Diversity of Living Things Part 2

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Diversity of Living Things Part 2

• Viruses

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Viruses

• A virus is classified as a non-cellular particle
  made up of protein-covered genetic material that
  can invade living cells.
• Many biologists do not classify viruses as
  belonging to any kingdom because they are not
  cells, do not metabolize energy or perform
  cellular respiration.
• Must live as parasites within cells of a host
• They enter a host and alter they host cells
  genetic make up.
• Have characteristic shapes
• They all have 2 things in common genetic
  material and a protein covering called a capsid.

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Viral Reproduction

• Viruses must invade a living host cell to
  reproduce
• 2 ways that viruses can reproduce depending on
  the type of virus The Lytic Cycle and the
  Lysogenic Cycle.

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Lytic Cycle

• Lytic Cycle always ends with the lysis (breaking
  open) of the host cell.
• The bacteriophage (type of virus that invades
  bacterial cells) attaches to the cell wall of the
  bacterium. Proteins in the tail of the virus
  code for specific virus-host infections.
• Bacteriophage tail releases an enzyme that
  dissolves the cell wall and the viral DNA is
  injected into the cell.
• The viral DNA takes over the cells activity and
  the host cells DNA is destroyed. The viral DNA
  instructs the cell to make copies of the DNA and
  capsid.
• Copies of viral DNA and capsid are made into new
  viruses, the cell breaks open and releases
  hundreds of new viruses.
• New viruses infect other cells.

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Lysogenic Cycle

• Lysogenic Cycle enter a host cell but do not
  take over the activity by destroying the host
  DNA, but combines with and becomes part of the
  host DNA in a way that does not interfere with
  the host cell activity.
• When the host copies its own DNA, it copies the
  viral DNA as well for many generations in
  lysogeny
• Changing conditions cause the phage to enter the
  lytic cycle.
• Bacteria are not defenseless against phage
  infections. Some bacteria have enzymes called
  restriction enzymes that can recognize foreign
  DNA, and cut up the DNA, making it useless.

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RNA Viruses

• Many viruses have RNA instead of DNA as their
  genetic material.
• Act as mRNA when in host and can manufacture
  viral proteins and bypass the host cells DNA.
• All are lytic.

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Retroviruses

• Contain RNA as well.
• When the virus infects the cell, it makes a copy
  of viral DNA from the viral RNA code. Normal
  copying is from DNA into RNA, so this process is
  backwards and thus they are called retroviruses.
• HIV (human immunodeficiency virus) that causes
  AIDS in humans is an example when the virus
  enters a human white blood cell and directs the
  cell to make DNA from the viral RNA. The new DNA
  becomes a part of the infected human cell. The
  host cell changes in shape, metabolism and growth
  and is lysogenic.

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Viral Diseases

• Have a lot of diversity and dont always
  replicate in either a lytic or lysogenic cycle.
• The human influenza virus does not lyse its host
  cell, but leaves by pushing out the cell
  membrane, coving itself in the cells membrane
  and is disguised as a human cell. The person
  will rapidly experience flu symptoms and become
  ill.
• Spread through coughing and sneezing, the
  incubation period is from one to four days,
  infectious people are contagious for about a
  week.
• Most viruses cause some type of disease in their
  host chicken pox/shingles, hepatitis A, B, and
  C, measles, warts, distemper, mumps, yellow
  fever, mononucleosis, rabies.
• Most plant viruses tend to be RNA viruses and can
  stunt plant grown and cause low crop yields. Can
  be spread by insects, farmers, gardeners using
  infected tools.

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Viroids

• Small, infectious pieces of RNA that are smaller
  than viruses and dont have a capsid.
• Plant pathogens that interfere with normal
  functioning of the host cells RNA.

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Prions

• Abnormally shaped infectious protein responsible
  for some brain diseases of mammals.
• Found in the brain and nervous tissue
• EG bovine spongiform encephalopathy (BSE) or
  mad cow disease