Viruses
• Virus: A noncellular particle composed
of genetic material that can invade
living cells.
– Viruses are considered by most to be nonliving since they lack metabolism and are not
made of cells.
• Are extremely small
• Are usually very specific as to what cells they can
invade
Structure of a Virus:
• Contain core of genetic information (either DNA
or RNA).
• Genetic material surrounded by a protein coat
called a capsid.
Life Cycles of viruses Lytic infection:
Infection: Virus identifies an attaches itself to a host cell. The
genetic material is then injected into the host cell.
– Growth: Genetic material of virus overrides host cell's
activities. Cell is now instructed to replicate viral genetic
material and protein coats.
– Lysis: Cell is lysed "broken open" and new viruses are released
to infect other cells. This kills the host cell
Life Cycles of viruses Lysogenic infection:
• Similar to lytic infection however important
differences exist
– Instead of immediately replicating, viral DNA
incorporates itself into the host cell's DNA.
– Will remain dormant for significant amounts of time.
– Give certain conditions, the virus will enter it's lytic
phase similar to a normal lytic infection
Retroviruses
• A new form of virus has been identified known as
a retrovirus.
– Retroviruses are RNA viruses which can conduct a
process known as Reverse Transcription
• In reverse transcription RNA is used to make DNA (the
reverse of the normal RNA transcription process).
– HIV is a retrovirus.
Virus Shapes