Microbiology, Chapter 5, Viruses
Define Satellite viruses
* viruslike agents in human disease are defective forms, dependent on other viruses for replication.
Stages of the Lysogenic Cycle
*Attachment * Entry *Integration *Cell Division
Stages of the Lytic Cycle
*Attachment *Entry *DNA copying and protein synthesis * Assembly of new phage *Lysis
Difference between Bacteriophage & Animal Viruses
*Attachment: (B) tail fibers attach to cell wall proteins. (A) Attachment sites are plasma membrane proteins and glycoproteins *Penetration: (B) Viral DNA injected into host cell (A) Capsid enters by endocytosis or fusion *Uncoating: (B) Not required (A) Enzymatic removal of capsid proteins *Synthesis (B) in cytoplasm (A) in nucleus (DNA) or cytoplasm (RNA) *Assembly (B) Lysogeny (A) Latency; slow viral infections; cancer *Release: (B) Host cell lysed (A) Enveloped viruses bud out;noneveloped viruses rupture plasma membrane
Inactive vs. Active Viruses
Not alive/dead. Viruses don't always exhibit most life processes of, but they can direct them, more than inert molecules. Unable to replicated independently from host cell, not living things.
Virus Structure
* 20-450nm in size * Basic structure: protein shell (capsid), surrounding nucleic acid core, nucleic acid is either DNA or RNA, NOT both. Nucleic acid can be double stranded DNA, single stranded DNA, single stranded RNA, or double stranded RNA. *Lack enzymes for most metabolic process, lack machinery for synthesizing proteins. * Parasitic * Non-motile
What are the steps in Animal Viral Replication (6)
* Adsorption * Penetration * Uncoating * Synthesis * Assembly * Release
Define Cell Cultures
* Animal cell cultures are grown in sterile chambers with special media that contain the correct nutrients required by animal cells to survive.
Define Oncogenic
* Any virus capable of producing tumors
Define "in vitro"
* Cell/tissue culture methods
DNA vs. RNA Replication and Protein Production
* DNA: enter the host cell's nucleus and are replicated and assembled there. * RNA: Replicated and assembled in the cytoplasm. * Retroviruses turn their RNA genomes into DNA.
Define Prions
* Distinct protein fibrils in the brain tissue
RNA Virus Nucleic Acid Type
* Double stranded, but more often single stranded * Positive sense RNA: ready for immediate translation * Negative sense RNA: must be converted before translation can occur * Segmented * Retroviruses: carry their own enzymes to create DNA out of RNA.
Enveloped vs. Non-enveloped viruses
* Enveloped viruses merge membranes/non enveloped viruses engulf * enveloped viruses leave through budding (doesn't kill host cell). Can bud from cell membrane, nuclear envelope, or endoplasmic reticulum. * non-enveloped viruses exit through lysis (killing the cell). * enveloped take a bit of the cell membrane when they're released from host cell.
Function and Structure of Envelope
* External covering of a nucleocapsid, usually a modified piece of the host's cell membrane.
Difference between lysogenic and lytic phases
* Lytic: -Viral DNA destroys cell DNA, takes over cell functions and destroys the cell. - virus replicates and produces progeny phages - symptoms of viral infection - virtulant viral infection takes place * Lysogenic: - viral DNA merges with cell DNA and does not destroy the cell. - virus does not produce progeny - no symptoms of viral infection - temperate viral replication takes place
Define Chronic Latent Phase
* Periodically become activated under the influence of various stimuli (Herpes simplex and herpes zoster viruses).
What enzymes to viruses travel with?
* Polymerases that synthesize DNA and RNA * Replicases that copy RNA * Reverse Transcriptase synthesizes DNA from RNA
Function & Structure of Capsid
* Protein shell that surrounds the nucleic acid. (Nucleocapsid: the capsid together with the nucleic acid). Naked viruses consist of only a nucleocapsid. * Composed of identical protein subunits (capsomeres) * Capsomeres spontaneously self-assemble into the finished capsid. * Two types of capsid (helical, icosahedral)
Define Delta Agent
* Satellite virus, is a naked circle of RNA that is expressed only in the presence of the hepatitis B virus, can worsen the severity of liver damage.
DNA Virus Nucleic Acid Type
* Single stranded (ss) * Double stranded (ss) * Linear * Circular
Define Transformation
* The effect of oncogenic, or cancer-causing viruses.
Define Provirus
* Viruses that incorporate into he DNA of the host (measles virus).
Define Viroids
* Viruslike agent, differ from ordinary viruses by being very small (approx. one tenth of the size of an average virus) and composed of only naked strands of RNA, lack a capsid or any other type of coating.
Define Lysogenic Conversion
* When a bacterium acquires a new trait from its temperate phage.
Structure and Function of Spikes
* can be found on naked or enveloped viruses. * project from the nucleocapsid or the envelope * allow viruses to dock with host cells.
Define Temperate
* can participate in a lytic phase, also have the ability to undergo adsorption and penetration into the bacterial host and not undergo replication or release immediately.
Define Inclusion Bodies
* compacted masses of viruses or damaged cell organelles in the nucleus and cytoplasm.
Define Syncytia
* fusion of multiple host cells into single large cells containing multiple nuclei
Define "in vivo"
* inoculation of laboratory animals and embryonic bird tissues.
Define Tropism
* specificities of viruses for certain tissues.
Define Plaque
* the areas where virus-infected cells have been destroyed show up as clear, well-defined patches in the cell sheet.
Define Host Range
* the limited range of cells that a virus can effect
Define Induction
* virus in a lysogenic cell becomes activated and progresses directly into viral replication
Define Cytopathic Effects (CPEs)
* virus-induced damage to the cell that alters its microscopic appearance.
Intracellular Parasite (Viruses)
Can't multiply unless they invade a specific host cell and instruct its genetic and metabolic machinery to make an release new viruses