viruses

general properties of viruses

-Poison or venom

Composed of protein, nucleic acid and occasionally lipids
- no ribosomes and only ONE type of nucleic acid

Genome

- DNA or RNA, never both
- genome can be circular or linear
- genome can be "segmented"-

Viruses require

a host cell for replication
- no metabolic pathways

Obligate Intracellular Parasites

- require a host cell for replication

virion

-complete, fully developed viral particle
- nucleocapsid (genome + capsid (protein "shell"))

capsid

Outer protein coat of a virus

Icosahedral

Papovaviridae (Papillomavirus)

HPV
Warts

Herpesviridae- Varicella-zoster (VZV)- Epstein-Barr (EBV)

VZV= chicken pox
EBV= mono

helical

Complex

-don't fit into other categories
-multi-component
- more genes involved in the structure

Virus lifecycle

1)attachment, 2)penetration, 3)early expression of nucleic acid
4) replication pf nucleic acid
5)synthesis
6)packaing and assembly
7)egress

attachment

virus attaches to specific host receptor

Penetration

- viral or "host" mediated
- nucleic acids to cytoplasm or nucleus
- entry in some cases of entire nucleocapsid

Early" expression of virus genes

depending on genome type
- could require specialized viral enzymes

Replication of virus nucleic acid

- could require specialized viral enzymes
- virus taking over cells and replicating nuc. acids

Synthesis of new virion components

structural proteins last to be synthesized

Packaging and assembly of new virions (Maturation)

"self-assembly"

Egress (exit from cell

lysis or budding

Viropexis

fusion penetration

virology

study of viruses

viruses are

acellular and non-living

Plaque

viral growth & replication
- cell lysis- inhibition of cell growth
- millions of virons at site
- PFU = plaque forming units