Viruses & Disease Chapter 19.2 Herpes virusEbola virus

Discovery of Viruses 1. In Russia, Dmitri Ivanovsky was asked to investigate a disease affecting tobacco plants. 2. He found juice from one plant infected other plants, even when passed through fine filters. 3. He found no cells in this “juice” and concluded that the disease was caused by a “poison”. 4. Later it was suggested that the infecting agent was a very tiny particle. 5. One scientists isolated virus crystals inferring that these virus particles were not living. Slide # 2

How Small is a Virus? Slide # 3

Viruses are 1/1000 to 1/10,000 the size of our cells. Slide # 4

What is a Virus? 1. contain DNA or RNA 2. are not cells 3. are non-living particles 4. do not have a metabolism 5. can not reproduce on their own (-the infected host cell reproduces the virus particles) 6. are parasites that can cause disease Slide # 5

Bacteriophage virus Tobacco Mosaic Virus Cold virusFlu virus How are Viruses Classified? 1.Type of nucleic acid: DNA or RNA 2.Shape of Protein Coat (called a Capsid) Capsid Slide # 7

3. Retrovirus a. Class of RNA viruses that changes its RNA into DNA when injected into a host cell. b. Contains reverse transcriptase enzymes. c. Example of a Retrovirus is HIV the virus that causes AIDS. Slide # 8

How do Viruses Work? 1. Viruses use a host cell to reproduce: The virus must inject their genetic material into a host cell, so it can instruct the host cell to make new virus particles. 2. Viruses are specific to the type of cell it can infect. Ex. The Hepatitis virus only infects liver cells. Ex. The Hepatitis virus only infects liver cells. Ex. HIV only affects Helper T cells (type of immune system cell) Ex. HIV only affects Helper T cells (type of immune system cell) Ex. A bacteriophage virus… Ex. A bacteriophage virus… Slide # 9

Ex. A Bacteriophage virus only infects Bacteria are destroyed as viruses break out. E. coli Bacteriophage BACTERIA. Slide # 10

Empty capsids litter this infected bacterium’s cell wall. Viral Capsids (protein coat) Where is the viral genetic material?  inside the bacteria Slide # 11

3.A Virus is specific in the type of cell it invades because it attaches to specific binding sites called Receptors on the host cell. Host Virus Receptors on the host cell have a similar shape to the virus. Slide # 12

Hijacking a Host Cell to Reproduce 1. The virus attaches to a receptor on the host cell. 2. Genetic info is inserted into the host cell. 3. Host Cell is forced to make virus genetic material (DNA or RNA) and proteins (capsid). 4. Viruses are assembled (put together). 5. New virus particles break out of the host cell killing it. *(Some viruses bud out without destroying the host cell. -ex. HIV) *(Some viruses bud out without destroying the host cell. -ex. HIV) Slide # 13

Viral reproduction occurs immediately and host cell death in most cases. Lytic Cycle: Slide # 14 Animation Link

Bacteriophage enzyme lyses the bacterium’s cell wall, releasing new bacteriophage particles that can attack other cells. Bacteriophage proteins and nucleic acids assemble into complete bacteriophage particles Bacteriophage takes over bacterium’s metabolism, causing synthesis of new bacteriophage proteins and nucleic acids Bacteriophage injects DNA into bacterium Bacteriophage attaches to bacterium’s cell wall Bacteriophage Bacteriophage DNA Bacteriophage protein Bacteriophage protein coat Bacteriophage DNA Bacterial chromosome Lytic Cycle Slide # 15 Viral Reproduction: The Lytic Cycle Go to Section:

Lysogenic Cycle: Viral DNA hides out by inserting itself into the host DNA.Viral DNA hides out by inserting itself into the host DNA. Prophage (or Provirus): viral DNA that has been inserted into the host’s DNA.Prophage (or Provirus): viral DNA that has been inserted into the host’s DNA. It may lay dormant (inactive) for a period of time or it may periodically release a few viruses (switches to lytic cycle). It may lay dormant (inactive) for a period of time or it may periodically release a few viruses (switches to lytic cycle). Slide # 16 Animation Link

Bacteriophage proteins and nucleic acids assemble into complete bacteriophage particles Bacteriophage enzyme lyses the bacterium’s cell wall, releasing new bacteriophage particles that can attack other cells Bacteriophage DNA inserts itself into bacterial chromosome Bacteriophage DNA (prophage) may replicate with bacterium for many generations Bacteriophage DNA (prophage) can exit the bacterial chromosome Bacteriophage DNA forms a circle Bacteriophage DNA Bacterial chromosome Bacteriophage injects DNA into bacterium Prophage Lytic Cycle Lysogenic Cycle The Lysogenic Cycle Go to Section: Slide # 17

Lytic and Lysogenic Cycles of Reproduction Pg. 481

Resources  Mysterious Invaders Mysterious Invaders Mysterious Invaders  Virus Information and pictures Virus Information and pictures Virus Information and pictures  Lytic Cycle Animation Lytic Cycle Animation Lytic Cycle Animation  Can you get AIDS from a mosquito bite? Can you get AIDS from a mosquito bite? Can you get AIDS from a mosquito bite?  HIV Infection animation HIV Infection animation HIV Infection animation The HIV Virus