Virus and Prion Notes

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Virus and Prion Notes

• Ch. 18

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Bacteria and Viruses
Chapter 18
18.2 Viruses and Prions
Viruses

• A nonliving strand of genetic material within a
  protein coat

• No organelles to take in nutrients or use energy

• Cannot make proteins

• Cannot replicate on their own

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Viruses tiny non-cellular particles of genetic
material and protein. Controversy over whether
living or non-living.
Table Reasons for classifying non-living vs.
living
Non-Living Living
No cell respiration Reproduces within host cell
No growth or protein synthesis Has genetic material
No independent movement Larger viruses may infect smaller viruses
No basic cell parts/organelles Large numbers found in marine environment which is thought to be source of early single celled organisms.
No independent functions
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Figure 19-11 Viruses and Cells
Section 19-2
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Invasion Methods

• Flu Attack! How A Virus Invades Your Body NPR

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Bacteriophage Invasion

• Bacteriophage invades a bacterium

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Structure

• Contain a nucleic acid and protein
• HEAD region
• Capsid--protein coat with nucleic acid core
• TAIL region
• to attach to host

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Bacteria and Viruses
Chapter 18
18.2 Viruses and Prions
Viral Infection

• In order to replicate, a virus must enter a host
  cell.

• The virus attaches to the host cell using
  specific receptor site on the plasma membrane.
• 3D shape of the virus coat interlocks with the
  matching site on the host cell (lock and key)

• Many viruses cannot be transmitted between
  different species.

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• Named for
• Disease they cause
• Organs they infect
• Code Numbers differentiating organs they infect
• Bacteriophage means bacteria eater - viruses
  which attack bacteria

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Figure 19-9 Virus Structures
Section 19-2
Tobacco Mosaic Virus
T4 Bacteriophage
Influenza Virus
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Bacteria and Viruses
Chapter 18
Viral Replication in Prokaryotes occurs in
cytoplasm as DNA is not in a nucleus pgs. 528
529
Lytic Cycle

• The host cell makes many copies of the viral RNA
  or DNA.
• Lysis of host cell

Lysogenic Cycle

• Viral DNA inserts, or integrates into a
  chromosome in a host cell.

• Infected cell will have the viral genes
  permanently.
• Viral DNA can separate and enter lytic cycle

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Animated Lytic Cycle
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Animated Lysogenic Cycle
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Bacteria and Viruses
Chapter 18
18.2 Viruses and Prions
Bacteriophage

• A virus that infects bacteria

Other Viruses

• HIV/AIDS- spread through sexual contact
• Rabies- effects nervous system
• HPV- cancer causing virus

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Figure 19-10 Lytic and Lysogenic Infections
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Bacteria and Viruses
Chapter 18
18.2 Viruses and Prions
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Hepatitis DNA Virus
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Herpes Virus DNA Virus
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Rhinovirus RNA virus
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Polio Virus RNA Virus
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SARS Virus RNA Virus
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Viral Replication in Eukaryotes occurs in nucleus
of cell (not pictured in text)

• 1. DNA viral diseases (not listed in text as
  such) examples hepatitis, chicken pox, herpes,
  shingles
• Structure DNA inside protein coat virus
• Reproduction information follows normal
  pathway DNA to RNA to proteins in cell

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• 2. RNA viral diseases p. 526 cold, mumps,
  measles, polio, flu, AIDS, SARS, West Nile, most
  plant viruses
• a. Structure RNA wrapped in protein coat,
  surrounded by an envelope of glycoprotein spikes
  that bind with the membrane receptor proteins on
  the host cell
• b. Reproduction
• 1. protein surrounding RNA dissolves
• 2. RNA synthesis occurs strand produces
  either new viral RNA or protein for the viral
  coat and spikes
• 3. New virus assembles uses the cell membrane
  to make an envelope

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• Damage from virus depends upon
• Are cells lysed? (remember what lysis is?)
• What type of cell is damaged polio damages
  nerves which cannot regenerate
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• Plant Viruses most are RNA viruses
• virus must breach cuticle and cell wall so
  damaged plants are more susceptible
• typically rod shaped
• spreads through cytoplasmic connections between
  plant cell walls
• insects and gardening tools can spread to other
  plants

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• Emerging Viruses how do they come into being?
• Current Hypothesis for Development of First
  Viruses first viruses were fragments of cellular
  nucleic acid that could transfer to another cell.
  Protein coat later developed for
  protection/recognition. Viral genetic material
  is similar to cellular genetic material.
• Contributing Factors for current new virus
  development
• RNA viruses high mutation rate RNA
  replication isnt proofread so more mistakes.
  Mutated forms do not trigger previous immunity
• Existing viruses may spread to new host through
  mutation or new opportunity to infect a new host
  Ex Hanta Virus to humans from the bites,
  urine or droppings of infected mice or rats
• Existing virus in small populated area becomes
  widespread as new methods of transmission occur
  Ex HIV

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• Retrovirus has two copies of RNA instead of one
  and contains the enzyme reverse transcriptase
  Ex HIV pg. 530
• Reverse transcriptase synthesizes DNA from RNA.
  Complementary DNA strands are formed
• The double strand of DNA is then inserted into
  host DNA to form a provirus which is the animal
  version of a prophage
• Lysogenic-type cycle runs
• Occasionally provirus is transcribed into RNA,
  makes new viruses which infects other cells

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RetrovirusThe HIV virus
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HIV Retrovirus Life Cycle

• Life Cycle of HIV, a Retrovirus

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Prions proteinaceous infectious particle
(protein that can cause a disease)

• 1. Normally exist in cells not sure of function
• 2. Shape multi-folded piece of paper
• 3. Diseases these diseases belong to a group of
  diseases called TSEs or transmissible spongiform
  encephalopathy prions able to trigger abnormal
  folding of certain normal cellular proteins
  called prion proteins that are found in abundance
  in the brain
• a. Mad Cow Disease
• b. variant CJD variant Creutzfeldt-Jacob
  disease in humans
• c. Scrapie in sheep affects their central
  nervous system, usually fatal
• d. chronic wasting disease in deer and elk

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PrionsProtein particles
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• 4. Prion Infection
• a. Causes normal proteins to mutate - in brain
  cells, causes lysis of cells
• b. Spread when prions move to new material
  not sure how this happens but may occur when
• 1. Prion exists in brain or spinal cord of a
  cow.
• 2. When the cow is butchered, contamination of
  the beef occurs from nervous tissue.
• 3. Humans eat the contaminated beef
• 4. The prion enters the humans nervous system.