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By, Mackenzie Pabst. What is a Virus?  disease-causing, nonliving particle composed of an inner core of nucleic acids surrounded by a capsidcapsid 

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Presentation on theme: "By, Mackenzie Pabst. What is a Virus?  disease-causing, nonliving particle composed of an inner core of nucleic acids surrounded by a capsidcapsid "— Presentation transcript:

1 By, Mackenzie Pabst

2 What is a Virus?  disease-causing, nonliving particle composed of an inner core of nucleic acids surrounded by a capsidcapsid  A virus replicates inside living cells called host cells

3 What is a Capsid?  Outer coat of proteins that surrounds a virus' inner core of nucleic acids  The arrangement of the capsid’s proteins determine the virus' shape

4 Why are Viruses Non-Living?  Viruses are nonliving because:  They don't exhibit all the criteria for life  Criteria for life includes:  Respiration, growth and development  All viruses can do is replicate  Replication is making exact copies of themselves with the help of living cells

5 How are Viruses Named?  Some Viruses are named after the disease they cause  Example: Rabies Virus  Other viruses were named for the organ or tissue they infect.  Example: The Adenovirus effects the adenoid tissue

6 How does a Virus attach to a Host Cell?  For a virus to replicate, it must enter a host cell  When a virus’ proteins interlock with the receptor site, the virus is attached to its host cell  The attachment process is like two pieces of a jigsaw puzzle fitting together

7 Virus Attachment  Each virus has a specifically shaped attachment protein  Viruses are species specific  Some Viruses are cell-type specific  Example: polio viruses normally infect only intestinal and nerve cells.

8 Lytic Cycle: A. Attachment: The Virus attaches to the Host Cell B. Entry: The Bacteriophage injects its nucleic acid into the bacterial cellBacteriophage C. Replication : The host’s metabolic machinery makes the virus’ nucleic acid and proteins

9 Bacteriophage  Also known as a phage  Is a viruses that infects and destroys bacteria

10 Lytic Cycle: D.Assembly: New Virus Parts are made E.Lysis and Release: The host cell breaks open and releases new viruses This results in the killing of the host cell

11 Another Viral Replication Process… Of an Enveloped Virus:  After attachment, the membrane of the host cell surrounds the virus  This produces a virus- filled vacuole inside the host cell's cytoplasm.  The virus bursts out of the vacuole and releases its nucleic acid into the cell.

12 The Lysogenic Cycle

13 The Lysogenic Cycle:  Begins the same way as the Lytic Cycle  The virus attaches to the host cell and its nucleic acid is injected into the cell.  Then the viral DNA is integrated into the host cell's chromosomes  This is done instead of immediately taking over the host's genetic material (As in the Lytic Cycle)  This Cycle does not kill its host cell

14 RNA Viruses:  Many Viruses, including HIV, are RNA viruses  This means their only nucleic acid is RNA  The RNA virus with the most complex replication cycle is the Retrovirus  The Retrovirus - uses reverse transcriptase to make DNA from viral RNAreverse transcriptase  the retroviral DNA is then integrated into the host cell's chromosome

15 Reverse Transcriptase:  Is an enzyme carried in the capsid of a retrovirus that helps produce viral DNA from viral RNA  If this enzyme is found in a person, it is evidence for infection by a retrovirus

16 Retrovirus Cycle:

17  Once inside a host cell, the retrovirus makes DNA from its RNA with reverse transcriptase  Reverse transriptase produces double- stranded DNA from the viral RNA.  The double-stranded viral DNA becomes part of the host cell’s chromosome and it becomes a provirusprovirus

18 Provirus:  viral DNA that is integrated into a host cell's chromosome  It is replicated each time the host cell replicates

19 Human Immunodeficiency Virus (HIV)  HIV infects white blood cells in humans  The infected cells still function normally  Because the viral genetic material is a provirus that only produces a small number of new viruses at a time  An infected person will not appear sick  Can infect others with the virus through body fluids

20 Human Immunodeficiency Virus (HIV)  Most people with HIV will get AIDS  Over time, more white blood cells are infected and killed  White Blood cells are essential to our immune system  Their destruction reduces the body’s ability to protect itself from other viruses

21 Virus’ link to Cancer:  Some viruses have been linked to certain cancers in humans and animals  Viruses can disrupt the normal growth and division of cells in a host  This causes abnormal growth and creates tumors

22 Prions:  Are composed of proteins but have no nucleic acid to carry genetic information  Are thought to act by causing other proteins to fold themselves incorrectly, resulting in improper functioning  Responsible for many animal diseases  Example: Mad Cow Disease

23 Viroids:  Composed of a single circular strand of RNA with no protein coat  Shown to cause infectious diseases in several plants.  Have less RNA than most viruses

24 Plant Viruses:  There are more than 400 plant viruses  Plant Viruses can cause stunted growth and yield losses in their host plants.  The first virus to be identified as a plant virus was the tobacco mosaic virus

25 Plant Viruses:  Do not undergo lytic or lysogenic phases  Plant Viruses are named according to their host plant.  Not all viral plant diseases are fatal or even harmful.  The Mosaic virus, as seen in the following picture, cause patterns of color in the flowers of plants.


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