1. Viruses
TEK 4C:
Compare structures of viruses to cells, describe viral reproduction, and describe the role of viruses in causing diseases such as HIV and Influenza

2. Virus Structure
A virus particle, or virion, consists of the following:
Nucleic acid - genetic instructions, either DNA or RNA
Protein coat (capsid) - Surrounds the DNA or RNA; for protection of genetic material
Lipid membrane - Surrounds the protein coat (found only in some viruses, including influenza)
These types of viruses are called enveloped viruses as opposed to naked viruses

3. Bacteriophage: viruses that infect only bacteria.
Bacteriophage Structure:
Bacteriophage: viruses that infect only bacteria.
Have a protein "tail" attached to the capsid which is used to infect the host bacteria.
Animal Virus Structure:
Surface Proteins – also called glycoproteins, found outside the capsule, aid in attachment to host cells.

4. Structure: Virus vs. Cell
Can you answer the following questions? ?

5. Specificity: To Host Cells
Viruses are specific to their hosts.
They can only attach to specific cells at receptor sites using the glycoprotein projections.
Rabies can be passed from animal to human.
Influenza is a virus that specifically attacks cells of the respiratory tract (leading to coughing, sneezing, and sniffling).
HIV virus specifically attacks white blood cells (helper T cell). HIV is a virus that seems specific to humans.

6. Viral Reproduction
Viruses use their own genetic material and the host cell's machinery.
Penetration - surface proteins bind to host, and release genetic material (RNA or DNA) into the cytoplasm
Replication - the viral genetic material is copied
Protein synthesis - viral proteins (parts) are made
Viral Assembly – new virions are put together
Release - viruses emerge from the cell by "budding" from the cell membrane or bursting out of the cell (this causes the cell's death)
*A virus is considered to have quick replication when symptoms emerge within the first 2 weeks (1-14 days) of contracting the virus.

7. Lytic vs. Lysogenic Reproduction
Lysogenic Pathway - the virus stays within the cell until certain environmental triggers cause it to enter the lytic cycle
Lytic Pathway - rapid replication of the virus, ending in cell lysis (bursting and cell death). More phages are released to infect other cells.
Which of the following videos is depicting the lysogenic cycle? Which is the lytic cycle?

8. Role of Viral Disease & Prevention
A pathogen is a disease causing agent, such as bacteria, viruses, fungi or parasites.
Prevention: vaccines.
Vaccine: a substance used to stimulate the production of antibodies and provide immunity against one or several diseases.
Treatment: anti-viral medications. You cannot treat a virus with antibiotics!
HIV
HIV will slowly reduce the number of T-cells until the person develops Acquired Immunodeficiency Syndrome (AIDS).
Most commonly, people get or transmit HIV through sexual contact and needle or syringe use.
Influenza
Most experts think that flu viruses spread mainly by droplets made when people with flu cough, sneeze or talk.

9. QR Quiz