1. Viruses

2. composed of a nucleic acid (RNA or DNA) and protein coat
Very small particles that do not posess all the properties of life but can greatly affect living systems
composed of a nucleic acid (RNA or DNA) and protein coat
May also contain a phospholipid bilayer membrane (enveloped virus)
Viruses infect cells, take over transcriptional and translational machinery of the host & often kills the host

3. Virology
Study of viruses

5. Viruses probably arise by accident
DNA or RNA synthesized incorrectly and a set of genes escapes from a cell.

6. Figure 18.1 Comparing the size of a virus, a bacterium, and a eukaryotic cell

7. How big is a virus? http://cellsalive.com/howbig.htm
Viruses range in size from 20nm – 400nm and contain 5000 – base pairs of nucleic acids

8. There are 3 main shapes of viruses, although the diversity of viruses is huge and their specificity of host is very exact

9. Main shapes: Isohedral Helical - thintube
Complex – combination of shapes &/or additional structures (‘moonlanders’)

10. Viral Structure Protein coat is called a capsid
Envelope is located outside of the protein coat in some viruses
Glycoproteins-used to attach to a host cell

13. Viral Replication They are intracellular parasites
Bacteriophages-viruses that infect bacteria (Prokaryotes)
Viruses attack eukaryotic cells

14. Viruses and bacteriophages invade cells and use the host cell's machinery to synthesize more of their own macromolecules.
Once inside the host the bacteriophage or virus will either go into a Lytic Cycle -
destroying the host cell during reproduction. or
It will go into a Lysogenic Cycle - a
parasitic type of partnership with the cell

15. Attachment
The glycoproteins will attach to specific receptor proteins on the host cell
Some infect certain species or certain cells because chemical interactions control attachment

16. Injection
Virus punctures cell and its nucleic acid in the cytoplasm

17. Gene Expression
Gene expression and genome assembly proteins ‘enslave’ transcriptional and translational machinery of host, forcing its own genes to be expressed
Most viruses cause the complete shutdown of host gene expression

18. Assembly & Release
Viral genome is packed in the protein capsid and new viral particles escape the host
Enzymes that degrade host macromolecules cause cells to weaken and burst

19. The Lytic Cycle These viruses are VIRULENT because they cause disease
Lysis-cell disintegration

20. The Lytic Cycle

22. The Lysogenic Cycle
Viruses that stay in a host for a period of time go through the lysogenic cycle
They are called temperate viruses because they do not kill the host immediately
The virus DNA integrates itself with the host’s DNA
It may later enter the lytic cycle

23. The Lysogenic Cycle

25. Shingles Herpes Zoster Caused by same virus as chicken pox
Lies dormant in nervous system and is reactivated by things such as stress, immun deficiencies, or cancers

26. Smallpox Caused by several different Variola virus strains
Transmitted via person to person contact
Varies in severity
Said to be eradicated world wide b/c of vaccines

28. How does your body respond?
Immunobiology, 5th ed. Janeway

29. What are Vaccines?
A vaccine is a substance that stimulates the body’s immune response
The goal is to prevent or control an infection

31. Retrovirus Reverse transcriptase – enzyme that converts RNA to DNA
ssRNA → ssDNA → dsDNA → mRNA

32. HIV is a retrovirus

34. HIV doesn’t target just any cell, it goes right for the cells that want to kill it. “Helper" T cells are HIV's primary target. These cells help direct the immune system's response to various pathogens.

35. Click here for Life Cycle of HIV
HIV destroys the immune system by depleting T cells which protects against disease
HIV can infect 10 billion cells a day, yet only 1.8 billion can be replaced daily
After many years of a constant battle, the body has insufficient numbers of T-Cells to mount an immune response against infections. At the point when the body is unable to fight off infections, a person is said to have the disease AIDS.
It is not the virus or the disease that ultimately kills a person; it is the inability to fight off something as minor as the common cold.
Click here for Life Cycle of HIV