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Viruses - PowerPoint PPT Presentation

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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. Virus binds to receptors on a cell’s \_\_\_\_\_\_\_\_ \_\_\_\_\_\_\_\_\_

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Presentation Transcript
  • 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

Virus binds to receptors on a cell’s ________ _________
    • 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

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.

Lytic Cycle of a Virus
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

Lysogenic Cycle of Viruses
retro viruses backwards
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
viruses are not always bad
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
bacterial structure prokaryote
Bacterial Structure (prokaryote)
  • Lacks membrane bound organelles
  • Except they do have small ribosomes!

DNA is typically circular,

not in chromosome form

identifying bacteria
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