Viruses Flashcards
Adenovirus causes
Epidemic keratoconjuctivitis
Rhinitis
Capsid
Shell that encloses genome
Envelopes
Lipid containing membrane that surrounds some virus particles
Acquired when viral nucleocapsid buds thru cellular membrane during maturation
Budding happens where virus proteins have inserted into host cell membrane
Virus are
Obligate intracellular parasites
DNA OR RNA
NO ENERGY
RNA virus 3 types
Can be:
Single stranded (+sense or segmented -antisense)
Double stranded segmented
Reverse transcribing
Influenza/ SARS
+ sense RNA
Has genome of messenger sense RNA form
+ strand acts as a messenger RNA
Gets translated by hosts ribosome immediately
MAKES PROTEINS
ie. hepC
- strand antisense RNA
Must be transcribed with viral RNA dependent RNA polymerase to make + strand which is then translated
Polymerase is found in the capsid
Virus carries its own
DNA virus types
SS DNA mostly found in environment
DS DNA ie herpes
Positive strand used as template to make mRNA –> protein
Retrovirus
RNA –> DNA via reverse transcriptase
Ie hiv
Icosahedral
Capsid structure:
Capsimeres arranged into equilateral triangles
DNA or RNA is in the capsules
Helical capsid
Capsomeres are bound to RNA
Coiled into helical nucleoprotein capsid
Spherical shape mostly
Rabies = bullet shape
Viral glycoproteins
Are on envelope Attach virus to target cells Involved in membrane fusion step of infection ANTIGENS involved w/ neutralizing antibody
DNA viruses
HHAPPPy
Herpes Hepadinovirus Adenovirus Papova virus Parvo virus Pox virus
Properties of DNA viruses
Persistent infection
Transcription is temporally regulated
Genome stays in nucleus
Interact with host transcriptional machinery
Characteristics of RNA viruses
Transient
Mostly SS
Mostly enveloped
Mostly helical capsid
Replicate in cytoplasm (except retrovirus n orthomyxovirus)
Exceptions: picornavirus (foot n mouth disease)
Calcivirus (diarrhea)
Reoviridae (diarrhea)
Viral replication stages
AUSR
Attachment - followed by adsorption (susceptible to neutralizing antibody) and penetration (insensitive to neutralizing antibody)
Uncoating - release of nucleic acid from capsid
Synthesis and Assembly of viral products - also inhibits host cell mechanisms
Release of progeny from host cell
Polyprotein
Host cell ribosomes translate this
Fusion of many viral proteins
Protease cleaves polyprotein
Allows for release is rna polymerase
DNA virus replication
- Converted to early mRNA
Carries info for enzymes needed for DNA replication - Viral DNA replication - late mRNA transcribed from progeny DNA
2 types of virion release
Naked or enveloped
Transformation
Oncogenes may be introduced and may be uncontrolled and uninhibited cell growth cancer
Persistent infx
Ability of evading immune response
Able to attenuate virulence
Adenovirus E3/19K n CMV-US11 block cell surface expression of MHC1 proteins
Thus diminished presentation of viral antigens to cytotoxic T lymphocytes
Pox virus able to encode immunomodulatoeh molecules ie. CrmA - blocks T cell mediated apoptosis is virus infected cells
Plasmacytoid dendritic cell
Innate immune response
Recognizes virus and creates soluble proteins - interferons which impede viral replication
Type 1 ifn
Principal cytokines in antiviral response
Made by uncleared cells in response to virus
Interferons
First active defence against viral infection
Alpha n beta - type 1
Gamma - type 2
Activate antiviral defence in target cells to block replication
Enhance T cell recognition of infected cell
Neutralizing antibody
Impt for vaccine mediated protection
Neutralize free virus particles
Do activities against infected cells
HIV is able to avoid neutralizing antibodies
