BIOL 2420 Exam4
Card Set Information
BIOL 2420 Exam4
5 Virus characteristics
1. Obligate intracellular parasites
2. Filterable, smaller than bacteria
3. Contain DNA or RNA as genetic material
4. Reproduce by assembly only inside another cell
5. Lack enzymes to produce ATP
•Protein coat or capsid
•Genome = Nucleic acids with or without associated polymerase enzymes
•With or without surrounding lipid membrane (Enveloped or naked)
Classification of virus
•Nucleic acid type
–DNA, RNA, ds versus ss (+ve or -ve sense), circular or linear, single chromosome or segmented
–E.g. Capsid structure, size, presence or absence of envelope
•Family, (genus), species
DNA Organizational Structure
RNA Organizational Structure
Steps for Virus Reproduction
3. Uncoating (only in animal viruses)
6. Release from cell
Cycle of Infection and Replication
How does Lysogenic cycle differ from lytic cycle?
1. Recombination of viral nucleic acids into the chromosome of the host acting like a transposon (prophage).
2. Production of repressors for the synthesis of viral sequences during lysogeny.
3. Lytic cycle switch with cell stress and damage e.g. UV or chemical exposure
How are viruses identified in the lab?
•Electron microscopic morphology
: Antibodies to specific proteins of different viruses
–Hybridization with specific nucleic acid probes
–Restriction digest profiles
What determines the Host range of viruses?
•Presence of specific proteins or glycoproteins on the surface of the virus particle
•Binds specific receptors on susceptible host cells
•Cellular enzymes that support viral reactions
How do you culture of viruses?
•Grow in living cells in culture
–Cell lines generated from different kinds of tissues adapted to growth in culture
–Chicken embryos or other lab animals
How is the reproduction of animal virus different from that of bacteriophage?
•1. Entry of animal virus include capsid. Just the nucleic acid in phages
–Entry methods include
•2. Uncoating of nucleic acid is necessary for the animal viruses
–In the cytoplasm (RNA viruses) or nucleus (DNA viruses)
What determines the differences if the pathways of viral multiplication?
•Multiplication cycle depends of the genetic material of the virus
•1. Type of nucleic acids
–DNA or RNA,
•2. Single stranded (ss) or double stranded (ds)3. If ssRNA, positive or negative sense
What is the cell damage by viruses?
•1. Cell death and lysis
–Persistent production of enveloped virus
•3. Transformation - altered behavior of cells
5 Types of infection by viruses
How can some virus cause cancer?
•Integration of DNA at randoms sites on host genome
–Such as tumor suppressors (cell cycle inhibitors)
–Mutated forms of cell cycle proteins or cell division activator proteins
What is the Major Immune Defense against viruses?
–Neutralization of virus attachment and hence reduce spread
–Activation of destruction by phagocytes and complement (enveloped) or NK cells
• 2. Tc or Td killing of virus infected cells - main process of virus clearance
-Prions contain protein only
-Examples of prion-caused human diseases are Kuru, Creutzfeldt-Jakob disease and Gerstmann-Straussler syndrome.
-Prions also cause scrapie in sheep.
-Bovine spongiform encephalopathy (BSE)
or Mad Cow
-Does not code for any proteins
-Replicated in cells to large amounts overwhelming host (RNA polymerase)
Hepatitis D >delta agent
human viroid disease
-enclosed in a hepatitis B virus
-simultaneous infection with
virus and the hepatitis
-D viroid causes
liver cell death
via sequestering this 7S RNA and/or cleaving it.