Microbiology: Viruses, Viroids, and Prions
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- Basic Properties of the Polio Virus
-
1. +ssRNA
2. Icosahedral
3. Nonenveloped
4. Infects nerve cells
5. RNA can read like mRNA - RNA plus strand
- Genome is read the same, not complementary
- Life Cycle
-
1. Penetration and Uncoating
a. attaches to nerve
cell, then cell engulfs
2. Genome Replication
a. +RNA makes -RNA
b. viral RNA-dependent,
RNA polymerase;
packaged proteing
3. Gene expression
4. Assembly and Release - Gene Expression
-
- makes proteins
1. translation
2. auto-proteolysis and proteolysis - What virus can be translated without a eukaryotic 5' cap (methylguanosine cap? How?
- The Polio Virus inactivates translation of host mRNAs by DESTROYING THE HOST PROTEIN THAT RECOGNIZES THE METHYLGUANOSINE CAP.
- Basic Properties of Flu Virus
-
1. -ssRNA
2. segmented genome (8 pieces)
3. enveloped
4. helical capsid
5. infects mucus membrane cells of the respiratory tract i.e., nose and lungs - What does the segmented genome of the flu virus do?
- virus can mix and match genomes, allowing virus jumping.
- Flu Virus Structure
-
1. viral envelope
2. hemagglutinin, binds to cells
3. neuraminidase
4. segmented genome, -RNA - What kind of genome does the flu virus have?
-
-ssRNA which means that it is read complementary to the mRNA
-segmented - Can the flu virus genome act as an mRNA strand?
- No it cannot because it is -RNA not +RNA which means the genome must first be transcribed in order to be translated
- What does Hemagglutinin do?
- mediates the fustion of the viral envelope to the host cell membrane
- What does Neuraminidase do?
- Breaks down the sialic acid (sticky), and assist in budding (the release of virus from cell)
- An Antigen Shift is?
- A change on the outer membrane proteins
- Major Changes in viral protiens are due to?
- mixing of segmented genomes between viruses which occurs when two different viruses infect the same host, intern producing new virus strains
- What is an Antigen?
- what the immune system recognizes
- HIV (AIDS Virus)
- Human immunodeficiency virus
- What does HIV attack?
- CD4+ or T-cells, which are part of the immune system. These are proteins out the outter surface of the cell.Tcells help other immune cells function
- How many CD4+ cells do healthy humans have?
- 800 CD4+/T-cells per cubic millimeter of blood.
- When is an HIV patient considered to have AIDS?
- When their CD4+ count falls below 200.
- HIV facts (7)
-
1. Usually acquired by sex
2. Almost always fatal
3. No cure
4. No Vaccine
5. in US 1/250 have it
6. in US 1/3000 are infected each year
7. 8-10 yrs pass between HIV infection and developement of AIDS - HIV Prevention (4)
-
1. Celibacy
2. Insistence on condoms
3. Clean needles
4. Post-exposure drug treatment within 24hrs
a. 4 wk treatment with
possible side effects of
headache, nausea, fatigue
and anemia - How does HIV replicate?
-
HIV is a retrovirus, which means its an RNA virus that replicates through a DNA intermediate.
The HIV RNA must first be transcribed into DNA via reverse transcriptase. It then encorporates itself into the host genome, and the host replicates the virus. - HIV structure
-
1. Envelope protein, immune system response
2. reverse transcriptase
3. integrase, encorporates into our DNA
4. Protease, cuts polyprotein
5. +ssRNA - Gentic Map for retrovirus. 6 parts
-
1. LTR= long terminal repeat
2. gag
3. pol
4. env
5. other genese (specific to virus)
6. LTR - GAG encodes for?
- internal structural protein like capsid protein.
- What does pol encode for?
- reverse transcriptase
- The envelope proteins are encoded by?
- env
- what are the HIV proteins (4)amd what are their functions?
-
1. Viral envelope protein:
mediates binding to CD4
receptor
2. Reverse Transcriptase:
synthesizes DNA from RNA
template
3. Integrase: splices viral
DNA into host genome
4. Protease: cleaves the
viral polprotein into
active parts - HIV reproductive cycle (7 steps)
-
1. penetration and uncoating
2. reverse transcription
3. integration
4. gene expression
5. replication
6. polyprotein cleavage by
HIV protease
7. assembly and budding - Once the virus is integrated into the host genome, what is it called?
- a provirus
- What are the 2 types of HIV treatment?
-
1. Reverse transcriptase
inhibitors
2. Protease inhibitors
Generally 2 reverse transcriptase inhibitors are used in combination with a protease inhibitor. - How does HIV develope drug resistance?
- via a mutation to the inhibitor binding site therefore allowing reactivation of protease function.
- What are Viroids?
- Virus like infections found in plants
- Properties of Viroids (3)
-
1. circular ssRNA
2. naked RNA, no protein
association
3. viroid genomes do not
encode proteins - What are prions?
- infectious proteins which appear to transmit disease without DNA or RNA
- What is the name of the prion diseases?
- spongiform encephalopathies, (makes brain look like a sponge)
- Types of Prion disease (3)
-
1. Scrapie in sheeps/goats
2. Mad Cow Disease
3. Creutzfeld-Jacob in
humans over 50 - Mad Cow Disease is also known as?
- Bovine spongiform encehphalopathy (BSE)
- what are the sources of BSE?
- Feeding cows with *meat and bone meal* remains of infected sheeps or cows, especially infected brain tissue
- Is a prion destroyed by cooking?
- Nope
- What is the New variant Creutzfeld-Jacob syndrome?
- Basically mad cow disease, in people under 30. most people die
- What is the incubation time for mad cow disease?
- 10 to 15 years
- How do prions cause disease?
- they're kind of like vampires, a normal protein comes in contanct with an infected protein. the diseased protein catalyzes a conformational change that turns the normal protein into a prion.
- The prion gene is
- a mutant form of a normal gene.
- Where are prions found?
- in normal genee found in animals.