Viruses

• What do viruses have?

  Protein and nucleic acids
• What do viroids have?

  Only RNA
• What do Virusoids have?

  Only RNA
• What do prions have?

  Only proteins
• What are the characteristics of viruses?

  -non-cellular pathogens must infect host cells to reproduce

  -obligate intracellular parasite

  -single nucleic acid (RNA & DNA) contained within a protective protein capsid

  -composed of protein subunits called capsomers

  -spikes are glycoproteins that allow the viruses to attach and infect a cell

  Envelopes

  -plasma membrane taken from host

  enveloped x naked
• What is the host range?

  the spectrum of hosts a virus can infect

  -narrow x wide range

  -zoonoses: animals to humans

  -reverse zoonoses: humans to animals
• What is virus specificity?

  specific kinds of cells a virus can infect
• Describe viruses' morphology


  helical, cylindrical, complex, icosahedral, enveloped, filamentous
• What are the characteristics used to identify viruses?

  nucleic acids, mechanism of multiplication, morphology, and other chemical characteristics
• What are the possible genome organization in viruses?

  Double-stranded RNA (dsRNA)

  Positive-sense single-stranded RNA (+ssRNA)

  Negative-sense single-stranded RNA (-ssRNA)

  Circular genomes

  Segmented genomes

  Retroviruses

  Ambisense RNA viruses
• Lytic phase of virus replication


  A viral reproductive cycle in which copies of a virus are made within a host cell, which then bursts open, releasing new viruses
• Stages of the lytic phase

  1. Attachment: phage attaches to receptors

  2. Penetration: phage injects genetic material into the host

  3. Biosynthesis: viral genetic material takes over the host cell's machinery to replicate itself

  4. Maturation: newly synthesized viral components are assembled to for complete virions

  5. Release: Newly formed virions break open the host bacterial cell, releasing multiple copies of virus particles
• Lysogenic phase of virus replication



  The phase of virus replication that involves the integration of the viral genome into the host cell's genome, allowing the virus to persist within the host cell without causing immediate harm. The integrated viral DNA can remain dormant or be activated to enter the lytic cycle
• Stages of the lysogenic cycle

  1. Attachment and penetration: phage attaches to receptors and injects genetic material

  2. Integration: genetic material integrates into the host bacterial cell's chromosome. Becomes part of the host cell's genome and is replicated

  3. Replication and Cell division: As bacterial cell replicates its DNA and divides, the integrated DNA (prophage) is also replicated and passed on to daughter cells

  4. Induction: The process when certain conditions cause the prophage to enter the lytic cycle leading to the production of new viral particles

  5. Lytic cycle: leads to destruction of the host bacterial cell and the release of viral particles
• Temperate def:


  replicate via lysogenic cycle and change phenotype of host
• Virulent def:


  viruses replicate via lytic cycle
• Prophage def:


  genetic material of bacteriophage
• Lysogen def:


  harbors a prophage in the genome
• Conversion def:

  bacterium acquires new phenotype or change in characteristics
• Induction def:


  when a prophage is activated to enter the lytic cycle from lysogenic cycle
• Latent infection:


  time between infection and onset of viral replication
• Chronic infection:


  long-lasting condition
• Strategies viruses use to replicate inside host cell:

  Viral rep. entry and uncoating

  -entire genome or nucleocapsid

  -varies between naked and enveloped virus

  -Three methods:

  1. Fusion

  2. Endocytosis

  3. injection of nucleic acid
• How can viruses produce DNA using RNA as a template?

  -Entry into host

  -Reverse transcription

  -Synthesis of second DNA strand

  -Integration into host genome

  -Transcription and translation

  -Assembly and release
• How do viruses acquire an envelope?

  Through budding
• What are the possible outcomes of a viral infection?

  Cytocidal infection: kills host cell

  Cytopathic effects: degenerative changes, abnormalities transformation to malignant cells
• Explain how viruses are linked to cancers?

  -viruses that invade cells and form provirus that can lead to physical and genetic change

  -leads to uncontrollable division of the infected cells by controlling masses

  -chronic state of inflammation
• What are the phases and characteristics of the viral growth curve?

  1.Inoculation: inoculum of virus binds to cell

  2. Eclipse: virions penetrate the cell

  3. Burst: host cells release many viral particles

  4. Burst size: number of virions release per bacterium
• How are viruses cultivated?

  -living animals

  -in embryonated eggs

  -cell cultures

  -bacteriophages grown in bacteria
• How are viruses isolated?

  centrifuge or filtration
• What assays can be used to detect and identify viruses?

  -Cytopathic effects

  -Serological tests (western blotting of the virus w/ antibodies)

  -Nucleic acids (RFLPs and PCR)

  -Hemagglutination assay

  -Enzyme immunoassay
• What are viroids?

  infectious agents composed only of closed circular ssRNAs

  -smallest known infectious agents

  -don't code proteins

  -cause disease in plants
• What are virusoids?


  -Similar in structure to viroids

  -Covalently closed, circular infectious, but they encode for one or more gene products

  -need a helper virus to infect a cell
• Prions, diseases they cause, type of damage to cells


  -join together to form rods that accumulate in the brain causing tissue damage, cell death, and loss of neurons

  -inherited and transmissible by ingestion, transplant, and surgical instruments

  Diseases caused:

  -scrapie in sheep

  -BSE: mad cow disease

  -CJD

  -Kuru