1. Viruses

2. Virology: is the study of viruses.
Viruses are non-cellular entities that are parasites of cells.
Viruses consist of a nucleic acid core (DNA or RNA) surrounded by a protein coat.

3. Do viruses qualify as living things?
much smaller and less complex than cells
consist of DNA or RNA enclosed in a protein coat called a capsid
do not grow

4. no nucleus, cytoplasm, or membranes
do not carry out cellular functions.
do not generate metabolic energy.
They are obligate intracellular parasites, (they require a host cell to reproduce)

5. Anatomy of a Virus

6. The tiniest viruses are 20 nm in diameter. (smaller than a ribosome)

8. Viruses can be harmful. Virulent - disease causing
Temperate - not immediately disease causing.

9. Viruses may be helpful.
A temperate virus introduces nucleic acid from its host into a new host, changing the genetic code of the new host.
Ex. Rembrandt Tulips

10. Which organisms do viruses infect?
Some are broad based while others are not.
Swine flu virus can infect swine or humans
Rabies can infect many mammals
Some can parasitize only E. coli
Eukaryote viruses are usually tissue specific
Viruses use a “lock and key” fit to identify hosts.

11. Host range: the limited number of host species, tissues, or cells that a particular virus can infect.

12. Narrow range: AIDS virus only infects the immune system, cold virus infects the upper respiratory tract of humans

14. Broad range: rabies infects many mammalian species – rodents, dogs, humans

15. Reproduction Viruses are cellular parasites
can reproduce only within a host cell.

16. Reproduction occurs using lytic or lysogenic cycles
The Lytic Cycle
Culminates in the death of the host cell
Virulent viruses reproduce only by lytic cycle.
The Lysogenic Cycle
Replication of the viral genome without destroying the host cell.
A temperate virus may reproduce by either cycle.

17. Lytic Cycle Attachment and entry: Virus attaches itself to the cell.
Enzymes weaken the cell
nucleic acid is injected.

18. Replication: Viral DNA takes control of cell activity.
directs the host cell in replicating viral parts.

19. Assembly: All metabolic activity of the cell is directed to assemble new viruses.

20. Release: Enzymes disintegrate the cell in a process called lysis, releasing the new viruses.

21. Lysogenic cycle dormant state of a virus
does not kill the host outright right away

22. The virus injects its DNA into the cell.
The viral DNA attaches itself to the host DNA, becoming a new set of genes
May alter the cell’s traits.
May be passed to offspring.

23. The Two Cycles

24. Plant viruses
Plant viruses can stunt plant growth and diminish crop yields.
Most are RNA viruses with rod-shaped capsids produced by a spiral of capsomeres.

25. Viroids and prions are infectious agents even simpler than viruses
Viroids, smaller and simpler than even viruses
consist of tiny molecules of naked circular RNA that infect plants.
They can disrupt metabolism

27. Controlling Viruses Easy to destroy while OUTSIDE living organisms.
Inside host
Substances that destroy viruses also destroy cells
Infections in animals are very difficult to cure.

28. Vaccines There are very FEW vaccines for viral infections.
Made with inactivated or attenuated viruses.
Inactivated viruses do not replicate
Attenuated viruses have been genetically altered so they can’t cause disease
Ex. Measles, mumps, rubella, hepatitis A and B, chicken pox, smallpox and rabies.

29. Anti-Viral Drugs
Interfere with the synthesis of viral DNA or protein coats.