Microbiology
October 30, 2009
A Lecture On Viruses In Three Acts
I. Ground Zero
a. Chapter 1: Doctrix Robson’s Checkered Past
i. Jeff infected her with a virus
1. She never knew his last name
b. Chapter 2: Viral replication
i. Viruses need a host cell to replicate
1. This is why they are only sort of considered alive and sort of considered not alive
ii. Step 1: Viruses attach to a host cell by interaction between specific protein on the host cell surface – this is allowed by viral protein
1. Bacteriophages: Capsid then stays on the outside of the host cell and inject their DNA directly into the host cell
a. Capsid – protein shell surrounding viral genome
2. For viruses that connect to eukaryotic cells: the virus is engulfed by the host cell; enzymes in our cells break down the capsid surrounding it’s genome, which in turn frees the genetic material of that virus
iii. Step 2: Viral genes expressed (i.e., genetic material of virus transcribed and translated into protein) by host cell and ribosomes, etc.
1. & Viral genetic material copied by host cell enzymes (DNA polymerase, etc.)
iv. Step 3: New viral genetic material (copied) packaged into new capsid proteins → new virus particles!
1. Some viruses: DNA (genetic material) of virus alone, in cell → new functional viruses
v. Step 4: Viruses are released form host cell
1. Eukaryotes: viruses often “bud” off of host cell ← not necessarily fatal to host cell but viral infection does keep cell from doing it’s job → can cause death (ex. HIV)
c. Chapter 3: Viral affinity for host cells
i. Viral interactions with host cell proteins is very specific, so specific – viruses can ONLY infect specific cells
1. Ex. Herpes simplex 1: cold sore virus → infects epithelial cells and neurons (only cells that have the right proteins on their surfaces for this virus to attach)
a. Go to the part of the spinal chord that feeds the lip epithelial cells – any time the immune system goes down a little bit (lack of sleep/run down) they will travel back up to the lip
II. The Curious Case of Dr. Wimmer
a. Chapter 1: Host cells, host species, and the potential for disease eradication
i. Eradication – destroy a disease so that it can never infect anyone again
1. Good candidates for eradication:
a. Viral disease that only infects humans and if you have a good reliable vaccine for the disease
2. Polio
a. 1988 – There was >125 endemic countries
b. 2006 – only 4 endemic countries
c. Eckhart Wimmer - Found genetic sequence online and synthesized an RNA strand with that sequence – creating his own polio virus
b. Chapter 2: Polio
i. Very small virus with an RNA genome
ii. Transmitted through contaminated water supplies
iii. Can only infect intestinal epithelial cells and neurons
1. In nature – can only infect these cells in humans
a. Because of this there is the potential to eradicate polio. (Eradicate – eliminate from planet earth)
iv. Causes Low level symptoms that don’t stay around for very long
v. If you get it when you’re older – causes paralysis to the motor neurons of the lower limbs
1. Franklin D. Roosevelt
vi. As long as the genetic sequence for polio exists – if anyone knows it – it will never be completely eradicated because it can be made very easily in a lab
c. Chapter 3: Viral Synthesis
III. Death Rides a Pied Horse
a. Chapter 1: The Pox!
i. Large virus with double stranded DNA genome
ii. Only infects human epithelial cells – and is VERY bad
1. Rapidly spreading blisters filled with a clear serum
2. In two weeks they burst leaving skin open to infection
3. Skin will never look normal again – normal scar tissue after a month or two
4. Mortality rate:
a. Experienced population – 30%
b. Naïve population – 90%
iii. Was a very affective vaccine for this
1. Problems:
a. Kills 1 in 1million people who get the vaccine
b. Even so the vaccine is still used all around the world because small pox is that terrible
i. These odds are better than having smallpox
iv. Wars would stop in their tracks so that people could come in and give soldiers and other people smallpox vaccines
b. Chapter 2: Hope springs eternal
c. Chapter 3: Victory
i. In late 1977 – declared smallpox to be dead
ii. The last known case was very light and was treated and killed in 1977
d. Chapter 4: Tragedy
i. People feared that smallpox could be used as a weapon
ii. A couple countries have a very small vile of smallpox just in case this is ever necessary
e. Chapter 5: The end?
i. The soviet viles of smallpox used to be in a freezer in Siberia under lock and key
ii. Now, they are nowhere to be found …
iii. No more experienced populations – 90% mortality rate if comes out again
