The Genetics of Viruses

1
CHAPTER 19

• The Genetics of Viruses Bacteria

2
Lunchtime!!
T4 Bacteriophages
3
T4 Bacteriophage

• Bacteriophage virus that attacks bacteria
• Attacks Escherichia Coli bacteria
• Injects its DNA into the bacteriums DNA
• Virus takes over the bacteriums genetic
  mechanism
• Called an obligate intracellular parasite
• Obligate only exists in certain cases
• Intracellular Internal or inside cell
• Parasite lives off another organism

4
Viral Structure

• The smallest viruses are 20nm in diameter,
  smaller than a ribosome
• What does a ribosome do?
• What does that mean for its size relative to an
  animal cell?

5
Whos bigger?
6
Lets talk about viruses 1

• 1. HIV/AIDS
• In 2007, 33.2 million with HIV/AIDS
• 2.1 million fatalities from HIV
• 68 of infections are in Sub-Saharan Africa
• 2.5 million new infections in 2006
• Retrovirus

7
Viral Images
8
Lets talk about viruses 2

• 2. Influenza
• 7th leading cause of death worldwide, but not in
  the US
• Causes widespread pandemics every decade or so
• Fatality is more likely in the elderly infants
• Avian influenza in the 1990s was the last major
  pandemic

9
Lets talk about viruses 3

• 3. Ebola Hemorrhagic Virus
• Occasionally, Internal and external hemorrhage
  from orifices, such as the nose and mouth may
  also occur, as well as from incompletely healed
  injuries such as needle-puncture sites.
• Mortality rates are generally high, ranging from
  50 - 90
• Ebola is referred to as a slate wiper due to
  its remarkably high case fatality rate

10
Ebola outbreak in Congo
11
Are Viruses alive?

• They have DNA (or RNA)
• They are not able to reproduce on their own
• They infect other cells in order to perpetuate
  their life cycle
• Viruses can be crystallized, but no other cells
  can be crystallized
• May contain a membranous envelope

12
Viral Genomes

• Basically nucleic acid with a protein coat
• Some will have DNA (2-strands or 1-strand)
• Papillomavirus, Herpesvirus, Smallpox
• Parvovirus (1-strand)
• Others have RNA (2 or 1 strand again)
• HIV, Influenza Ebola
• Amount of genes also varies widely depending on
  the virus

13
Capsids Envelopes

• Capsid Protein shell enclosing the viral genome
• Rod-shaped, polyhedral, or more complicated (T4)
• Capsids are built from protein subunits called
  capsomeres
• Envelope Helps viruses infect their hosts
• Derived from the membranes of the host cell
• Host phospholipids membrane proteins

14
Viral Life Cycle Animation(s)

• 19_04SimpViralReproCycle

15
Simple Viral Reproductive Cycle
16
2 Types of Viral Life cycles

• Lytic
• Virulent cycle
• Results in death of host cell
• New phages are produced, host cell wall
  destroyed, and progeny (daughter viruses) are
  released to infect other cells
• Lysogenic
• Viral DNA is incorporated into host DNA
• This viral DNA is called prophage (provirus in
  euks.)
• Infection silently spreads to daughter cells

17
Lytic Cycle Animation

• 19_05PhageT4LyticCycle

18
Lytic Cycle
19
Lytic vs. Lysogenic Cycle

• 19_06LysogenicLyticCycle

20
Lytic vs. Lysogenic Cycle
21
HIV Life Cycle

• 19_08HIVReproCycle

22
(No Transcript)
23
Viroids Prions

• Viroids
• Just RNA
• Significantly smaller than viruses
• Infect plants
• Prions
• Proteins that are capable of infecting cells
• No DNA or RNA
• Causes degenerative brain diseases
• CJD (Creutzfeldt-Jacobs disease V1)
• Bovine Spongiform Encephalopathy (BSE)

24
Prions Alzheimer's

• Prions form into incorrect shape in CJD, but not
  so in Alzheimer
• Prions interact with plaques to allows the
  plaques to damage brain cells
• Amyloid-beta is the go between
• Mechanism of prion and amyloid-beta is unknown
• But sci. know there is an interaction, and this
  interaction Alzheimers
• Possible treatment avenue