Viruses PDF

Viruses Biology 112  What is a Virus? Infectious particles consisting of a nucleic acid either RNA (most common) or DNA enclosed in a protein coat called a Capsid and in some cases a Lipid Envelope (like Covid 19).  Are Viruses Alive? Viruses DO NOT:...

Viruses Biology 112  What is a Virus? Infectious particles consisting of a nucleic acid either RNA (most common) or DNA enclosed in a protein coat called a Capsid and in some cases a Lipid Envelope (like Covid 19).  Are Viruses Alive? Viruses DO NOT: NO! 1. metabolize (neither anabolic or catabolic) on their own. 2. reproduce on their own. 3. consume food. 4. move (float but can’t control where they go). 5. grow. 6. have cells. Viruses DO: 1. invade cells 2. take control of the cell’s machinery 3. use that cell’s machinery for reproduction producing millions of viruses.  How does a virus find a host cell? Cells have Protein Receptors throughout their cell (plasma)membrane. Viruses have additional proteins on their capsid called Ligands that bind to the cells protein receptors that enable a virus to enter a host cell. Viruses are highly specific to the cells they infect: 1. Plant viruses infect plant cells. 2. Animal viruses infect animal cells. 3. Bacterial viruses (Bacteriophages) infect bacterial cells. Bacteria / Plant / Animal Viruses  Bacteriophages The video below shows how bacteriophages are very beneficial to our survival: https://www.youtube.com/watch?v=YI3tsmFsrOg  What does the virus do after it binds? Once the virus has bound to the host cells, it injects the cell with it’s viral genome (RNA or DNA).  A virus can reproduce in two ways Lytic Cycle Lysogenic Cycle They infect & affect the They infect & lay dormant host cell very quickly. before affecting the host. The virus enters a cell, The virus integrates its makes copies of itself, and DNA into the DNA of the causes the cell to burst. host cell, and the viral genetic information Examples: Rabies, Measles, replicates along with the Influenza, Hepatitis host cell's DNA. Examples: Mumps, HIV, Herpes, Chicken Pox  Retroviruses Are special types of RNA based viruses. As soon as it infects the cell a retrovirus makes a DNA copy of their RNA. This DNA is inserted into the DNA of the host cell. In all prokaryotic & eukaryotic cells RNA is made from DNA but in a retrovirus its genetic information is copied backward using an enzyme called reverse transcriptase from RNA to DNA. Example: HIV, COVID 19  Examples of Viruses Small Pox Encephalitis Chicken Pox Influenza Herpes Meningitis Hanta Ebola Mumps HIV Measles Rubella Polio Mononucleosis Hepatitis A, B. & C Rabies West Nile HPV Corona Yellow Fever Covid 19 H1N1 (Swine Flu)  CORONA VIRUS (COVID 19) Video: https://www.youtube.com/watch?v=BtN-goy9VOY  Vaccines Vaccines are used to establish immunity. Discovered by Edward Jenner (Small Pox vaccine 1796) They can be made of weakened viruses or viruses who had their nucleic acid (either RNA or DNA) removed. The body recognizes and destroys the viruses. It will “remember” them so that the next time they are in the body, they will be destroyed. Ex. The H1N1 Shot  Viroids and Prions Viroids are: Infections agents composed of a single, circular strand of RNA. They are not protected with a protein coat. Viroid RNA does not code for any known protein. Mostly affect plants but recently have been found to affect humans. Example: Hepatitis D  Viroids and Prions Prions are: An infectious particle made of protein. Affect the brain or neural tissue. All are untreatable and fatal. Examples: Mad Cow Disease (Bovine Spongiform Encephalopathy) & Creutxfeldt – Jakob Disease (CJD)  NOT ALL VIRUSES ARE NASTY ! Today in biology, viruses are used as vectors. A Vector is a genetically altered virus that transports a good gene (DNA) into a cell that needs it. Scientists construct DNA sequences that code for a desired gene in an organism and then infect a virus with this DNA. The virus is then allowed to contact the cell that’s missing the gene required to survive or improve its successfulness. The virus infects the cell and incorporates its DNA into the host’s DNA. Now the host cell has access to the desired gene. This whole process is part of Gene Therapy.