Transcript viruses - Msleone.org

VIRUSES
Section 20.1
Key Players
 Dmitri


Ivanovski
Russian biologist in the 1890’s
Noticed tobacco plants were diseased but
only knew it was because of something in
the liquid secreted by the diseased plant.
Called the disease Tobacco Mosaic
Disease (1892)
 Martinus


Beijernick
Dutch biologist in the 1890’s
Suggested that tiny particles in the liquid
were causing the disease. Named the
particles “viruses” after the Latin word for
poison (1897)
Key Players Cont.
 Wendell


Stanley
American Biochemist in the 1930’s
Isolated crystals of the “Tobacco Mosaic
Virus”
 This
is important because living things DO NOT
CRYSTALLIZE which means viruses are not truly
LIVING THINGS.
What is a virus then?
A
virus is a nonliving particle made of
proteins, DNA, and sometimes fats.
 They
can only reproduce by infecting
other living cells.
Structure and Composition
 The
way viruses look varies greatly
 Most are so small they can only be seen
under an electron microscope
 Have
a protein coat that surrounds them
called a capsid.
 Simple viruses have only a few genes,
while more complex ones have thousands
Structure and Composition
 Proteins
on the capsid help them to enter
host cells.
 Most
viruses only can infect a specific kind
of cell

Example:
 Bacteriophage
– viruses that infect bacteria
What happens when a
virus infects a cell?
Lytic Infections
1.
2.
3.
4.
Virus enters bacteria cell
Virus copies itself
Too many copies cause the cell to burst
(lyse)
The extra copies go out an infect more
bacteria cells and the process happens
over and over and over and over and
over……etc.
Lysogenic Infection
•
1.
2.
3.
4.
Do not happen as quickly as lytic infections
Virus enters cells
Inserts a copy of the virus DNA into the
bacteria DNA
Cell unknowingly copies the virus DNA when
it copies its own DNA.
At some point the virus will take its DNA
back, create more viruses like in a lytic
infection and then the cell will burst and this
process will happen over and over and over
and over and over….etc.
A closer look at two
viruses
The common cold and HIV
The Common Cold
1.
2.
3.
A capsid enters a host cell usually in the
hosts nose.
The host inhales the capsid/cell deeper
into nasal cavity
The cold virus is a lytic infection so it
quickly copies itself and then when the
cell bursts, more copies of the virus go
out an infect other cells.
HIV
 Causes
1.
AIDS later in life
This is an infection called a retroviral
infection.
a)
2.
It is similar to a lysogenic infection
meaning it takes a long time for the virus
to infect the host.
The virus is transmitted through blood or
body fluid.
Characteristic
Virus
Cell
Structure
DNA or RNA in a
capsid
Cell membrane,
cytoplasm,
organelles
Reproduction
Only within a
host cell
Independent
cell division
Genetic Code
DNA or RNA
Growth &
Development
No
Obtain & Use Energy
No
Response to
Environment
No
Change Over Time
Yes
DNA
Yes
Yes
Yes
Yes