Viruses Flashcards
Define virion
A single infectious virus particle comprised of a capsid, a genome, and sometimes an envelope
Define capsid
A capsid is composed of capsomeres and is a protein coat that provides shape and protection
Define envelope
A lipoprotein layer derived from the host cell membrane that surrounds the capsid
Define CPE
The cytopathic effect is the visible structural changes in a host cell’s morphology when it’s infected by a virus.
Define TSE
Transmissible spongiform encephalopathies are prion diseases which are fatal and neurodegenerative (e.g. scrapie, mad cow disease, chronic wasting disease, kuru, and Creutzfeldt-Jakob disease).
Explain why viruses are classified as nonliving microbes
They are acellular and depend on a host for survival (obligate intracellular pathogens). They have inert nucleus acids that do not activate unless they are inside a host (cannot reproduce on their own)
Describe features and functions of spikes
Spikes are viral proteins that extend from the capsid and through the envelope. They provide host cell specificity (help with host cell attachment/entry).
Described the generalized steps for bacteriophage replication
- Attachment: the virion attaches to the host cell
- Penetration: the viral DNA enters the host cell (the viroid’s protein coat remains outside)
- Synthesis of viral nucleic acids and protein
- Assembly and packaging of new viruses
- Cell lysis and release of new virions
Describe the steps for animal virus replication
- Attachment: viral surface proteins interact with host plasma membrane proteins
- Penetration occurs by fusion or endocytosis
- Uncoating: genome is released from capsid
- Replication: genome is replicated and viral proteins are made
- Assembly: new virions are assembled
- Release: virions are released by budding or lysis
Compare and contrast structure and replication of enveloped and naked animal viruses
Enveloped viruses have an envelope and can enter a host cell through membrane fusion OR receptor-mediated endocytosis (naked viruses can only do the second one)
Describe the 4 possible outcomes of animal virus infection
Virulent infection: lysis of host cell (most common)
Latent infection: viral genome exists in the host genome as a provirus and virions are not produced; host cell is unharmed until/unless virulent pathway is triggered.
Persistent infections: slow release of virions from host cell by budding does not result in cell lysis.
Transformation: conversion of normal cell into tumor cell
Distinguish between + stranded and - stranded RNA viruses
Positive-stranded RNA viruses serve as both the mRNA and genomic material, and is translated into proteins by the host cell’s ribosomes. Negative-stranded RNA is used as a template to produce positive-stranded viral genomes, which can then be translated, replicated, or packaged.
Identify 2 viral families that cause tumors
Polyoma virus S V40 and Herpesviruses
Describe lab methods for culturing and identifying viruses
Viruses cannot be seen with a light microscope, so plaque assays are used as well as observations of cytopathic effect. Immunologic methods (serology) and molecular methods (DNA sequencing or PCR or other stuff) are also used.
Describe viroids and prions as infectious agents
Viroids are infectious RNA molecules that lack a protein component (naked RNA with no protein capsid) and are the smallest known pathogens.
Prions are infectious proteins whose extracellular form contains only protein, no nucleic acid. They are known to cause disease in animals (no plant prion diseases discovered yet). The disease itself is caused when normal proteins in the body become abnormal and clump in the brain, which leads to brain damage and death.
