CHAPTER 13 characterizing viruses and prions

Viruses

• Acellular

• cannot carry out any metabolic pathway

• don’t grow or respond to environment

• must have host to reproduce

• no cytoplasmic membrane, cytosol, or organelles

• DOES have DNA or RNA

Genetic material of viruses

• may be DNA or RNA but never both

• may be linear or circular

• much smaller than genomes of cells

• composed of A,T,C,G,U

• double strand or single strand

Extracellular state

• Not yet in host

• has protein coat called CAPSID

• some have phospholipid envelope

Intracellular state

• Capsid removed

• viruses exists as nucleic acid

• inside host

function of capsid

protection and attachment

capsomeres

protein subunits that make up capsids

Helical

is the shape of a spring

polyhedral

is a hexagon type shape

complex shape

anything other than helical and polyhedral

viral envelope

• acquired from host cell

• composed of phospholipid bilayer

• some proteins are virally coded glycoproteins

• more fragile

viral specificity

• viruses infect only specific species

• some may only affect specific cell in host

Direct penetration

• injects DNA

• naked virus entry

Fusion

• cell membranes blend together

• enveloped entry

Endocytosis

• cell absorbs virus

• naked and enveloped entry

Lytic replication

1. Attachment

2. Entry of new nucleic acids (injects)

3. synthesis of new nucleic acids (reproduce)

4. Assembly (make capsid)

5. Release

Lysogenic Replication

• Modified replication cycle

• infected host cell grow and reproduce normally before they lyse (release)

• same steps but there is delay

• EX: herpes

Latent or proviruses

• when animal viruses remain dormant in host cells

• may be prolonged for years with no viral activity

• host DNA is permanent

Antiviral medications

• Virus specific

• inhibit replication

• often difficult to not harm the host cell

• rely on immune system to eliminate

• given within first 24 hours of signs

Cellular PrP (prion proteins)

• made by all mammals

• Normal, functional and had alpha helices

Prion PrP (prion proteins)

• Disease-causing form has beta pleated sheets

• not normal

• leads to neurologic damage

The prion doesn’t produce like other infectious agents but instead…

converts the normal cellular PrP to become Prion PrP

Spongiform encephalopathies

• holes in brain or spinal cord

• CWD, kuru, and vCJD

• transmitted by ingestion and mutation

• No standard treatment

Getting rid of prions

• normal sterilization do not deactivate prions

• can only be destroyed by incineration