Viruses are non-cellular infectious agents that are composed of nucleic acid (DNA or RNA) and protein. They have a nucleic acid core wrapped in a protein coat called a capsid. Viruses can only reproduce within host cells and do not have their own metabolism. They are grouped according to their shape, structure, type of nucleic acid, and whether they have an envelope or not. Examples of viral groups include retroviruses like HIV, rhabdoviruses like rabies, and myxoviruses like influenza.

1. Viruses Chp 21 http://www.airmanager.com/new/images/virus460.jpg

2. Viruses Viruses possess only a portion of the properties of “living” organisms Segments of DNA or RNA wrapped in a protein coat called a capsid No Metabolism Must reproduce within cells

3. Key Concepts Non-cellular infectious agents Composed of nucleic acid, DNA or RNA and protein Cytoplasm, cell membrane, etc. Nucleic acid core, protein covering, some have envelope Structure Independently by cell division Only within host cell Reproduction DNA DNA or RNA Nucleic Acid Yes Yes Mutation Yes No Metabolism Yes No Homeostasis Yes No Growth Cell Virus Characteristic of Life

4. All viruses have 2 main parts: DNA or RNA - genetic info Capsid - a protein encasement

5. Viral Shapes General Structure: Helical- rod-shaped protein coat wound helically around nucleic acid core Polyhedral- many-sided coat Enveloped- envelope around virus is made mostly of membrane remnants from previously infected cell

6. Helical Virus http://www.mcb.uct.ac.za/tutorial/virovirion.jpg , http://textbookofbacteriology.net/themicrobialworld/hsv1struc.jpg , http://www.iayork.com/Images/2008/3-10-08/AdenovirusModel.jpg Enveloped Virus Adenovirus (Polyhedral)

7. http://2.bp.blogspot.com/_aPfF45kK_Bg/RyT7ZGjngFI/AAAAAAAAAM8/eR6I9tdzafM/s320/BacteriophageCartoon.jpg http://www.brooklyn.cuny.edu/bc/ahp/LAD/C4b/graphics/C4b_TMV.GIF http://www.apositivelife.com/images/graphs/bio.jpg

8. The influenza virus has an envelope derived from the host cell. It consists of proteins, lipids and glycoproteins. The envelope helps the virus evade the host cell’s immune system.

9. Virus leaving host cell enveloped by host cell membrane

10. Grouping Viruses Grouped according to: Presence of capsid and envelope - shape RNA or DNA, single or double stranded - structure HIV Icosahedral, enveloped RNA Retroviruses Rabies Helical, enveloped RNA Rhabdoviruses Influenza A B C Helical, enveloped RNA Myxoviruses Polio, hepatitis, cancer Icosohedral, non-env RNA Picornaviruses Small pox, cow pox Complex brick, enveloped DNA Poxviruses Herpes simplex, chicken ox, mono, shingles Icosohedral, enveloped DNA Herpesviruses Resp. & intestinal infections Icosohedral, non-env DNA Adenoviruses Warts, cancer Icosohedral, non-env DNA Papovaviruses Example Shape and Structure Nucleic Acid Viral Group

11. Viral Multiplication Cycles 5 Steps Attachment Penetration Replication Assembly Release Lytic pathway Host cell lysis relatively immediate Lysogenic pathway Viral DNA integrates into bacterial chromosomes, there is a period of dormancy.

12. http://www.sciencegateway.org/resources/biologytext/cb/virus/phagerep.gif

13. http://www.accessexcellence.org/RC/VL/GG/images/examples_of_viral.gif

14. Disease Causing Viruses Emerging Viruses Viruses that evolve in a geographically isolated area and are pathogenic (disease causing) to humans Viruses and Cancer Viruses are capable of altering growth properties of humans cells they infect by triggering oncogene expression (HPV)

15. Prions and Viroids Prions Infectious protein conformations containing no genetic material. They can cause normal proteins to assume an abnormal shape preventing proper function (Mad Cow Disease) Viroids Tiny, circular molecules of RNA No protein or membrane coat Important infectious disease agents in plants