MICI 2100 Lecture Notes - Lecture 12: Intracellular Parasite, Fetus, Serial Dilution
2 Nov 2018
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MICI 2100 – Lecture 12 October 16, 2018
Why Study Viruses?
• Viruses are all around us
• All living thing encounter billions of virus particles a day
• Infect all living things, plants, bacteria, insects, vertebrates, mammals
What Is a Virus?
Virus – (from Latin noun virus) means toxin or
poison (this is not always the case)
Viruses – are submicroscopic, obligate intracellular
parasites (meaning that viruses need to be
inside a cell to function)
• Virus particles are produced from the assembly
of pre-formed components (other agents grow
from an increase in the integrated sum of their
components and reproduce by division)
• Virus particles (virions) themselves do not grow or undergo division
• Viruses lack the genetic information that encodes apparatus necessary for:
a) Generation of metabolic energy
b) Protein synthesis
Once a virus has infected an cell, it has to produce its individuals proteins by cellular machinery. Virions
do not get bigger in size or undergo classical division. They have to infect a host cell for reproduction.
Viruses do not have their own metabolism and cannot synthesize proteins on their own, cellular
machinery is needed for these tasks.
What Does Virus Look Like?
Viruses come in different shapes and sizes. They can be
spherical, filamentous, helical (cylindrical) rods, etc.
Viruses Employ Different Strategies to Parasitize Host Cells
• As viruses are obligate molecular parasites, every
solution must reveal something about the host as well
as the virus
• Viruses are simple ‘Darwinian machines’ – survival of
the fittest
Is It Alive?
• Viruses challenge our definition of ‘LIFE’
o Certainly viruses multiply, but they do not ‘grow’
o Instead viruses harness cellular processes to direct genome replication and assembly of
progeny virions
One view:
Some researchers believe viruses are living inside a cell but non-living outside the cell.
Why Study Viruses?
• Viruses may:
o Cause disease
o Be beneficial
▪ Viruses contribute to host and
environmental homeostasis
▪ They keep our immune system alert
▪ They can be used as a flashlight to study regular host cellular processes (understand cellular
mechanisms better)
o Be benign
Viruses can be deleterious and cause disease but also can be beneficial or benign. Influenza virus would
cause respiratory tract disease. Ebola would cause a disease of internal bleeding and inflammation.
Some viruses might infect an bacteria that could’ve been pathogenic to us; in this case, it is beneficial.
• Study of viruses to:
o Aim for disease prevention
o Aim to conserve money and resources (Ex. In Canada, there were over 60,000 hospitalizations
due to influenza -> burden on hospital and staffs)
▪ Outbreaks and epidemics in humans and animals may cause great devastation in terms of
lives lost, increases in health care burden, and financial loss in agriculture
o Aim to increase our understanding of the fundamentals of host biology (simple cellular
replication, cellular genetics, etc)
Inside
Viruses Come in All Shapes and Sizes
Coliphage – is a type of bacteriophage
that infects bacteria, especially
Escherichia coli
Examples: Bacteriophage
lambda and Leviviridae
Most Viruses Are Smaller Than Bacteria
• Influenza virus is about 100nm.
• Herpesvirus is about 200 nm.
• Poliovirus is about 30 nm.
• Ribosome is about 20 nm.
Viruses Are Everywhere
• We eat and breathe billions of them
regularly
• We breathe 6L of air per minute
• Eat several kg of food per day
• Touch everything (doorknobs,
elevator buttons, etc.)
• We put our fingers in our eyes and
mouths
• Every milliliter of seawater has at
least 10 million virus particles
• We carry viral genomes as part of our own genetic material
• Viruses infect our pets, domestic food animals, wildlife, plants, insects
• Viral infections can cross species barriers, and do so constantly (zoonotic infections) -> Spillover
Swine flu is a crossover of a flu from a pig to a human.
Zoonotic infections (spillovers) – is the transfer of infection from animals to humans
Marine Viruses Affect the Global Carbon Cycle
• Microbes represent large majority of
biomass in the ocean
• Viruses are the most abundant entities in
global ecosystems
• Approximately 1030 viruses in the oceans
• Same amount of carbon as 75 million blue
whales
Prokaryotes have the largest biomass but viruses have the greatest abundance in the world’s oceans.
Document Summary
Mici 2100 lecture 12 october 16, 2018. Why study viruses: viruses are all around us, all living thing encounter billions of virus particles a day. Infect all living things, plants, bacteria, insects, vertebrates, mammals. Virus (from latin noun virus) means toxin or poison (this is not always the case) Once a virus has infected an cell, it has to produce its individuals proteins by cellular machinery. Virions do not get bigger in size or undergo classical division. They have to infect a host cell for reproduction. Viruses do not have their own metabolism and cannot synthesize proteins on their own, cellular machinery is needed for these tasks. They can be spherical, filamentous, helical (cylindrical) rods, etc. Viruses employ different strategies to parasitize host cells: as viruses are obligate molecular parasites, every solution must reveal something about the host as well as the virus, viruses are simple (cid:858)darwinian machines(cid:859) survival of the fittest.
