CHAPTER 19 The Genetics of Viruses & Bacteria

Lunchtime!! T4 Bacteriophages

T4 Bacteriophage  Bacteriophage – virus that attacks bacteria  Attacks Escherichia Coli bacteria  Injects its DNA into the bacterium’s DNA  Virus takes over the bacterium’s genetic mechanism  Called an obligate intracellular parasite  Obligate – only exists in certain cases  Intracellular – Internal or inside cell  Parasite – lives off another organism

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?

Who’s bigger?

Let’s 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

Viral Images

Let’s talk about viruses #2  2. Influenza  7 th 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 1990’s was the last major pandemic

Let’s 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

Ebola outbreak in Congo

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

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

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

Viral Life Cycle Animation(s)  19_04SimpViralReproCycle

Simple Viral Reproductive Cycle

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

Lytic Cycle Animation  19_05PhageT4LyticCycle

Lytic Cycle

Lytic vs. Lysogenic Cycle  19_06LysogenicLyticCycle

Lytic vs. Lysogenic Cycle

HIV Life Cycle  19_08HIVReproCycle

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)

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