Viruses

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Viruses

• HIV virus
• Influenza Virus (the Flu)
• Only have ______ housed inside a PROTEIN coat.
• Requires a host cell to replicate
• Smaller than a prokaryote (10-400 nanometers)

Ebola Virus
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• Virus binds to receptors on a cells
  ________ _________
• 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.

Plasma membrane
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Lytic Cycle of a Virus

• Viruses are NOT alive!
• use the cellular machinery of another organisms
  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.

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Lysogenic Cycle of Viruses

• 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

• The virus reproduces itself, but does NOT lyse
  the cell.
• Viral DNA is injected and becomes incorporated
  into the cells DNA unknowingly.
• The inserted viral DNA is called a Provirus.

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Retroviruses (backwards)

• Instead of DNA, Retroviruses infect cells with
  RNA.
• The RNA is then copied into DNA by an enzyme
  called Reverse Transcriptase inserted as a
  prophage like the Lysogenic cycle.
• (Retro RNA to DNA instead of DNA to RNA)
• HIV is one example of a retrovirus
• Can mutate very easily and become resistant to
  treatment the problem w/ HIV

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Viruses are not always bad!

• Today, in genetic research viruses are commonly
  used.
• The viral genetic info can be removed and
  replaced with new genetic information.
• These modified viruses can then be inserted into
  other organisms, allowing the virus to inject its
  new (good) genetic info into the host cell.
• Called a Vector

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Bacterial Structure (prokaryote)

• Lacks membrane bound organelles
• Except they do have small ribosomes!

DNA is typically circular, not in chromosome form
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Identifying Bacteria

• Gram Staining stain affects bacteria
  differently based on their cell wall structure
• Gram positive purple
• Gram Negative pink
• Shape 3 different shapes are common
• Cocci
• Bacilli
• Spirilla -

Sphere shape
Rod shape
Spiral shape