BIOC20 - Virology Lecture Notes Comprehensive
Overview of Viruses - Virology - very detailed notes
2026
,BIOC20: Principles of Virology
Lecture 1 (Chapter 1)
The Nature of Viruses:
Basics:
● The Virion (fully intact infectious virus - has all the
components to infect) consists of:
○ A nucleic acid genome (RNA or DNA)
○ An enclosed protective protein coat
(capsid)
■ Every virus has a capsid - a shell
○ Some viruses contain a lipid envelope - outermost layer (outer-coat+ lipid bilayer taken
from the host cell, which also takes protein from the host)
● Capsid could be spherical or rod-like
Dependence on hosts:
● Viruses are dependent on host cells
● Viruses are obligate intracellular parasites (needs to be inside a cell, and is a parasite as it steals
resources from the hosts to survive)
○ Can only replicate within a living cell
● Viruses lack many essential functions, therefore cannot survive on their own
○ Synthesis of basic biological building blocks (unable to make the basic building blocks of
life)
■ i.e. nucleotides, amino acids, CHO‘s, lipids (they can‘t make it but have to steal
it from the host to survive)
○ Generation of useable chemical energy (ATP)
○ Protein synthesis machinery
■ i.e. ribosomes, tRNAs
○ Without these, a virus is just a package of genes!
Replication:
● Virus particles break down (disintegrate) and release their genomes inside the cell, (Uncoating)
before it can replicate inside the host. Important for the particle to uncoat, because the genome
inside is responsible for the transmission and infection of the virus.
○ Released from the protective protein shell
● Once uncoated, the genome can be used a template for
mRNA synthesis ⇒ protein production
○ using the cell resources as a virus factory!
● Viral proteins work together to replicate virus particle
○ Newly made structural proteins (viral) encapsidate the new genomes to form progeny
virions
● Q ⇒ How is this process in contrast to unicellular organisms, like bacteria?
, ○ A: Instead of disintegrating, bacteria divide and grow exponentially - must divide and
make the building blocks first
● Viral proteins work together to replicate virus particle
○ Newly made structural proteins (viral) encapsidate the new genomes to form progeny
virions
Shapes and Sizes:
● Viruses have variety of distinct morphologies, genome sizes, and particles sizes
○ Smallest viruses are 20 nanometers (nm) in diameter, coding as few as 2 proteins (200
nt!)
○ Largest can be 500nm in diameter, coding > 1200 proteins (1.2M nt!)
○ NB: 1 nanometer = 1 millionth (10^-6) of a millimeter!
Relative Sizes of Human Viruses:
Genomes:
● Genomes can be:
○ RNA or DNA (not both)
○ Single or double stranded
○ Circular or linear
● Question 1: What are two problems related to an RNA genome?
○ Answers:Must synthesize mRNA from RNA template
■ Can’t make an mRNA transcript from an RNA template, can only make it from a
DNA template!
○ Must find a way to replicate RNA genome
● Question 2: How do viruses solve these problems?
○ Answer: Most RNA viruses encode RNA-
dependent RNA polymerase
○ RNA polymerase is not the same as reverse
transcriptase
Why Study Viruses:
)
, ● Viruses are important disease-causing agents
● Viruses can infect all forms of life
○ Animals, plants, insects, even bacteria, algae, fungi!
○ Lots of vegetation shortages are due to viru
● Viruses are the most abundant life form on earth: Using the example of the earth‘s oceans and
bacterial viruses (bacteriophages):
○ Numbers: 10-fold excess of viruses compared to bacteria (for every 1 bacteria there are
10 viruses)
○ Mass: weight of ocean viruses = 1 million blue whales
○ Length: lined head-to-tail would reach 200 million light years! (refer to text box, pg 6)
● Viruses are the most abundant biological entities in the oceans
Why Study Viruses Con‟t:
4 examples of how studying viruses has led to numerous
discoveries in molecular and cell biology:
1. Studying gene expression in DNA viruses ⇒
identification of promoters for eukaryotic RNA
polymerase
2. Studying replication of bacteriophages & animal virus
DNA ⇒ helped us understand the enzymes involved in
cellular DNA replication
3. Studying viral mRNAs of DNA viruses ⇒ RNA splicing in eukaryotic cells
4. Studying cancer-producing viruses ⇒ led to the isolation of numerous cellular oncogenes and
the understanding that cancer is caused by their mutation or unregulated expression
a. Oncogenes induce cancer division
● The ongoing study of viruses will undoubtedly continue to shed light on many important aspects
of cell and molecular biology
A Brief history of Virology: The scientific study of viruses is very recent
● TMV - First Virus Discovered
● Viruses were first distinguished from other microorganisms by
filtration
● Tobacco Mosaic Virus (TMV) discovered independently by two
scientists, came up with the word virus:
○ Russian scientist Dimitri Ivanovski (1892)
○ Dutch scientist Martinus Beijerinck (1898)
Contagium vivum fluidum (first name for a virus)
○ Slimy, liquid, or poison
● Historical experiment to identify tobacco mosaic
disease (caused by a filterable infectious agent!)
