Microbiology - Viruses Flashcards
Basic structure of a virus - how does this differ from bacteria and fungi
Virion - completely assembled infective virus
- protein shell (capsid) surrounds viral genome and is made up of protein subunits (capsomeres)
Differentiate between enveloped and non-enveloped viruses (include examples)
ENVELOPE - surrounds capsid and is acquired by budding through cellular membranes of the host
- contains host phospholipids and proteins + viral proteins and glycoproteins
NON-ENVELOPED - more resistant to environmental desiccation, lipid solvents or detergents
Basic principles of viral replication (10 steps)
- Must be inside host to replicate
1. Attachment
2. Penetration
3. Uncoating
4. Transcription of early mRNA
5. Transcription of early proteins
6. Replication of viral DNA
7. Transcription of late mRNA
8. Transcription of late proteins
9. Assembly of virions
10. Release
DNA viruses
- DNA is not transient or labile.
- Replication resembles host DNA transcription and replication
- Replicate in the nucleus (except pox viruses).
RNA viruses
- RNA is labile and transient.
- Genome structure determines the mechanism of transcription and replication
- Replicate in the cytoplasm
- More prone to mutation
Describe the difference between antigenic shift and antigenic drift and its implications in the outbreak of disease
Antigenic shift = Acquisition of a gene from a completely new Haemagglutinin or Neuraminidase (envelope proteins) from another influenza virus, resulting in new HN type
- new strains of influenza causing major flu pandemics
Antigenic drift = gradual accumulation of point mutations leading to new stereotypes
- minor change can produce a major outbreak e.g. fowl plague in Pennsylvannia
Types of cell interactions - Lysis of cell
E.g. herpesvirus
• Particles burst out of host cell into Extracellular space
• Resulting in death of host cell
• Once released enters new cell to multiply
Types of cell interactions - Persistent infections - Productive
PRODUCTIVE e.g. rabies virus
- Cells infect productively and not killed by replication process
- Released by budding
- No inhibitory effect on cellular metabolism
- Antigenic changes in infected cells
- Insertion of glycoproteins in plasma membrane
- Long term cellular change
Types of cell interactions - Persistent infections - Latent
- Restricted expression of episomal or integrate virus genome
- Few, if any, changes in the latently infected cell
Types of cell interactions - Persistent infections - Non-productive but transforming
- May make changes that convert a normal cell into a malignant one
- RNA: integrating own genetic material into cellular genome
- DNA: transformation by abortive/restrictive infections
Effects of viral infections on cell morphology - Cytopathic
- Virion infected cells release progeny virions that spread through the cell culture supernatant fluid to infect other cells
Effects of viral infections on cell morphology - Inclusion bodies
- Changes in cells infected with certain viruses
- May form masses of viral nucleocapsids e.g. rabies virus; masses of proteins/nucleic acids
Effects of viral infections on cell morphology - Alteration of cell membranes
Changes in plasma membranes of the cell by insertion of viral glycoproteins in the membrane of the host during viral replication
Effects of viral infections on cell morphology - Formation of syncytia
- May lead to fusion btw neighbouring infected/uninfected cells
→ fused cells allow viral nucleocapsids andnucleic acids to spread while escaping hosts defences e.g. Herpesviruses
Effects of viral infections on cell morphology - Haemadsoprtion
- Acquire ability to absorb erythrocytes due to glycoproteins in plasma membrane