Viruses

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Viruses

• What is a virus?
• Terminology
• Characteristics of a virus
• How are viruses structured?
• Structures and Shapes
• Retroviruses

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What is a virus?

• An agent that causes disease in plants and
  animals
• Segments of nucleic acids (genetic material like
  DNA or RNA) contained in a protein coat

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What is a virus?

• Viruses are generally considered to be non-living
  because they DO NOT have all the characteristics
  of life.
• Viruses are different from living things in 3
  ways
• DO NOT grow
• CANNOT maintain homeostasis
• DO NOT metabolize

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What is a virus?

• Viruses are similar to living things in 2 ways
• 1. They contain nucleic acid (DNA or RNA)
• 2. They contain proteins (the capsid)

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Vocabulary

• Pathogen- agent that causes disease
• Host- an organism that shelters and nourishes a
  virus or another organism
• Capsid- the protein coat of a virus
• Envelope- surrounds the capsid and helps viruses
  enter cells

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Vocabulary cont

• Bacteriophage - a virus that
• attacks a bacteria
• (word parts - phage to eat)
• Prophage/Provirus - a viral DNA
• segment inserted into a bacterial cell

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Vocabulary Cont

• Retrovirus - a virus that replicates by first
  transcribing RNA into DNA (HIV)

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Vocabulary Cont

• Lysis - the breaking apart of the cell to release
  new viruses (word parts! lyse to burst)
• Viroid - a single strand of viral RNA that causes
  plant diseases (TMV)
• Prion - protein that infects animals

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Characteristics of a Virus

• When trying to find the cause of tobacco mosaic
  disease (disease that stunts the growth of
  tobacco plants) scientists discovered something
  other than bacteria was causing TMD
• Concluded it was smaller than a bacterium and
  named it virus after the Latin word meaning
  poison

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Characteristics of a Virus

• 1935, Wendell Stanley concluded that TMD was a
  chemical rather than an organism/cell
• Today we know that Stanley had discovered the
  first virus

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• Viruses have the following characteristics
• Smaller than prokaryotic cells (like bacteria)
• Not normally classified (debate over living vs.
  nonliving)
• Live and reproduce ONLY inside other living cells
• Cause diseases such as colds, influenza (flu),
  AIDS, smallpox, measles, chicken pox, rabies,
  mumps, and mononucleosis

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How are Viruses Structured?

• Viruses have an outer layer called a capsid that
  is made of proteins
• Inside the capsid is genetic material such as DNA
  or RNA (but it never contains both as the same
  time)

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How are viruses structured?

• Some viruses have an envelope outside of their
  capsid as well as proteins that stick out to aid
  in entering host cells (similar to marker or
  receptor proteins on cells)

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Structure and Shapes

• 5 basic shapes of a virus
• Helical
• Spherical
• Polyhedral
• Binal
• Filovirus

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Structures and Shapes

• Helical
• RNA or DNA is coiled in a long narrow capsid
• Ex. Tobacco Mosaic Virus

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Structures and Shapes

• Spherical
• Typically studded with receptors, may be
  enveloped
• Ex. Influenza Virus (Flu)

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Structures and Shapes

• Polyhedral
• Geometric in appearance
• Ex. Adenovirus (causes the common cold)

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Structures and Shapes

• Binal
• Polyhedral capsid
• Helical tail
• Ex. Bacteriophage

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Structures and Shapes

• Filovirus
• No distinct uniform shape
• Threadlike loops
• Ex. Ebola virus

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HIV a Retrovirus

• HIV- Human immunodeficiency virus
• Structure
• Spherical
• Contains RNA
• Retrovirus
• Exterior wall made of glycoprotein

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HIV Retrovirus

• Function
• causes AIDS (acquired immune deficiency syndrome)
• binds to human immune cells at specific receptor
  sites
• is a special type of virus called a retrovirus
• virus that gets its genetic information copied
  backward from RNA to DNA
• when a retrovirus infects a cell, it produces a
  DNA copy of its RNA
• retroviruses are responsible for some types of
  cancer in animals, including humans

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Human Diseases Caused by Viruses
Category Disease
Sexually transmitted disease AIDS (HIV), genital herpes
Childhood diseases Measles, mumps, chicken pox
Respiratory diseases Common cold, influenza (flu)
Skin diseases Warts, shingles
Digestive tract diseases Gastroenteritis
Nervous System diseases Polio, viral meningitis, rabies
Other diseases Smallpox, hepatitis, Avian Bird flu, Ebola, SARS, West Nile
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How Viruses Spread

• Viruses are transmitted from one host organism to
  another by many different vectors.
• transmit to pass along
• vector the substance or path used to pass the
  virus along

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• Viruses, like other pathogens, are commonly
  transmitted through body fluids, including the
  spittle in your sneezes and coughs, mucus
  produced by many parts of your body such as your
  nose and lungs, and even the ear wax in your
  ears. They can be transmitted through
  contaminated food and drinks as well. Some
  require contact with body fluids such as blood,
  semen, or vaginal secretions that you do not
  usually encounter.

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• SOME viral infections can be prevented through
  vaccines, such as the flu vaccine available each
  year and the HPV vaccine available from your
  doctor. A vaccine is often a weakened form of
  the virus injected to prevent infection.
  Children in the United States are also commonly
  vaccinated against measles, mumps, chicken pox,
  and polio. There are vaccines available for some
  forms of meningitis, rabies, smallpox, and some
  forms of hepatitis, but they are only given to
  people at risk of getting the diseases such as
  first responders, medical personnel, soldiers,
  and even some teachers.

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• Unfortunately, viruses mutate rapidly and
  vaccines lose their ability to be 100 effective
  in preventing disease. This is why we have a new
  flu vaccine every year. It takes over a year to
  manufacture flu vaccine, therefore scientists
  have to predict what will be most effective in
  the future. Sometimes they have excellent
  predictions and almost everyone who gets the
  vaccine stays well. Sometimes, they dont have
  excellent predictions and many people get sick.
  Its still important to get the vaccine because
  there is often more than one flu virus going
  around and protection against at least some of
  the virus is better than none at all.

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• Once we do get sick with a viral infection, we
  dont have many effective ways to cure the
  infection. We do have some antiviral medications
  which help prevent viruses from replicating as
  rapidly as they would without it, and interferons
  which mimic molecules naturally produced by your
  body in response to viral infections.
  Antibiotics DO NOT have any effect on viruses and
  should never be given or taken for an infection
  such as influenza (which is a respiratory
  illness, NOT a digestive system illness) or a
  cold.

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• Our inability to vaccinate against and to cure
  viral infections is why it is so important that
  you always cover your mouth when you sneeze or
  cough, dont share drinks or eat after someone
  else, wash your hands frequently, and even avoid
  sharing earbuds!