1. Viruses

2. Viruses
Which Kingdom?

3. Viruses They are considered “lifeless”…why?
They can NOT carry out metabolic and reproductive functions alone.
They require a host organism
They lack cytoplasm, organelles, and a cell membrane
5000 influenza viruses can be found on the head of a pin.

4. Viral Infections Are they all deadly?
No, viruses range from mild to deadly
Ex. Herpes simplex I, West Nile Virus, cold/flu viruses, Cancer, HIV/AIDS.
Each virus is specific to a host
The host range describes all of the hosts a virus can infect
E.g. swine flu virus infects both pigs and humans

5. Scientists classify viruses based on their unique characteristics, including:
size and shape of the capsid (protein coat
surrounding genetic material)
shape and structure of the virus
type(s) of diseases the virus causes
type of genetic material (RNA or DNA)
method of reproduction

6. Virus Shape and Structure:
There are different shapes for viruses:
1) Helical (Spiral)

7. 2) Polyhedral
Enveloped
Non-enveloped

8. 3) Complex/Phage (many sides with a tail)
E.g. Bacteriophage (bacteria eating virus)
An inner genetic material (nucleic acid - DNA or RNA)
Capsid – outer protein coat

9. VIRUS TYPES There are many virus types including: Retroviruses
Reoviruses
Adenoviruses
Rhabdoviruses
Orthomyxoviruses, etc
Each has a different inner nucleic acid, coat and structure

11. Methods of Reproduction
Incubation period = the time it takes between when the virus infects a cell and when symptoms appear (when the virus ruptures the cell).
There are two types of reproduction/replication:
 The LYTIC cycle – shorter incubation period
 The LYSOGENIC cycle – longer incubation period

12. How Do Viruses Replicate?
Viruses replicate through a cycle known as the lytic cycle
Some viruses, such as cancer causing viruses and bacteriophages, go through a lysogenic cycle
Occurs without the host being aware and the host may not be aware until years later (e.g. HIV)

13. Lytic Cycle The lytic cycle occurs through four steps:
Attachment and entrance: the virus recognizes the host cell and then enters into the cell’s cytoplasm
Synthesis of protein and nucleic acid: The virus tricks the cell into copying the virus DNA (or RNA)

14. How Do Viruses Replicate?
Virus replicates through four steps:
Assembly of the virus: All the virus components (i.e. DNA (or RNA), enzymes, capsid proteins, and other proteins are brought together
Release of new viruses: the new viruses burst out of the cell in a process known as lysis

15. Lysogenic Cycle
The virus enters the cell just as the lytic cycle, but instead of it replicating, its nucleic acid becomes part of the cell’s nucleic acid
When the cell replicates, so does the virus nucleic acid

17. Viruses and Human Health
Viruses destroys cells as they replicate  This causes the symptoms
Vaccines are used to prevent virus infection
Vaccines: are made of dead virus or virus components to activate the body’s immune cells to prepare them for battle

18. VIRUSES AND CANCER
Some viruses can cause cancer by adding specific genes to an infected cell transforming it into a cancer cell
Virus
Cancer Type
Human papillomavirus
Cervical, skin, etc.
Hepatitis B/C
Liver cancer, lymphomas
Epstein-Barr virus
Burkitt’s lymphoma, Hodgkin’s lymphoma

19. INFLUENZA VIRUS
Various strands of the flu virus exist in the environment
Flu Vaccines only treat the most common strain of the season
Virus destroys cells in upper respiratory tract so there is no sweeping of foreign particles
Symptoms – sore throat, congested lungs

20. Human Immunodeficiency Virus (HIV)
Virus that causes AIDS (Aquired Immunodeficiency Syndrome)
Retrovirus is transmitted through variety of bodily fluids: blood, semen, vaginal fluid, breast milk
HIV attacks the immune system
Since 1981, almost 25 million people have died from AIDS

21. Other Viral Diseases
Varicella zoster virus: chickenpox (children) and shingles (adults)
Poliovirus - Polio
Variola major virus: smallpox
SARS coronovirus: Severe Acute Respiratory Syndrome (SARS)

22. Ebola: https://www.youtube.com/watch?v=sRv19gkZ4E0

23. Homework
Read pages #1-3, 5, 7, 8, (p.58)