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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 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 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