MGY277H1 Lecture Notes - Lecture 3: Apoptosis, Treatment As Prevention, Immune System

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Unit 3 – Viruses
Introduction to Viruses
Spanish Influenza (1918-1920)
40-100 million death
Spread by the soldiers travelling around the world during WWI
Those who didn’t die from Spanish influenza often died from secondary
ammonia
Scientists first though it was caused by bacteria, but later found to be
caused by viruses (H1N1 isoform)
What we will learn about Viruses
1. History
2. Classification
3. Life cycle (of animal viruses)
4. Infection
Virus – A sub-microscopic agent that CANNOT multiply unless it invade a specific
host cell and utilizes it machinery (genetic and metabolic)
Sub-microscopic can’t be seen under light microscope
(10-1,000 times smaller than the cell they infect)
Non-cellular infectious entities capable of infecting every known type of cell
Able to redirect a cell’s metabolism to reproduce viral particle
Infection with a virus typically causes damage to the host cell
Viruses are the most numerous biological entities on earth and have
many different roles
oSalt & fresh water ecosystem (virus kills water bacteria  fresh water)
Viruses can be found INSIDE and OUTSIDE of the cell, but they are non-
functional/inactive outside the cell
1. Viruses = infectious particles (active or inactive) NOT (living or dead)
2. Viruses MUST always be cultivated in cells for study
The structure of Viruses
Rabies virus transmitted by infected saliva through bite or wound which then
cause brain inflammation
Furious (anxiety, crazy behaviour, jerking motion, fear of water)
Paralytic
Louis Pasteur developed the 1 st
vaccine for Rabies
Developed the vaccine using the dry spinal cord of infected rabbits
Didn’t know the agent causing rabies
Virus History
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1st discovered through the damage of tobacco crop and plant (mosaic virus)
Though to be a bacteria, but later found to be not during a filtering
experiment (Martinus Beijerinck, Dmitri Ivanovsky)
1st animal viruses identified by Fredrich Loeffler (food and mouth disease0
Complete Viral Particle = Virion
All viruses have a protein capsid that surround the nucleic acid in its core
Nucleic acid + capsid = nucleoocapsid
Naked Virus (Nucleo-capsid) Enveloped Virus
No envelope, spikes on
nucleocapsid
Envelope is a lipid bilayers,
spikes on envelope
No matrix protein Matrix protein (highly organized
enzymes and protein) between
envelope and nucleocapsid
Virus Capsid made up of identical protein subunit = Capsomers
Capsomers are determined by it symmetry and whether its enveloped
3 types of symmetry:
Helical hollow tubes with protein walls that surround a RNA strand like a
spiral staircase, can have complex shape and naked or enveloped (tobacco
mosaic virus, naked viruses)
Icosahedral contain 20 equilateral triangular face and 12 vertexes, takes
least energy to assemble (Herpes)
Complex Mixture of structure (Phage viruses can have an icosahedral
nucleocapsid head with long helical tail)
Viral envelopes are part HOST part VIRUS
Envelope carbohydrate and lipids com from the host
Envelope proteins (spike) are virally-encoded
Spikes may be used to identify viruses
2 types of influenza spikes
oHemagglutin help bind virion to host cell (18 types)
oNeuraminidase (enzyme) release mature virions in to the host cell
(11 types)
4 possible nucleic acid of viral genomes
1. Double stranded DNA virus (Herpes Simplex virus)
Mostly commonly found, genome can be linear or circular
2. Single stranded DNA viruses (HPV)
3. Double stranded RNA viruses (Rotavirus)
4. Single stranded RNA viruses (SARS)
More often seen then double stranded RNA
Animal virus replication
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