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Viruses
Are viruses living?
 No!
They are non-living but they depend on the
living.
Can you think of any viruses?
 H1N1
 West
Nile
 Seasonal Influenza (the flu)
 HIV
 Chicken Pox
 Rabies
 Ebola
Char. Of Life
VIRUS
CELL
Growth
No
Yes
Enzymes
Limited – uses host cell’s
enzymes to cause
reactions necessary for
themselves
Hundreds of
enzymes present
ATP
Cannot make ATP, uses
host cell’s ATP
Make own ATP
Mutations
Yes
Yes
Gene Make-up
DNA or RNA
DNA
Reproduction
Called replication, can only Called division by
occur within host cell
mitosis or fission,
occurs
independently
Structure
Nucleic acid core, protein
covering, some have
envelope
Cytoplasm, cell
membrane, etc..
Size comparison
Viruses and Bacteria
Viruses are
very small
particles and
measured in
nanometres
(1000nm =
1μm)
size demonstration
*VIRUS*
 Microscopic
particles capable of
reproducing only within living cells.
*2 main components*
 1.


 2.

Capsid
Capsid
Protein outer coat
Covers the nucleic
acid and protects it
Nucleic Acid Core
Genetic material
consisting of either
DNA or RNA
Genetic
material
 There
are specific
viruses which
infect animal, plant
or bacterial cells.
 Those
that infect
bacteria are called
bacteriophages.
*Bacteriophages Replicate in
2 ways…*
 Virulent
phages replicate actively and
cause lysis.
 Temperate
phages lie dormant for varying
periods of time, and can pass through
generations attached to a chromosome.
They cause lysogeneis.
Basic structure of a virus
helical
Some form
of
nucleic acid
(DNA or
RNA)
Enclosed in a
protein coat.
(capsid)
Bacteriophages
Viruses are specific to…
organism - ex. Hanta virus - carried
in mice (have no effect) but fatal to
humans
b) cell type - ex. human cold virus only
attacks cells lining the respiratory
tract.
ans
a)




Viruses are able to reproduce
ONLY inside living host cells.
They use the cell's genetic
machinery (ribosomes, enzymes) to
reproduce viral parts.
They are then assembled into many
new viruses which may rupture the
cell (destroying it), releasing these
viruses to infect more cells.
Viruses can be considered to be
intracellular parasites.
*Viruses may enter animal
cells in 3 possible ways:*
1.
2.
3.
Attachment and Injection
Endocytosis
Membrane fusion
1) Attachement and
Injection
Capsid
remains on
outside of host cell
Eg. Bacteriophage
Virus attaches to the bacterial
cell and injects its genetic
material into the cell through a
tiny syringe.
2) Endocytosis
 The
cell swallows up the virus through
phagocytosis.
 After
entering the cell, the virus sheds its
capsid (decapsidation), and the viral
genetic material takes over the cell.
3) Membrane Fusion
 Some
viruses have a membrane (from a previous
cell) that they fuse to the cell membrane and get
inside the cell.
 Once
inside, decapsidation occurs and the virus
takes over.
Viral Replication
(2 possible cycles):
Lytic and Lysogenic
1) Lytic Cycle
 the
replication process occurs in the cytoplasm of the
host cell




1. the virus’s genetic material enters the host cell
2. the cell replicates the viral DNA or RNA
3. the host cell makes new capsids and assembles new viral
particles
4. the host cell lyses (breaks open) and the new viruses
leave the cell
2) Lysogenic Cycle
Virus’s genetic material enters the host cell
nucleus and becomes part of the host cell’s
chromosome (provirus)
 In most cases the genes are not activated until
later
 Activation results in a continuation of the lytic
cycle

Chapter 2: Diversity: From Simple to Complex
Reproduction
UNIT 1
in Viruses
Section 2.1
Some Applications
Technology
Application or possible
application
Using a virus capsule to deliver a
drug
This method may be used to
deliver drugs to targeted cells in
the body, for example, to deliver
toxic chemotherapy to
cancerous tumour cells
Using a virus to insert a new copy
of a gene
This method may be used to
insert corrective genes into
individuals who suffer from a
genetic disorder
Using a virus to insert a gene
taken from one species into
another species
This method can be used to
create genetically modified
organisms.
It is widely used in the genetic
engineering of plants.
Video Clip – Flu Attack!
How a virus invades your
body (3:39)
 http://www.youtube.com/watch?v=Rpj0e
mEGShQ
Viral Replication
http://www.mcgrawhill.ca/school/schoolGraphics/biology2_1.mpg
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