Microbio Ch. 13: Viruses, Viroids, Prions

Distinctive features of viruses

Obligatory intracellular microbes with DNA or RNA, lacking ribosomes and ATP-generating mechanisms.

Difference between viruses and bacteria

Viruses lack cellular structure, independent metabolism, ribosomes, and ATP-generating mechanisms.

Host range definition

The spectrum of host cells a virus can infect, determined by specific attachment sites.

Definition of a virion

A complete, fully developed viral particle.

Viral capsid structure

A protein coat made of subunits called capsomeres.

Origin of the viral envelope

Derived from the host cell's plasma membrane during viral budding.

Function of viral spikes

Carbohydrate and protein projections on enveloped viruses used for attachment.

Main morphological types of viruses

Helical, polyhedral, enveloped vs. naked, and complex structures.

Helical viruses

hollow, cylindrical capsid

Polyhedral viruses

many-sided

Viral taxonomy naming rules

Genus names end in -virus; family names end in -viridae.

Growing bacteriophages in the lab

bacteriophages form clearings called plaques on agar.

Methods for growing animal viruses

In living animals, embryonated eggs, and cell or tissue cultures.

virus injected into eggs result

grow viruses for vaccines

primary cell line

derived directly from animal tissue slices

continuous cell lines

derived from cancerous or transformed cells (e.g. HeLa cells)

Cytopathic effects (CPE)

Visible destructive changes or deterioration of host cells caused by viruses.

Examples of cytopathic effects

Cell lysis, syncytia formation, inclusion bodies, and cell rounding or detachment.

syncytia formation

fusion of adjacent cells into multi-nucleated giant cells

inclusion bodies

dense clusters of viral proteins or nucleic acids visible within the cytoplasm or nucleus

Serological tests for viruses

Enzyme-linked immunosorbent assays (ELISA) and Western blotting.

western blotting

technique that uses antibodies to detect the presence of specific proteins separated by electrophoresis

Eclipse period

Period of time where the host cell does not appear to be infected.

Bacteriophage multiplication cycles

The lytic cycle and the lysogenic cycle.

Stages of the lytic cycle

Attachment, penetration (through phage lysozome), biosynthesis (normal host cell functioning halts), maturation, and release.

What is a prophage?

Phage DNA that is incorporated into the host cell's DNA.

What is the first step of animal virus multiplication?

Attachment

What is the second step of animal virus multiplication?

Penetration (through receptor-mediated endocytosis or fusion for enveloped virus)

What is the third step of animal virus multiplication?

Uncoating

What is the fourth step of animal virus multiplication?

Biosynthesis

What is the fifth step of animal virus multiplication?

Maturation

What is the final step of animal virus multiplication?

Release (through budding for enveloped viruses, ruptured for nonenveloped viruses)

Replication site of animal DNA viruses

In the nucleus of the host using DNA polymerase.

Key enzyme for RNA virus replication

RNA-dependent RNA polymerase (RdRp).

Mutation rate of RNA vs DNA viruses

RNA viruses have a high mutation rate; DNA viruses have low rates.

Why do viruses use RdRP

Human cells don't have an enzyme that copies RNA directly from an RNA template

+ssRNA

act directly as mRNA

-ssRNA

cannot be read, need to carry RdRp

Multiplication of retroviruses

They use reverse transcriptase to produce DNA that integrates as a provirus.

Examples of retroviruses

Human Immunodeficiency Virus (HIV) and Human T-cell Lymphotropic Virus (HTLV).

Teratogenic virus definition

A virus that crosses the placenta and causes embryo or fetus malformations.

Examples of teratogenic viruses

Zika virus, Rubella virus, Cytomegalovirus (CMV), and Herpes Simplex Virus (HSV).

Mechanism of oncogenic viruses

They integrate into host DNA, activate oncogenes, or disrupt tumor suppressor genes.

Examples of DNA oncogenic viruses

Epstein-Barr virus (EBV), Human papillomavirus (HPV), and Hepatitis B/C viruses.

Acute vs. persistent viral infections

Acute infections have rapid onset and clearance; persistent involve long-term continuous presence.

Three main types of persistent infections

Chronic, latent, and slow infections.

Example of a latent viral infection

Herpesviruses, such as Varicella-Zoster Virus and Herpes Simplex Virus.

Epstein-barr virus

Burkitt's lymphoma, nasopharyngeal carcinoma

Human papillomavirus

cervical and anal cancer, oropharyngeal cancer

hepatitis B and C virus

liver cancer

RNA oncogenic viruses and cause

human T-lymphotropic (HTLV-1 and HTVL-2), adult T cell leukemia and lymphoma

Example of chronic disease

Hepatitis B and C (HBV and HCV)

Definition of a prion

Proteinaceous infectious particles inherited by ingestion, transplant or surgical instruments

Prions characterization

sponge-like lesions/ spongiform encephalopathies

Examples of prion diseases

Mad cow disease, Creutzfeldt-Jakob disease, and sheep scrapie.

Mechanism of prion disease

Conversion of normal host protein PrPC into the infectious misfolded form PrPSc

What are PrPsc

scrapie protein; accumulates in brain cells causing cell death and forming plaques in brain tissue