Download Viruses

Viruses
• Are obligate intracellular parasites
• Some are small as ribosome
• Some bigger than some bacteria
All contain a sort of genetic
material
Could be DNA (single or double stranded)
Could be RNA (single or double stranded)
All contain a protein coat enclosing the
genetic material=capsule
Some have a viral envelope that is derived from a host cell
membrane
BACTERIOPHAGES (Phage) are the best understood viruses
An example of a phage is the T4 phage
Its life cycle always results in the
death of host cell
This cycle is called the lytic cycle
If this is the only life cycle the phage is a virulent
phage
Viral life cycles
Lysogenic cycle
-temperate phages
-DNA is incorporated into
host genome
-called prophage
-may enter the lytic cycle
-environmental triggers
Viral envelopes
Have glycoproteins that help bind
to cell membrane
Capsid enters cell
Genetic material copied
New capsid proteins made
Glycoproteins produced in ER
Viruses bud out of cell
Retroviruses
Single stranded RNA
that acts as template
for DNA