Virus Flashcards
Why is it not possible to grow virus in artificial media?
bc viruses are obligate intracellular parasites - requires a host (cell) to replicate in
List the main structures of an enveloped virus.
- capsid (protein coat) made up of capsomeres (w/ nucleic acid inside)
- envelop (membrane)
- protein projections (for attachment on host cell)
What are the main functions of structural proteins?
make up the viral structure
> facilitate entry into host cell (protein projections)
> protect viral nucleic acid (capsid)
> stabilisation: keep structure tog.
What are the main types of viral capsid symmetries & e.g? (3)
- Icosahedral (cubic) e.g. herpesvirus
- Helical: spiral e.g. coronavirus
- Complex: neither icosahedral or helical e.g. bacteriophage T4
What is the main classification difference b/w parvovirus & picornavirus?
- Parvovirus: Nucleic acid is DNA
- Picornavirus: RNA
List the Baltimore classes of virus
Class:
1: dsDNA
2. ssDNA
3. dsRNA (segmented)
4. ssRNA +sense (already an mRNA)
5. ssRNA -ve sense (needs to be converted to +ve)
6. ssRNA +ve sense w/ dsDNA intermediate (before replication). MEANS: RNA + reverse transcriptase => DNA => mRNA
7. dsDNA w/ +ve sense (ssDNA). undergo reverse transcriptase => mRNA
List the main replication events of a virus
- Attachment to specific host cell’s receptor on membrane
- Penetration: enter host cell & “uncoats” capsid
- Replication of viral genome: production of viral mRNA
& early viral proteins (non-structural> assist in replication) - Production of late viral (structural) proteins
- Assembly of the progeny virions
- Release of virions
What’s the diff. b/w lytic & lysogenic cycles?
- Lytic: lysis of host cell to release viral particles
- Lysogenic: viral genome integrated in host chromosome (- prophage). May enter lytic cycle
Describe the 2 mechanisms viruses cause disease
- Replication w/in host cell => damage in cell
2. Damage form host defenses in its attempt to remove virus from infected cells
Describe the host factors that are important in viral infections
- Appropriate receptors on surface: determine if virus gets entry
- Internal cellular environment suitability: molecular machinery for replication (@ S phase) is present, & physical environment is suitable
What is “CPE” and how does it occur?
Cytopathic effect: is the effect of viral replication on host cell. It occurs since host cell’s function will change = detectable
What is the main action of HIV as a result of AIDS?
T helper cells have CD4 receptor - HIV binds to => destroys T helper cells => destroy humoral/adaptive immune resp.
List the events of a viral infection
- Invade host
- Replicate in cells of inoculation
- Overcome local defences
- Spread to other cells & other areas
- Replicate again
- Exit from host in lrg no. to infect another host
How can viruses evade the immune system? (7)
- poorly immunogenic (stimulate IR)
- Not displaying enough of their antigen on the surface
- Inactivate B cells, T cells, macrophages
- Interfere w/ expression/transport of MHC proteins
- excess antigen production > neutralise antibodies
- mutations - change antigens of virus
- infection to foetus before immune system has developed
What is the incubation time for measles?
13-14 days
What does “recruitment” mean in relation to prion disease?
When a normal protein gets in contact w/ an abnormal protein => that normal protein will be converted into an abnormal conformation
*Describe the types of clinical manifestations (signs & symptoms) resulting from viral infections.
*skin rashes, low immunity, transformation of cells, inclusion bodies, syncytia, lysis
Describe the basic structure of a Herpes virus.
- Linear dsDNA
- Nucleocapsid
- Tegument (proteins)
- Lipid envelop
- envelop proteins
What does VP16 do in Herpes virus infections?
VP16 protein (in tegument) activates a genes(/phase) but requires host’s proteins Oct 1 & HCF (human factor C)
Once Herpes virus is in the cell, describe phases of gene expression
- 1 phase activates the next & inhibits the previous
1. a-phase: a gene (regulator) activated by VP16 protein
2. B-phase: B gene -> (early) proteins for DNA replication
3. Y-phase: gamma gene -> (late) structural proteins
*What are the differences between “chicken pox” and “shingles”?
*“chicken pox” is an acute infection while “shingles” is a latent infection
What are the functions of the Haemagglutinin (H) and Neuraminidase (N) surface protein spikes on the influenza virus?
- Haemagglutinin: binds to sialic acid on mucous memb. & RBC, & causes ENTRY in host cell
- Neuraminidase: release virions (EXIT out of cell)
What’s the genome of influenza virus & Where in the host cell does the genome replicate?
- (Class 5) ss(-) RNA segmented genome
- repicate in nucleus
What are “Antigenic Drift” and “Antigenic Shift”?
- Drift: minor changes in H & N bc host selection of mutants (mutations freq. in RNA bc no proofreading)
- Shift: major change in H & N from recombination b/w animal & humans bc Hi chance of reassortment of segmented RNA (e.g. when 2 diff. virus infect the same cell genes can be interchanged = new cell)
Entry of a virus in mucous memebranes is easy/difficult?
Esay bc epithelial cells (line mucosal lining) are thin: can pass through/ absorbed w/ ease
How do DNA viruses replicate?
General idea in class 1 (& 2): (ssDNA->) *dsDNA -> mRNA Class 7: make full dsDNA (from partial dsDNA & ssDNA) -> mRNA -> rvs transcriptase = partial DNA to package
How do RNA viruses replicate?
- need to end up w/ +ve sense aka mRNA
Class 3: -ve sense in ds RNA -> +ve (mRNA)
C5: -ve ssRNA -> +ve (mRNA)
C6: ssRNA -> rvs transcriptase = dsDNA -> lysogenic -> transcribe to mRNA
