1. Virology - study of viruses
Objective: G2 - Describe viral structure, reproduction, & the role of viruses in causing diseases, and compare the structure of viruses to cells
Virology - study of viruses
tiny, much smaller than a cell and only visible with advanced electron microscopes;

2. Discovery of Viruses
Edward Jenner (1796) developed smallpox vaccine using milder cowpox viruses
Beijerinck (1897) coined the Latin name "virus"  meaning poison
Wendell Stanley (1935) crystallized sap from tobacco leaves infected with a virus & found virus was made of nucleic acid & protein
Viruses couldn't be seen until the electron microscope was invented in the 1930s
tiny, much smaller than a cell and only visible with advanced electron microscopes;

3. Viral Characteristics
Non living
Not made up of cells
Cannot grow or replicate on their own
Must be reproduced in living cells

4. Can ONLY reproduce inside of a living host cell
Some can cause disease (smallpox, measles, mononucleosis, influenza, colds, AIDS, Ebola)

5. Highly host specific (only infect certain cells)
Viruses are classified into 2 main groups by their nucleic acid --- DNA or RNA Viruses

6. Viral Structure
Consist of a nucleic acid core (DNA or RNA) and a protein coat called the capsid that allow them to identify a specific type of cell and attach to it
Lack ribosomes & enzymes needed for protein synthesis or metabolism

7. Bacteriophage ----
– viruses that infect bacteria
HIV 
- attacks T-cells of the human immune system

8. Virus Replication
Viruses cannot reproduce on their own, and must infect a host cell in order to create more viruses.

9. Viruses use their own genetic material and the host cell's machinery
1. Penetration - surface proteins bind to host, and release genetic material (DNA or RNA) into the cytoplasm
2. Replication - the viral genetic material is copied
3. Transcription - the genetic material is used as a blueprint, for the cell to make messenger RNA which is used to make viral proteins
4. Protein synthesis - occurs in the cytoplasm (ribosomes), viral proteins are made
5. Viral Assembly - the viral genetic material (from replication) is surrounded by the newly made viral proteins
6. Release - viruses emerge from the cell by "budding" from the cell membrane or bursting out of the cell (this causes the cell's death)
Viruses are about a thousand times smaller than bacteria

10. Lysogenic Cycle
Lysogenic Pathway - the virus stays within the cell until certain environmental triggers cause it to enter the lytic cycle
the virus stays within the cell until certain environmental triggers cause it to enter the lytic cycle

11. Lytic cycle
Lytic Pathway - rapid replication of the virus, ending in cell lysis (or death). More viruses are released to infect other cells
lytic cycle (see figure above):
A virus particle attaches to a host cell.
The particle releases its genetic instructions into the host cell.
The injected genetic material recruits the host cell's enzymes.
The enzymes make parts for more new virus particles.
The new particles assemble the parts into new viruses.
The new particles break free from the host cell.

12. Human Immunodefiency Virus (HIV) - causes AIDS
Retrovirus - RNA inside a protein coat
HIV infects one particular type of immune system cell, called a T-helper cell that functions in the body’s immune response.
Once infected, the T-helper cell turns into a HIV-replicating cell.
There are typically 1 million T-cells per one milliliter of blood. HIV will slowly reduce the number of T-cells until the person develops AIDS.

13. Check for Understanding
NO !!!
1. Are viruses alive? _________
2. Why or why not? ________________________
3. Can viruses reproduce on their own? _______
4. What do viruses need in order to reproduce?
_________________________
Not made up of cells No
A host cell

14. 5. Structurally, what do viruses have in common with living things
6. What type of cell do bacteriophages attack? ________________
7. Which body system do T-cells belong to? ________________
Genetic information
bacteria
Immune