1. Viruses

2. Brain Tap
What do we already know about Viruses?

3. Virus Research Project
With your lab partner, you will work together to create a “Virus Wanted Poster”
With your partner, pick a Virus you are interested in researching (first come, first serve)
Tentative due date:Monday Oct 26

4. The impact of Viruses
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5. So what are viruses? Are they living?
Characteristic of Life
Virus
Cell
Growth NO
YES
Homeostasis
Metabolism
Mutation
Nucleic Acid
DNA or RNA
DNA
Reproduction
Within Host Cell
Cell Division
Structure
Nucleic acid core, protein covering.
Cytosol, cell membrane, organelles

6. Viruses
Submicroscopic obligate, intracellular parasites… but are typically considered NON-LIVING (do not meet all the requirements that make life)
Submicroscopic: Extremely small particles, unable to view using light microscope
Can sometimes be seen using powerful electron microscopes
Range in size from 20nm to 250nm (the size of a bacterium)

7. Viral Structure
All Viruses have two essential features: A nucleic acid, and a protein coat surrounding it.
Nucleic acids: Can be either DNA or RNA
Nucleic acid: Can be helical, closed loop, or long strand, depending on the virus.
The Protein Coat surrounding the virus is known as the capsid.

8. Viral Structure Cont’d
Some viruses have a membrane-like structure on the outside, known as an envelope.
Envelope is made mostly of lipids (fats) from the host cell, and aids in the infection of host cells.
On the surface of the envelope, are projections made of Glycoproteins
Projections made of sugar chains, which help the virus attach to the host cell

9. Not listed: Spherical viruses (e.g. Influenza)

10. Grouping Viruses
The grouping of viruses is based on the presence of a capsid structure, envelope, and the nucleic acid type they contain.
Table 25-2 In your textbook

11. DNA Viruses Directly produce RNA, then make Viral proteins
Viral DNA joins host cell DNA, and directs protein synthesis from there
(More on this during Viral Replication)

12. RNA Viruses
Viral RNA is released into the host cytoplasm, where it directly links up with ribosomes, to produce Viral proteins

13. Retrovirus Example: HIV
Contain an enzyme known as Reverse Transcriptase
Reverse Transcriptase – Uses Viral RNA as a template to make DNA, which is then integrated into the host genome, replicates like a DNA virus.
Named so because it reverses the transcription process (RNA  DNA)
Example: HIV

14. Viroids and Prions Simpler forms of Viruses
Viroids – Smallest known particles capable of replicating, consisting of a short, single strand of RNA.
Prions – Abnormal clumps of proteins, blocks normal cell traffic, killing the cell. Mad Cow disease is caused by a Prion virus.

15. To Do Now
Work on 25.1 Review