6.2.1 Virus Stucture Flashcards
What are the properties of a virus?
Obligate intracellular parasite
Needs host cell to survive
Lacks organelles
Extremely small (filterable agents)
Need electron microscope to visualise
Describe the components of virus structure
Virus can be naked or enveloped
Viral envelope
Host derived lipid bilayer
Virus encoded glycoproteins
What is the difference between positive sense and negative sense in single stranded RNA viruses?
Positive sense - Can be translated directly to protein
Negative sense - Must synthesise positive sense strand before viral proteins can be translated
What is meant by a segmented viral genome?
Genome is divided into several parts
In RNA viruses each segments codes for one protein
How does replication of an RNA virus differ to a DNA one?
RNA required RNA polymerase to replicate, and is prone to error so more variable and can rapidly evolve.
What are the three capsid types?
Icosahedral
Helical
Complex
Describe icosahedral capsid symmetry
12 vertices
20 triangular sides (facets)
Composed of capsomers (structural unit)
5:3:2 symmetry
Describe helical capsid symmetry.
Structural unit is one capsid protein
Single capsid protein molecules arranged as helix
All helical viruses are enveloped
Describe complex capsid symmetry.
Usually large viruses >100 proteins
Neither helical or icosohedral structure
Characteristics of enveloped viruses
Irregular shape
Host-derived lipid bilayer
Contain receptors for virus entry
What are the methods of viral release from a cell?
Enveloped viruses - budding
Naked viruses - lysis
Function of virus capsid
Structure
Protection
Allows cell entry via receptors
Induces antibody response
Function of virus envelope proteins
Structure
Allows attachment and entry via receptors
