Lec 13: Virology Flashcards
Effect of viral infection on animal cells
Cell death - cytocidal infection
Infection does not always result
Cytopathic: microscopic/macroscopic degenerative changes/abnormalities in host cells infected with virus
Infection in eukaryotic cells
Cytocidal infection -> cell death through lysis
Persistent infections: may last years. Can reactivate
Cytopathic effects: degenerative changes, abnormalities
Transformation to malignant cell
Tumour
Growth or lump of tissue
Benign: remain in place go form compact mass
Malignant: spread through body (metastasis)
Neoplasia
Abnormal new cell growth & reproduction (loss of regulation)
Anaplasia
Reversion to more primitive or less differentiated state
Oncovirus
Can cause cancer
Carcinogenesis
Complex, multistep process
Mutations in multiple genes
Involve oncogenes
How viruses cause cancer
Viruses can alter normal regulation of cell growth/differentiation (mutating genes directly or changing their expression)
Proto-oncogenes allow cell division. Expressed if cell receives appropriate signal
Tumour suppressor gene provide checkpoint to cell growth
Other possible mechanisms as to how viruses can cause cancer
Viral proteins bind host cell tumour suppressor proteins -> no longer a growth checkpoint
Virus carry oncogene into host cell & insert into host genome -> stimulated activity of cellular proto-oncogenes -> alters cell regulation
Insertion of strong viral genetic elements next to cellular oncogene -> overexpression
Cultivation of viruses
Requires inoculation of appropriate living host
Cultivated in broth or agar cultures of young, actively growing bacteria
Broth cultures lose turbidity (cloudiness) as viruses reproduce
Plaques observed in agar
Growing viruses in lab
Animal viruses can grow:
in living animals
embryonated eggs
in cell culture (cells from specific organs or animals)
Cell culture- propagation of viruses
Tissue treated with enzymes -> separate cells-> cells suspended in culture medium -> normal/primary cells grow in monolayer across glass/plastic container
Transformed cells or continuous cell cultures don’t grow in monolayer
Hosts for plant viruses
Plant tissue cultures
Plant protoplast cultures
Suitable whole plants (may cause localised necrotic lesions or symptoms of infection)
Quantification of virus
Direct counting of viral particles
Indirect counting: observable effect of virus. Haemagglutination assay and plaque assays
Viroids
Infectious agents composed of closed, circular ssRNAs
Replication requires host cell DNA-dependent RNA polymerase
Used as template for synthesis of new viroid RNA
Can produce latent infection or cause severe disease (RNA silencing- protects eukaryote from infection with RNA viruses)