was killing tobacco plants
Viruses are Filterable Agents
1. Grinded the diseased leaves and put it in on a
filter
)
Overview of Viruses - Virology - very detailed notes
2026
,BIOC20: Principles of Virology
Lecture 1 (Chapter 1)
The Nature of Viruses:
Basics:
● The Virion (fully intact infectious virus - has all the
components to infect) consists of:
○ A nucleic acid genome (RNA or DNA)
○ An enclosed protective protein coat
(capsid)
■ Every virus has a capsid - a shell
○ Some viruses contain a lipid envelope - outermost layer (outer-coat+ lipid bilayer taken
from the host cell, which also takes protein from the host)
● Capsid could be spherical or rod-like
Dependence on hosts:
● Viruses are dependent on host cells
● Viruses are obligate intracellular parasites (needs to be inside a cell, and is a parasite as it steals
resources from the hosts to survive)
○ Can only replicate within a living cell
● Viruses lack many essential functions, therefore cannot survive on their own
○ Synthesis of basic biological building blocks (unable to make the basic building blocks of
life)
■ i.e. nucleotides, amino acids, CHO‘s, lipids (they can‘t make it but have to steal
it from the host to survive)
○ Generation of useable chemical energy (ATP)
○ Protein synthesis machinery
■ i.e. ribosomes, tRNAs
○ Without these, a virus is just a package of genes!
Replication:
● Virus particles break down (disintegrate) and release their genomes inside the cell, (Uncoating)
before it can replicate inside the host. Important for the particle to uncoat, because the genome
inside is responsible for the transmission and infection of the virus.
○ Released from the protective protein shell
● Once uncoated, the genome can be used a template for
mRNA synthesis ⇒ protein production
○ using the cell resources as a virus factory!
● Viral proteins work together to replicate virus particle
○ Newly made structural proteins (viral) encapsidate the new genomes to form progeny
virions
● Q ⇒ How is this process in contrast to unicellular organisms, like bacteria?
, ○ A: Instead of disintegrating, bacteria divide and grow exponentially - must divide and
make the building blocks first
● Viral proteins work together to replicate virus particle
○ Newly made structural proteins (viral) encapsidate the new genomes to form progeny
virions
Shapes and Sizes:
● Viruses have variety of distinct morphologies, genome sizes, and particles sizes
○ Smallest viruses are 20 nanometers (nm) in diameter, coding as few as 2 proteins (200
nt!)
○ Largest can be 500nm in diameter, coding > 1200 proteins (1.2M nt!)
○ NB: 1 nanometer = 1 millionth (10^-6) of a millimeter!
Relative Sizes of Human Viruses:
Genomes:
● Genomes can be:
○ RNA or DNA (not both)
○ Single or double stranded
○ Circular or linear
● Question 1: What are two problems related to an RNA genome?
○ Answers:Must synthesize mRNA from RNA template
■ Can’t make an mRNA transcript from an RNA template, can only make it from a
DNA template!
○ Must find a way to replicate RNA genome
● Question 2: How do viruses solve these problems?
○ Answer: Most RNA viruses encode RNA-
dependent RNA polymerase
○ RNA polymerase is not the same as reverse
transcriptase
Why Study Viruses:
)
, ● Viruses are important disease-causing agents
● Viruses can infect all forms of life
○ Animals, plants, insects, even bacteria, algae, fungi!
○ Lots of vegetation shortages are due to viru
● Viruses are the most abundant life form on earth: Using the example of the earth‘s oceans and
bacterial viruses (bacteriophages):
○ Numbers: 10-fold excess of viruses compared to bacteria (for every 1 bacteria there are
10 viruses)
○ Mass: weight of ocean viruses = 1 million blue whales
○ Length: lined head-to-tail would reach 200 million light years! (refer to text box, pg 6)
● Viruses are the most abundant biological entities in the oceans
Why Study Viruses Con‟t:
4 examples of how studying viruses has led to numerous
discoveries in molecular and cell biology:
1. Studying gene expression in DNA viruses ⇒
identification of promoters for eukaryotic RNA
polymerase
2. Studying replication of bacteriophages & animal virus
DNA ⇒ helped us understand the enzymes involved in
cellular DNA replication
3. Studying viral mRNAs of DNA viruses ⇒ RNA splicing in eukaryotic cells
4. Studying cancer-producing viruses ⇒ led to the isolation of numerous cellular oncogenes and
the understanding that cancer is caused by their mutation or unregulated expression
a. Oncogenes induce cancer division
● The ongoing study of viruses will undoubtedly continue to shed light on many important aspects
of cell and molecular biology
A Brief history of Virology: The scientific study of viruses is very recent
● TMV - First Virus Discovered
● Viruses were first distinguished from other microorganisms by
filtration
● Tobacco Mosaic Virus (TMV) discovered independently by two
scientists, came up with the word virus:
○ Russian scientist Dimitri Ivanovski (1892)
○ Dutch scientist Martinus Beijerinck (1898)
Contagium vivum fluidum (first name for a virus)
○ Slimy, liquid, or poison
● Historical experiment to identify tobacco mosaic
disease (caused by a filterable infectious agent!)
was killing tobacco plants
Viruses are Filterable Agents
1. Grinded the diseased leaves and put it in on a
filter
)
