01 Virology Flashcards
Why are viruses non-living?
cannot carry out independent metabolic activity
cannot reproduce independently
==> obligate intracellular parasites
How large are viruses?
~20-300nm
In what form is viral genetic information?
either DNA or RNA
in either single stranded or double-stranded form
either linear, circular or segmented
(all exist!)
How many genes do viruses have?
3-100
What is a capsid?
Capsid = protein coat; surrounds viral genetic material
Made of capsomere units (different for each virus)
What is a viral envelope?
Acquired from host plasma membrane during exocytosis
Phospholipid bilayer
Mix of host and viral membrane proteins/glycoproteins
What is a viral host range?
The range of host cells that a virus can attach itself to
SEQ the lytic cycle
Virus binds to host cell for which it has appropriate recognition
Viral genome enters cell - either injected, via endocytosis, or via fusion with host cell plasma membrane
Viral genome directs protein production; copies viral genome and proteins using cell resources
Viral nucleic acids and capsomeres spontaneously self-assemble
Virus destroys host cell plasma membrane with lytic enzymes => virus exits, host cell dies.
What defenses do bacteria have against viruses?
Some do not have surface receptors recognized by virus => no attachment
Some have restriction enzymes - recognize, destroy foreign DNA while bacterial DNA is protected by methylation
SEQ the lysogenic cycle
Phage attaches to host cell, injects DNA
Forms circle of viral DNA which is incorporated into specific site on host chromosome == ‘prophage’, integrated virus
Virus replicated during standard cell replication until environmental changes trigger reversion to lytic cycle
What is a temperate phage?
A phage with either lytic or lysogenic replication
What is a bacteriophage?
A phage that parasitizes bacteria
What is a virulent phage?
A phage with lytic replication
What is phage lamda?
A temperate phage
