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VIRUSES
A gallery of falsely coloured transmission electron micrograph images captures the presumed order of events when the HIV virus
buds from the surface of a T-lymphocyte white blood cell. The virus particles attack T-lymphocytes, stealing their genetic
machinery, thereby forcing them to produce more copies of the virus.
(National Geographic.com)
Definition of Virus


A _____________ particle made up of proteincovered ________________that can invade living
cells
The word comes from the Latin word ______
meaning a ___________________of plant or
animal origin
Picture of a Virus


Spreading
potentially lethal
pathogens,
______________
particles (brown)
invade cilia (blue) in
the airways of the
human lung.
Image by Karsten
Schneider/Science Photo
Library
Different Viruses:


The ____________ of
a virus gives it a
characteristic shape
All viruses have 2
parts:
________________an
d a protein covering
called a ________
Just How Big IS a Virus??
http://www.cellsalive.com/howbig.htm
Classifying Viruses




Difficult to classify because viruses are ____
________
They do NOT metabolize energy or perform
____________________
They must live as ___________ within the cells of a
host organism
They depend on their hosts for respiration, nutrition
and all other functions of life to enable them to
reproduce
Classifying Viruses




Viruses ‘____________’ the host cell by altering its
genetic make up
Viruses have characteristic shapes but all have 2
components: ______________(DNA or RNA) and a
protein covering called a _______
Viruses...
Example: Plant viruses infect plants and animal
viruses infect animal
Bacteriophage


________ are viruses
that only infect
__________
They are also known
as ________________
The Reproduction Cycle of Viruses


Are 2 ways a
virus can
___________,
depending on the
type of virus
The ________
Cycle OR
The _________
Cycle
Lytic Cycle
Step 1:
Virus _________
to the host cell
wall (ex. E. Coli)
by its _____
Lytic Cycle
Step 2:
Virus tail releases an
__________ dissolving
the cell wall which
creates an opening in
the cell
Lytic Cycle
Step 3:
The viral ______ then
takes over the host cell
and destroys the host
_______.
Lytic Cycle
Step 4:
Viral DNA then instructs
the cell to
________________ of
the viral DNA and
capsid
Lytic Cycle
Step 5:
The new viral
components are
assembled into 100 or
so _______ of the
original invader.
Lytic Cycle
Step 6:
Viruses produce lytic
enzyme that causes the
host cell to ______ (to
burst open)
Lytic Cycle
Step 7:
When the host cell
breaks apart, new
viruses are
__________ to infect
other cells
Just So You Know....



Bacteria are not defenceless against
_______________
Some bacteria have enzymes called _______
__________ that recognize foreign DNA
These restriction enzymes act like scissors and
‘___________’ the phage’s DNA making it useless!
Lysogenic Cycle
Step 1:
Virus enters a host but
doesn’t take over by
destroying its DNA.
Instead, it _______
with the host DNA.
(lysogeny)
Lysogenic Cycle
Step 2:
Cell _________ many
times with the newly
configured (combined)
DNA
Lysogenic Cycle
Step 3:
Virus can be copied
through many
generations and lies
________
Lysogenic Cycle
Step 4:
The virus is _________
by some environmental
stimulus.
Lysogenic Cycle
Step 5:
Once ________,
the viral DNA
instructs the host
cell to
manufacture new
viruses using the
____
__________
Types of Viruses
RNA VIRUSES
 Have RNA instead of DNA as their genetic material
 RNA never becomes part of the host DNA
 RNA acts like messenger RNA in the cell
 mRNA gets instructions to manufacture viruses and
bypass host cell DNA
 They are ______ viruses
 Example: most ______ viruses such as Tobacco Mosaic
Virus
Tobacco Mosaic Virus
Types of Viruses
Retroviruses
 Also contain RNA as genetic material vs. DNA
 When a virus infects a cell, it makes a copy of
_____________ from the viral RNA code
 Remember, _________ genetic transfer is from DNA to
RNA but these viruses ________ the direction of genetic
information transfer from normal to ‘_____________’
 i.e. – RNA to DNA (viral RNA copied to make the host
viral DNA)
 This reverse of direction gives rise to their name
______________
Type of Viruses
Retroviruses Continued...
 They are ____________ because there is no bursting of
the cell
 Example: ______ (human immunodeficiency virus)
which can cause AIDS (acquired immunodeficiency
syndrome)
 The virus enters a human white blood cell and makes
the cell make DNA from the viral RNA – the new DNA
becomes part of the hereditary apparatus of the
infected human cell
 The host cell does not burst BUT changes in ________,
____________, and ________
HIV
Structure of HIV
Purple (artificially dyed) virions on surface
of a salmon –coloured T cell.
Types of Viruses
Viral Diseases
 Viruses don't always use the lytic or lysogenic cycle
 They sometimes leave the host cell by pushing through the
_____________________
 This causes them to become __________ by the host cell’s
membrane
 Now the disguised ‘_____________’ virus spreads through
the body undetected
 Example: influenza, chicken pox/shingles, measles, mumps,
hepatitis (A, B ,C), warts, distemper, yellow fever,
mononucleosis, encephalitis and rabies
Chicken Pox Virus


Called __________
_______ virus (VZV)
Transmitted in
airborne _________
exhaled from an
infected person, the
virus causes a low
fever and a _____ of
fluid-filled blisters
Encephalitis




Encephalitis, or inflammation of the brain
tissue, is _______
When it strikes, it can be very serious, causing
_________________________,
_____________, ___________, and other
symptoms depending on the part of the brain
affected.
It is usually caused by one of several
________ infections, so it's sometimes
referred to as viral encephalitis.
Viral encephalitis may develop during or
after infection with any of several viral
illnesses including influenza, herpes simplex,
measles, mumps, rubella, rabies, chickenpox
and arbovirus infection including west nile
virus.
Virus Causes Coral Reef Bleaching?


A virus that kills _______ on coral reefs may be
causing widespread _________, according to
scientists at Plymouth Marine Laboratory (PML)
This bleaching is now reported in over ____
countries, across three major ________ and shows
that viruses play an important role in
_______________ dynamics.
Virus Causes Coral Reef Bleaching?


Mass bleaching events in 1998 and 2002 led to
destruction of up to ______ of corals in some areas
of the Great Barrier Reef and Indian Ocean and
_______________ is widely believed to be
responsible for the increased ___________ and
___________ of bleaching.
Until this discovery, the underlying cause and the
mechanisms involved were largely unknown.
Virus Causes Coral Reef Bleaching?



Shown that the symbiotic algae contain a latent
virus - it is only when they are stressed by
_____________ or ____________ that the virus
multiplies
Taken from:
http://www.pml.ac.uk/news_and_events/latest_news/virus_causes_coral_bleaching.asp
x?theme=textonly
This is still a ________ at this point