Viruses Flashcards
What is a virus?
What are the key properties of a virus?
What does virus need to replicate?
Small infectious obligate intracellular parasite
Viruses= chemicals
Not living
Cannot reproduce on own i.e require mechinery + energy + substances from other cells
Self-form into structures i.e. icosahedreal or helical
Ribosomes
Polymerases
Trascriptase enzymes
What is the basic structure of a virus?
DNA or RNA contained in capside protein + nucleocapsid= forms naked capsid virus
Enveloped in glycoprotein + lipid membrane
What is the current viral classification system based on?
Type + structure of viral nucleic acid and strategy of replication
Type of symmetry of viral capsid i.e. helical or icosahedral
Presence or absence of lipid envelope
What are the stages of the infection cycle of a virus?
What is viral tropism
ATTACHMENT
-virus detects cells which have surface receptors it can recognise e.g. CD4 glycoproteins for HIV
PENETRATION
DISASSEMBLY
-virus exposes viral genome
TRANSCRIPTION
-Viral enzyme transcribe the viral genome to form viral mRNA
TRANSLATION
-mRNA translated to form viral proteins using the cell mechinary
GENOME REPLICATION
-viral enzymes enable replication of viral genome
ASSEMBLY
-virus able to self-assemble the viral genome and the viral proteins to form new viruses
RELEASE
Viral tropism:
-ability of a virus to productively infect a given cell
What are the 2 types of transcription that can occur in viruses.
What is the potential advantage of the method used in retroviruses?
Normal transcription
-ds DNA -> RNA+ which can then be translated to produce viral proteins by the cells machinery
Reverse transcription= occurs in retroviruses
- viral RNA+ converted to DNA using reverse transcriptase
- viral DNA then incorporated into host DNA so it will be transcribed with the host DNA
Incorporating the DNA into host DNA can protect it from irradication and enable the virus to remain latent and undetected
What are the 4 possible outcomes of virus infecting cell?
Transformation of normal cell to tumour cell
-due to genome being changed to the extent it becomes cancerous
Lytic infection
-cell dies and releases virus
Peristent infeciton
-slow release of virus with cell remaining alive
Latent infection
-usual occurs when viral DNA incorporated into genome or nucleus
-period w/o replication + virus evades detection by immune system
Eg HIV/Herpes
What is an example of a virus that can reactivate later in life?
What is the pattern associated with reactivation?
Herpesvirus Varicella-Zoster (chicken pox)
-virus moves to dorsal root ganglion where it remains latent
Immune system depression or stress can lead to reactivation of the virus
-leads to SHINGLES i.e. rash appears on mucutaneous dermatome of the associated spinal nerve dorsal root ganglion
(Characteristic rash pattern)
Which viruses are associated with cancer?
How can the risk of this happening be decreased?
Human papillomavirus= cervical cancer
Hep B + = HCC
EBV= Burkitts lymphoma + Hogkins lymphoma
Herpes virus= Kaposi’s sarcoma
VACCINATION
How does the immune system respond to viral infections?
1st time infection:
-Host infected cell displays viral antigens via MHC2
-CD8 cytotoxic TC recognises abnormal antigens and binds
-Releases granules to induce self-destruction
I.e. virus no longer able to replicate
Response to secondary infection (post vaccine or when infected with previous virus)
- Antibodes can recognise virus and opsonise virus to prevent virus from entering cells (neutralising Ab)
- Acts to tag virus for destruction by neutrophils
NOTE:
-TC involvement= reason why viral infection tends to be associated with lymphocytopenia rather than neutrophilia (associated with bacterial infection)
What methods can be used to detect viral infections?
Viral cultures (requires cells so not really done that often)
Electron microscopy
Serology
-can be used to detect viral antigen or antibody (IgG)
PCR
-looks for sequence of DNA i.e. use primers specific for viral DNA which will lead to increased replication of this DNA
Real-time PCR
-indicates how much DNA over time
I.e. speed of increase in DNA corrsponds to number
What are the different methods used in serology depending on what you are trying to identify?
ANTIGEN
- might be attached to host antibody
- need to add secondary antibody with indicator which will bind to viral antigen
ANTIBODY
-need to add anti-Ab to bind to antibody in sample
I.e. anti-IgG for IgG
What are the possible targets of antiviral treatments?
Virus entry
- receptor antagnonist
- fusion inhibitors
Inhibit reverse transcription (in retroviruses)
- NNRTI
- NRTI
Intergration
-INSTs
Transcription
Translation
Cleavage= protease inhibitor
Assembly= protease inhibitor
Budding + matruation= protease inhibitor
What is the possible clinical use of bacteriophages?
Could be used to treat bacterial infection which are resistant to antibiotics
