Download Viruses and Bacteria

Viruses and Bacteria
Antibiotics work on Bacteria, NOT
Viruses!
Viruses
• Protein coat
• Requires a host
cell to replicate
• Smaller than a
prokaryote (10400nm)
• (ex. HIV,
influenza/flu)
• Viruses binds to receptors
on a cell’s plasma
membrane
– Viruses are organism
specific because of these
receptors!
– Viruses have attachment
proteins on their surface.
– Examples – a plant virus
cannot infect an animal cell,
a T4 Bacteriophage cannot
infect a skin cell
Viral Infection
Lytic Cycle of a Virus
• Viruses are NOT alive!
– use the cellular machinery
of another organism’s
living cells to multiply
themselves
• Tail of the virus attaches
to host
– injects its DNA or RNA
into the host.
• Host cell cannot tell the
difference between its
own DNA and that of the
virus
• Cell replicates the viral
DNA as if it were its own.
• Thousands of copies of
the viral DNA and protein
coat are made.
• Eventually the cell
becomes too full and
lyses (bursts) releasing
hundreds of virus
particles that can now
infect other cells.
Lysogenic Cycle of Viruses
• The virus reproduces
itself, but does NOT
lyse the cell.
• Viral DNA is injected
and becomes
incorporated into the
cell’s DNA
unknowingly.
• The inserted viral DNA
is called a Provirus.
• The virus can remain
inactive like this for
long periods of time
– When the cell replicates,
so does the virus!
• Sudden changes
(temperature or
availability of food)
may cause the DNA of
the prophage to
become active.
• Now new viral DNA
could be synthesized
like in the Lytic cycle
Retroviruses (backwards)
• Instead of DNA, Retroviruses infect cells
with RNA.
– RNA is then copied into DNA by an enzyme
called Reverse Transcriptase and inserted as
a prophage like the lysogenic cycle.
– HIV is a retrovirus
– Retroviruses mutate very easily, making them
resistant to treatment - the problem with HIV
Viruses are not always bad!!
• Viruses are commonly used in genetic research.
– The viral genetic info can be removed and replaced with new
genetic information
– These modified viruses - called vectors - can then be
inserted into other organisms, allowing the virus to inject its
new (good) genetic info into the target cell.
Bacterial Structure (prokaryote)
• Lacks membrane
bound organelles
• Except they do
have small
ribosomes!
DNA is typically circular,
not in chromosome form
Identifying Bacteria
• Gram Staining - Stain
affects bacteria
differently based on
their cell wall structure
– Gram positive = Purple
– Gram negative = Pink
streptococcus
Bacillus
• Shape - 3 Shapes are
most common
– Cocci - round
– Bacilli - rod-shaped
– Spirilla - Spiral
Spirulina