Viruses 1 Flashcards
Virus discovery
Chamberland filters removed bacteria from extracts
- yet extracts still caused disease
.:. microbe distinct from + smaller than bacteria caused disease
Virus nature + structure defined by electron microscope
What are viruses?
Non-cellular parasitic microbes
- w/ no intrinsic metabolic capabilities
Obligate intracellular parasites
- can only replicate inside living host cells
Viral replication
- Virus attaches host cell
- Capsid penetrates cell
- Uncoating of capsid
= DNA released - Viral DNA + proteins synthesised via host machinery
- Assembly of new virions
- Release + maturation of virions
General characteristics of viruses
Simple structures
- few/no enzymes of their own
- consist of NAs + protein
Size
- smaller than almost all microbes
- 20nm-400nm
- size of virus unrelated to size of target host cell
Virus structure
Capsid encloses genome
- symmetrical
Some have an outer lipid envelope
capsid function
protect viral genome
facilitate entry into cell
genome
- size
- made of
small compared to other orgs
DNA or RNA
(most bacteriophage =DNA
all plant + most animal = RNA)
capsomeres
subunit of capsid
capsid mad euphorias of many individual capsomeres
nucleocapsid/core
capsid w/ enclosed NAs
tegument
space between nucleocapsid + envelope
may contain accessory viral proteins
virion
complete mature virus particle
metabolically inert
envelope
lipid membrane surrounding complex viruses
may contain glycoproteins
derived from host cell membrane during budding of viruses
capsid
- why are capsomeres a fundamental property?
economy of genetic info
ease of capsid assembly
ease of intracellular release of viral genome
economy of genetic info
allows virus to generate capsids from min level of genetic info
ease of capsid assembly
virus particles can self-assemble
+ held together by intra-molecular forces NOT covalent bonds
.:. no additional enzyme needed to join subunit s