Viruses
Viruses Which Kingdom?
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.
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
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
Virus Shape and Structure: There are different shapes for viruses: 1) Helical (Spiral)
2) Polyhedral Enveloped Non-enveloped
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
VIRUS TYPES There are many virus types including: Retroviruses Reoviruses Adenoviruses Rhabdoviruses Orthomyxoviruses, etc Each has a different inner nucleic acid, coat and structure
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
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)
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)
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
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
https://www.youtube.com/watch?v=3vSRfVC4OIo
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
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
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
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
Other Viral Diseases Varicella zoster virus: chickenpox (children) and shingles (adults) Poliovirus - Polio Variola major virus: smallpox SARS coronovirus: Severe Acute Respiratory Syndrome (SARS)
Ebola: https://www.youtube.com/watch?v=sRv19gkZ4E0
Homework Read pages 52-57 #1-3, 5, 7, 8, 11-14 (p.58)