Review: Taxonomy

Who is the Father of Taxonomy?
– Carolus Linnaeus

Name the Levels of Classification?
– Kingdom, Phylum, Class, Order, Family,
Genus, Species

Which taxa are used in scientific names
of organisms?
– Genus and Species
Review: Taxonomy

How many kingdoms?
–6

Name the kingdoms
– Animalia, Plantae, Protista, Eubacteria,
Archaebacteria, Fungi
Viruses
Dead or alive?
What is a virus?

Viruses…
– are not cells
– do NOT grow
– do NOT carry out cellular processes
– Generate NO energy
– VERY SMALL!!! (20-400 nm)
• 1nm = 1 billionth of a meter!!
– Outside of living organisms they do
NOTHING!
Are viruses alive?
Yes and NO!
 Only 1 characteristic of life: reproduction
 A virus can only reproduce inside a
host cell!
 Process of reproduction = lytic cycle

Virus Categories

DNA viruses – stable, do not mutate
rapidly
– Single-stranded or double-stranded
– Smallpox, Hepatitis B

RNA viruses – mutate rapidly, unstable
– Single-stranded or double-stranded
– HIV, Rhinovirus

NEVER both!
Viral Structure
Icosahedral
(multiple triangular faces)
CAPSID: surrounds
the virus, made of
protein
Viral Structure
Helical
Viral Structure
Complex (ex. bacteriophage = attack bacteria)
Capsid
Nucleic Acid
(DNA or RNA)
Viral Structure
Enveloped
Quick Review!

What types of nucleic acids do viruses
possess?
– DNA or RNA

What is the size range of a virus?
– 20-400 nm

Which SINGLE characteristic of life is
common with that of a virus?
– Reproduction

Name some different viral structures
– Icosahedral, Helical, Complex, Enveloped
Viral specificity

Proteins located on the capsid make the
virus specific for receptor sites on the
host cell
Examples:
Hepatitis virus  infects the liver
Encephalitis virus infects the brain
Influenza virus  infects respiratory tract
Viral Specificity
Host Range: the limited number of host
species, tissues or cells that a virus or
other parasites can infect
 Some viruses have BROAD range

– Rabies virus infects many mammals and
humans!

Some viruses have NARROW ranges
– AIDS attacks white blood cells in humans
Viral Specificity
Animals
Plants
Humans
Rabies
Tobacco mosaic virus
Common cold
Avian flu
Tomato bushy stunt
Flu
Mad cow disease
Maize dwarf
German
measles/mumps
Cowpox
Sugar beat curly top
Chicken pox/small pox
Mononucleosis
Hepatitis
Herpes
AIDS
Viral replication

Viruses multiply like living organisms
BUT NOT on their own!

They require a host cell, using the cell‟s
machinery to copy it‟s nucleic acid and
make more of themselves!

They „hijack‟ the cell!!!
The LYTIC cycle
STEP 1: Attachment
Proteins on surface of virus act as keys
that fit into matching shapes on surface of
host cell
STEP 2: Entry
The virus injects its nucleic acid into the
cell, leaving the empty capsid outside the
cell
Some viruses enter the host cell intact
The LYTIC cycle
STEP 3: Replication
The viruses nucleic acid (DNA or RNA) is
copied and codes for making pieces of the
virus by host cell
STEP 4: Assembly
The pieces are put together to make a
virus
STEP 5: Lysis and Release
Host cell breaks open (lysis), as result
dies and NEWly made viruses are released
Before attachment
Attachment
Entry (Penetration and
uncoating)
Lysis and Release
Assembly
Replication
Draw the Lytic Cycle

Include ALL five steps
Review

Explain each step of the lytic cycle.
– Attachment, Entry, Replication, Assembly,
Lysis and Release

Is a virus living or non-living?
– Yes and No

What do viruses NEED, in order to
reproduce?
– Host cell
Review

What is meant by “Host Range”?
– The # of host species a virus can infect

What are the two virus categories?
– DNA viruses and RNA viruses

What are enveloped viruses?
– A virus with an extra layer of protection
Lysogenic Cycle
The alternative
 Similar to the lytic cycle

– Proteins on the surface of the virus bind
with proteins on the surface of the host cell
 this is specificity
– Virus attaches itself and injects its DNA
into cell
– Viral DNA attaches itself to host DNA,
becoming a new set of genes called a
prophage

When the host cell divides, this new
gene is replicated and passed to new
cells
– This causes NO harm to the cell, but may
alter its traits
NOW there are 2 possibilities
Prophage is a
permanent part of host
cell DNA
ex. Some flowers are
developed using viruses
to alter genetic code
External STIMULI causes
prophage to become active
(lytic cycle begins)
ex. Cancer works this way, they
are dormant and can be activated
by UV radiation or diet etc.

Virus undergoing LYTIC cycle
= a VIRULENT virus

Virus undergoing LYSOGENIC cycle
= a TEMPERATE virus
Defense Against Viruses

Viruses are EASY to destroy outside
living organisms
– They are WEAK!
– AIDS can be destroyed using bleach that
you can probably drink!

Once the virus is inside the cell, it is
powerful and substances that can kill it
will also kill the host cell (that is the
problem!)
Defense Against Viruses

Viruses can mutate and develop
resistance REALLY quickly
– LOTS of strains of the flu
Transmission

Vertical transmission: from mother to
baby
– Through body fluids or breast milk

Horizontal transmission: from person to
person (host to host)
– Droplet contact
– Fecal-oral transmission
– Sexual transmission
– Direct or indirect (vector) contact
Defense Against Viruses

Vaccination
– Effective prevention
– The shot is a live weakened (attenuated)
virus
– The formed antibodies bind the virus and
alert immune system
– Antibodies have „memory‟ and remember
the virus if it attacks
Our Natural Defense

White Blood Cells
– Engulf viruses in the blood and digest them

Interferons
– Proteins produced by immune system cells
when exposed to a virus
– Bind to membranes of neighbouring cells
and “interfere” with the ability of a virus to
attach and enter the cell
Questions

Explain why viruses are not living
organisms
– They only possess one characteristic of
life: Reproduction BUT they NEED a host
cell to carry out reproduction…can‟t do it
on their own

Draw the lytic and lysogenic cycle in
one