2.1 VIRUSES. 2.1 Learning Goals

Transcription

1 2.1 VIRUSES 2.1 Learning Goals To understand the structure, function, and how Viruses replicate To understand the difference between Viruses to Prokaryotes and Eukaryotes; namely that viruses are not classified as living things in taxonomy! 1

2 Major difference between viruses and bacteria: viruses are non living viruses cannot live independently outside of cells!! 2

3 A) Characteristics of Viruses Viruses are NOT living organisms Viruses are not capable of living independently outside of cells Viruses are functionally dependent on the internal workings of cells Viruses invade cells and use them as a host to function and replicate Viruses are dormant outside of cells Viruses have no cytoplasm, organelles, or cell membrane Viruses do not carry out respiration or other life processes Viruses do not grow or respond to stimuli Viruses consist of a few strands of DNA and/or RNA surrounded by a protective protein capsid 3

4 The capsid is an outer protein layer which protects the virus from attack, and allows the virus to attach to specific host cells. capsid 4

5 T4 Virus capsid end plate tail fibre T4 is a bacteriophage virus that cause E.coli 5

6 Shapes of Viruses: 6

7 B) Viral Reproduction One of the characteristics that viruses share with living things is their ability to reproduce A virus cannot do this on its own, but rather depends on the metabolism of a living cell to replicate its DNA or RNA Therefore viruses go through "replication" NOT "reproduction or mitosis /cell division"! 7

8 Two types of Viral Replication (major difference) Lytic Cycle Lysogenic Cycle immediate infection and symptoms virus DNA enters in cytoplasm of host cell will eventually flush out of body cells not activated until a later time virus DNA enters nucleus of host cell and becomes part of chromosomes indefinitely 8

9 See text p55 9

10 i. The Lytic Cycle There are 5 steps to the Lytic Cycle: 1. Attachment: A virus attaches to a specific receptor site on the cell membrane of the host cell Fits like a lock & key (or two pieces of a jigsaw puzzle) 2. Entry: Once the virus lands on the host cell, it injects its nucleic acid (DNA and/or RNA) into the host cell 3. Replication: The viral DNA and/or RNA become replicated The host cell s DNA begins to break down 4. Assembly: New virus particles are assembled 5. Lysis & Release: The host cell breaks open (lysis), and the newly formed virus is released The host cell is killed, but the new virus goes on to infect neighbouring cells and the amount of damage will vary This entire process takes approximately 30 minutes, and each time, about 200 new viruses are produced! 10

11 ... more diagrams of Lytic Cycle: 11

12 ii. The Lysogenic Cycle HIV undergoes the lysogenic cycle It is a type of RNA virus called a retrovirus Retroviruses contain an enzyme called reverse transcriptase, which causes the host cell to copy the viral RNA into the DNA The viral DNA then enters and becomes part of the host chromosomes indefinitely and is now called a provirus and the host cell lives With this technique, the viral genome is copied every time the cell divides and can continue for years even being passed on to successive generations! 12

13 See text p56 13

14 The herpes simplex virus that causes cold sores is an example of a provirus Cold sores may appear and disappear throughout someone's lifetime (the provirus is replicated as the host cell divides through mitosis, and each descendent of the host cell will carry a copy of the provirus on its chromosome) The sores appear when the viral cycle destroys cells, and they disappear when the virus is in its provirus stage It is not known what triggers it from one phase to the other? Herpes simplex 14

15 C) Viruses and Disease Viruses are small but can be deadly! Some examples The Black Plague a devastating viral pandemic that first struck Europe in the mid late 14th century ( ). It killed a third to two thirds of Europe's population. 15

16 2. The Spanish Flu Pandemic of 1918 The Influenza virus spread across the world, killing more than 25 million in six months. Caused by an unusually severe and deadly strain of the subtype H1N1 3. H1N1 Virus Swine flu outbreak of 2009 Mutated cousin of 1918 strain Killer virus high mortality Infected 30,000 people in 75 countries, usually young & healthy Was projected to infect 150 million North Americans and kill 100,000 (Pandemic) 4. The Ebola Virus Causes Viral hemorrhagic fever Current health crisis in West Africa As of Aug. 16, 2014: The World Health Organization reported 2240 suspect and confirmed cases of EV, including 1383 laboratory confirmed cases, and 1229 deaths fever 4. The HIV virus (which causes AIDS) Aids has killed ~25 million people worldwide. ~5 million new infections each year 40 million living with it currently. In 2005 alone, AIDS claimed an estimated million lives, of which more than 570,000 were children. 16

17 This is scary... Recently, prions were discovered Prions are infectious particles that cause damage to nerve cells in the brain Like some viruses, prions are not detected for many years after infection takes place Scientists discovered that prions are different to viruses though because after radiation treatment the DNA and RNA was killed off, but the infectious agent remained! 17

18 This is good... Viruses are useful tools for Genetic Engineers Because viruses enter host cells and direct the activity of the host cell's DNA If scientists want to make a copy of a positive gene, they insert it into a virus and then let the virus spread it throughout the DNA! 18

19 Genetic Biotechnology... big industry lots of future jobs! 19

20 Video #1: Amoeba Sisters v=php6iydi9ko&list=plwl0myd7dk 1FFrTjLejW YCkEO17D9TMd Video #2: How do viruses work? v=7kxhwhtghwi Video #3: 10 Most Terrifying Virus Mutations v=cwvikfk7k7o 20

21 Video #4: Hank's Top 5 Deadliest Diseases v=gf2bobjgfkg 21

22 Review & Learning Check Read p Answer Q's 1,5,9,10,11 p58 22