Exam 3 - Viruses Flashcards
What are viruses?
Non-living entities that can infect organisms of every domain
Virus particle is called what?
Virion
A virus’ structure is generally composed of what?
Nucleic acid surrounded by a protein coat
The protein coat of a virus is called _______ and is composed of _______
Capsid; capsomeres
T/F
Viral genome contains only a single type of nucleic acid (DNA/RNA) and NEVER both
True
Two types of virions
Naked - sans envelope
Enveloped - surrounded by a lipid membrane
Virion spike function
Attachment; allows virion to attach to host cell
Virus shapes (3)
Isometric
Helical
Complex
Isometric virus shape composed of:
flat surfaces forming equilateral triangles
Helical virus shape composed of:
protein coat spirals around nucleic acid; rod-shaped appearance
Complex virus shape composed of:
Isometric head with helical sheath/tail and other components
The shape of a virus is determined by its:
Capsid
Viral size is generally measured in:
nanometers
T/F
Viruses can multiply outside metabolizing cells
False
Viruses exist in two phases:
Extracellular
Intracellular
Extracellular phase, the virus is:
Metabolically inert
Acts as basic chemicals
Intracellular phase, the virus is:
metabolically active
What viral cycle occurs when viruses multiply inside the cell; also termed productive cyle
Lytic cycle
»virus lyses infected cell (kills)
What viral cycle occurs when the virus integrates into the host genome? also termed latent cycle
Lysogenic cycle
Lytic Cycle steps (5)
Attachment
Penetration
Biosynythesis
Maturation
Release
Attachment lytic step
Phage attaches baseplate to receptors and uses them for its own purpose (replication)
Penetration lytic step
Entrance of virus OR nucleic acid into host cell
Plant and bacteria viruses penetrate through the ____ _____ only
cell wall
T/F
Animal viruses enter the cell through the cell wall only
False
Animal viruses enter the cell whole (no rigid cell wall)
Penetration of the virus into animal cells is done through what process?
Phagocytosis; virus is engulfed by cell
Biosynthesis lytic step
Duplication of viral components
What 3 actions does the virus do during biosynthesis step?
Inhibit host DNA activity
Produce enzymes that destroy host DNA
Viral DNA takes over
Early synthesized viral proteins are associated with
the replication of viral nucleic acids
Late viral protein synthesization is associated with
the replication of other viral structures
Maturation lytic step
assembly of the replicated viral components into a mature virus
Release lytic step
Lysis of host cell;
releases viruses into environment
Virus is cloaked by host cell envelope
Lysogenic Cycle
replication of a dormant virus; non-productive;integrates into host DNA
Lysogenic cycle steps (4)
Attachment (same as lytic)
Penetration
Integration
Excised
Lysogenic integration:
Viral nucleic acid incorporates into host chromosome and is hidden by repressor genes/proteins
Viral DNA replicated along with host cell
Lysogenic Excision
Viral proteins repress host gene that would excise the provirus (virus integrated into host DNA),
but if host DNA is damaged;
host repair mechanisms destroy viral protein repressor;
allowing virus to excise from host DNA and return to lytic cycle
Lysogenic Conversion
Prophage can express gene coding and cause organism to display new trait
DNA Viruses replicate here
nucleus of host
RNA Viruses replicate here; and by using
cytoplasm; RNA-dependent RNA polymerase
ssRNA; + (sense) strand
Viral RNA serves as mRNA for protein synthesis and as a template for more viral RNA
ssRNA; - (antisense) strand
Viral RNA is transcribed to a + strand to serve as mRNA for protein synthesis
dsRNA
Contain both + and - strands
+ strand serves as mRNA
Replication of retrovirus
uses reverse transcriptase to produce DNA from viral genome; alters host cell’s own DNA
