Viruses, Viroids, and Prions

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Transcript Viruses, Viroids, and Prions

Viruses, Viroids, and Prions

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Are Viruses Living or Non-living?

Viruses are NOT considered living.

They have some properties of life but not others They can’t maintain a constant internal state (homeostasis).

They are not made up of cells.

They cannot reproduce by themselves.

They do not metabolize .

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What are Viruses?

A virus is a non cellular particle made up of genetic material and protein that can invade living cells.

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Viral History

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Discovery of Viruses

Beijerinck (1897) coined the Latin name “virus” meaning poison

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Tobacco Mosaic Virus Wendell Stanley (1935) crystallized sap from sick tobacco plants of He discovered viruses were made nucleic acid and protein

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Smallpox Edward Jenner (1796) milder developed a smallpox vaccine using cowpox viruses Deadly viruses are said to be virulent Smallpox has been eradicated in the world today

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Viewing Viruses Viruses are Measured in nanometers seen until the smaller than the smallest cell Viruses couldn’t be electron microscope invented in the century was 20 th

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Size of Viruses

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Viral Structure

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Characteristics Non living structures Noncellular Contain a protein coat called the capsid Have a nucleic acid core containing DNA or RNA Capable of reproducing only when inside a HOST cell

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Viral Structure Some viruses are enclosed in an protective envelope spikes that surrounds the capsid. It helps the virus enter the cell.

Some viruses may have to help attach to the host cell Most viruses infect only SPECIFIC host cells DNA CAPSID ENVELOPE SPIKES

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Outside of host cells, viruses are enzymes metabolism Use the reproduce inactive Lack ribosomes and needed for raw materials and enzymes of the host cell to be able to HIV VIRUS EBOLA VIRUS

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Disease causing viruses Some viruses cause disease Smallpox, measles, mononucleosis, influenza, colds, warts, AIDS, Ebola Some viruses may cause some cancers like leukemia Virus-free cells are rare MEASLES

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Viral Shapes Viruses come in a variety of shapes Some may be helical shape like the Ebola virus Some may be polyhedral shapes like the influenza virus Others have more complex shapes like bacteriophages

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Helical Viruses

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Polyhedral Viruses

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Complex Viruses

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Herpes Virus SIMPLEX I and II

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Adenovirus COMMON COLD

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Influenza Virus

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Chickenpox Virus

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Papillomavirus – Warts!

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Used for Virus Identification RNA or DNA Virus Do or do NOT have an envelope Capsid shape HOST they infect

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Bacteriophages

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Bacteriophages Viruses that attack bacteria are called bacteriophage T-phages are a specific class of bacteriophages with polyhedral heads , double-stranded DNA , and tails Inject viral DNA cell into

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Escherichia Coli

Bacterium T-PHAGES ATTACK THIS BACTERIUM

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Retroviruses

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Retroviruses Contain RNA , not DNA HIV, the AIDS virus, is a retrovirus Feline Leukemia Virus is also a retrovirus

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Viroids & Prions

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Viroids Small, circular RNA coat molecules without a protein Infect famine plants Ex: Potato in Ireland

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Prions

Prions are “infectious proteins” They are normal body proteins that get converted into an alternate configuration proteins They have by contact with other prion no DNA or RNA

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Prion Diseases Prions form insoluble deposits in the brain Causes neurons to rapidly degenerate.

Mad cow disease (bovine spongiform encephalitis: BSE) is an example People in New Guinea used to suffer from kuru , which they got from eating the brains of their enemies

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Viral Replication

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Viral Attack Viruses are very specific as to which species they attack HOST specific Viruses will enter either a lytic or lysogenic cycle within the host cell.

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4 Steps of Lytic Cycle 1. Attachment to the cell 2. Penetration (injection) of viral DNA or RNA 3. Replication & assembly of new viruses 4. Release of the new viruses into the environment (the cell lyses or bursts)

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Viral Latency Some viruses have the ability to become dormant inside the cell Called latent viruses They may remain inactive for long periods of time (years) Later, they activate to produce new viruses HIV and in response to some external signal Herpes viruses are examples

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Lysogenic Cycle Latent viruses stays inside cell, but do not kill the cell. Viral DNA integrates with host DNA Host cell divides normally Can eventually enter the , therefore new cells are infected with virus lytic cycle & kill cell

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The Lytic & Lysogenic Cycle

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Latency in Humans Some eukaryotic viruses remain dormant for many years in the nervous system tissues Chickenpox (caused by the virus

Varicella zoster

) is a childhood infection It can reappear later in life as shingles , a painful itching rash limited to small areas of the body SHINGLES

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Latency in Humans Herpes viruses also become latent in the nervous system A herpes infection lasts for a person’s lifetime Genital herpes Simplex 2) (Herpes Cold sores or fever blisters (Herpes Simplex1) SKIN TO SKIN CONTACT PASSED AT BIRTH TO BABY

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Virulence VIRUS DESTROYING HOST CELL

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Treatment for Viral Disease

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Vaccines An attenuated virus is a weakened, less vigorous virus “Attenuate" refers to procedures that weaken an agent of disease (heating) A vaccine against a viral disease can be made from an attenuated, less virulent strain of the virus Attenuated virus is capable of stimulating an immune response and creating immunity, but not causing illness

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