Download Viruses - Granbury ISD

Viruses
Living or Not
Virus
• Virus – small
particle made of
1. Nucleic acids
either DNA or
RNA
2. Surrounded by a
protein coat
Virus
• Viruses are smaller
than the tiniest
bacterium.
• They are not
considered to be
alive:
1. Don’t grow or
develop
2. Don’t carry on
respiration
3. They can’t
reproduce on their
own
Virus Structure
• The outer protein
coat is called the
capsid.
• This capsid gives
the virus its shape.
• The protein
arrangement
determines what
cell can be
infected.
Virus
Virus
• Every virus has a
specially shaped
device call an
attachment
protein
• Each virus can only
attach to a few
kinds of cells
• This process is like
two pieces of a
jigsaw puzzle
Viral Replication Cycles
• A virus must
infect a host cell
to replicate.
• Once inside the
virus takes over
the cell
metabolism.
Viral Replication Cycles
• 2 ways for a
virus to enter a
cell.
1. Virus nucleic
acid is injected
into the cell.
Viral Replication Cycles
2. Virus is
surrounded by
plasma
membrane and
taken into the
cell cytoplasm.
This vacuole will
burst releasing
the virus.
Lytic Cycle
• Once inside, the
virus takes over
the cell processes.
• The cell enzymes
and energy are
used to make more
viruses.
• The cell will burst
releasing the
viruses.
• Lysis – bursting of
a cell.
Lytic Cycle
• The new viruses
infect more
cells.
• This active
process of
making more
viruses is called
a lytic cycle
Lysogenic Cycle
• Lysogenic cycle – replication cycle
where the viral nucleic acid is
incorporated in the cell DNA.
• This new DNA is called a provirus
Lysogenic Cycle
• The cell carries out its own functions.
• Every time the cell replicates, it copies the
viral DNA.
• This resting phase can last for many years.
• At any time, the
provirus can be
activated and
enter a lytic cycle.
• When this
happens, the virus
will replicate and
kill the cell.
• Examples:
Herpes simplex I
Hepatitis B
Chicken pox
Lysogenic
cycle
Retrovirus
• Retrovirus – a virus
with RNA as its
nucleic acid.
• It must work
backwards making
DNA from RNA
• The enzyme used is
called Reverse
transcriptase
• HIV is a retrovirus
BREAKING NEWS !
• Papiloma virus
causes cancer!!!
• HPV has been shown
to cause cervical
cancer
• Other viruses are
being studied as
possible causes of
cancer.(that means
tumors)
Illnesses caused by viruses
• Cold
• Flu
• Chicken Pox
• Measles
• Mumps
• Polio
• HIV AIDS