1:Structure/Classification/Pathogenesis Flashcards
(38 cards)
Four characteristics of Viruses:
- Nucleic acid genome packaged in a protein coat. Protein for protection and genome for initiation and completion of infectious cycle.
- Unable to generate energy or synthesise proteins. Must make mRNA that can be translated by host ribosomes.
- Replication, not growth or division.
- Enter hosts via cellular receptors.
Where do viruses function?
They are obligate intracellular parasites, meaning their genome can only function within a living cell.
Functions of the nucleocapsid?
Protecting the viral genome, transmission and infection.
Characteristics of icosahedral nucleocapsids:
Package DNA or RNA, released by lysis (non-enveloped), or by budding (enveloped viruses).
Characteristics of helical nucleocapsids:.
Protein subunits wrapped around genome, usually packaging RNA, usually enveloped and associated with matrix protein.
Immunogenic components of viruses?
The envelope, if present, or the nucleocapsid. They are immunogenic because they contain antigenic epitopes.
Method of envelope budding
Expression of viral proteins cell membrane, nucleocapsid buds through membrane, forming the envelope.
Pros/Cons of an envelope
Pros: Surrounds the nucleocapsid, aids in transmission and infection.
Cons: Confers instability, may be easily dehydrated.
3 Methods envelopes develop:
- Budding from the plasma membrane
- Bud into cytoplasmic vesicles, released by exocytosis.
- Budding through the nuclear membrane.
Location of viral matrix protein
Located between the the envelope and the nucleocapsid in viruses that bud from the plasma membrane.
Location of tegument protein
Between NC and envelope in viruses that bud from the nuclear membrane.
Characteristics of Virus genomes
RNA or DNA
Single or Double stranded
Segmented, linear or circular.
Contains open reading frames.
Functions of viral genome
Acts as mRNA or template for mRNA.
Template to produce new progeny genomes.
Viral enzymes are…
…contained within the NC, composed of protein and present in the virion only if they are needed prior to mRNA production.
Functions of viral enzymes in the NC
Polymerase: Makes new genomes or mRNA
Integrase: Integrates HIV DNA into chromosome.
Protease: Digests virus polyproteins.
Picornaviridae
+ve ss RNA, icosahedral naked NC, cytophatic (NC released by lysis).
e.g. Poliovirus
Hepadnaviridae
ds DNA, icosahedral NC, enveloped.
e.g. Hepatitis B virus
Flaviviridae
+ve ssRNA, icosahedral NC, enveloped, released by budding in ER->Exocytosis.
e.g. Hepatitis C virus
Retroviridae
+ve ssRNA, 2 gene copies, icosahedral NC, Matrix, enveloped.
e.g. HIV
Orthomyxoviridae
- ve ssRNA, segmented genome, helical NC, Matrix, enveloped, released by budding from plasma membrane.
e. g. Influenza A virus
Herpesviridae
ds DNA genome, icosahedral NC, tegument proteins, enveloped, buds through nucleus.
e.g. Herpes simplex virus, varicella Zoster Virus.
Stage 1 of viral pathogenesis:
- Attachment
- Penetration
- Uncoating
Stage 2 of viral pathogenesis
- Gene expression
5. Gene replication
Stage 3 of viral pathogenesis
- Assembly of nucleocapsid
- Packaging of genome and proteins
- Release from cell
