymes from lysosomes |
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Viral replication |
Occurs only in host cells Each virus has a limited number of cells that it can infect (host range) Described in terms of bacteriophages 2 mechanism: lytic and lysogenic
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Viral replication 2 |
-Before a virus can replicate, it must enter a host cell. .NOT all viruses can attack any cell .Virus must recognize the receptor site on the plasma membrane of host cell -Once attached, the virus must get inside and take over the host cell -The virus destroys the host's DNA .reprograms the DNA to make new viruses
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Lytic Cycle |
Replicates Viruses and kills the host cell produces new phages and lyses (break down) the host's cell wall, releasing the viruses
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Steps in the Lytic Cycle |
-Attachment of phage (using tail fibers) -Phage DNA inserted into bacteria; bacterial DNA is broken down -Viral DNA and proteins are made -New Bacteria are put together -Bacterial/ host cell is lysed and new viruses are released |
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Lysogenic Cycle |
-Replicates the phage genome without destroying the host -Viral DNA is incorporated into the host cell's chromosome -This integrated viral DNA is known as prophage -Host cell divides then copies the phage DNA and passes the copies to daughter cell
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Steps in the Lysogenic Cycle |
-Attachment of Phage -Injecting DNA into bacteria -Phage DNA added to bacterial DNA -Bacterial cell divides passing on prophage |
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Lystic vs. Lysogenic |
An environmental signal can trigger the virus genome to exit the bacterial chromosome and switch to the lytic mode. -Phages that use both the lytic and lysogenic cycles are called temperate phages
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2 Variables used to classify viruses that affects animals |
-DNA or RNA? -Single-stranded or double stranded? |
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Viral Envelopes |
Viral glycoproteins on the envelope bind to specific receptor molecules on the surface of a host cell. |
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Viruses using RNA |
-RNA genomes is found in viruses that affect animals. -Retrovirus use reverse transcriptase to copy their RNA genomes into DNA -HIV is a retrovirus that causes AIDS
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Viroid and Prions |
-Less complex disease causing agent -Viroids- infect plants and disrupt their growth -Prions- are slow-acting, virtually indestructible infectious proteins that causes brain disease in mammals -Things caused by Prions .Mad Cow disease .Scrapie, in sheep |
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Treatment and Prevention of Viruses |
-Viral infections cannot be treated by antibiotics -Antiviral drugs can help to treat, though NOT cure viral infections |
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Vaccines |
-Harmless versions of viruses that stimulate the immune system to mount defenses against the harmful pathogen -Vaccines can prevent certain viral illnesses
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Emerging Viruses |
-Those that suddenly become apparent -Flu epidemic are caused by new strains of influenza virus to which people have little immunity. -New viral diseases can emerge when viruses spread from animal to human
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Epidemic vs. Pandemics |
Epidemic, exp: H1N1, spread from Mexico to USA Pandemic, exp: Swine Flu, spread from animal to human |
