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Viruses and Bacteria. Antibiotics work on Bacteria, NOT Viruses!. Viruses. Protein coat Requires a host cell to replicate Smaller than a prokaryote (10-400nm) (ex. HIV, influenza/flu). Viruses binds to receptors on a cell’s plasma membrane - PowerPoint PPT Presentation
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Viruses and Bacteria
Antibiotics work on Bacteria, NOT Viruses!
Viruses
• Protein coat• Requires a host
cell to replicate• Smaller than a
prokaryote (10-400nm)
• (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 InfectionLytic 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
• Shape - 3 Shapes are most common– Cocci - round– Bacilli - rod-shaped– Spirilla - Spiral
streptococcus
Bacillus
Spirulina