Download Chapter 25 Notes Viruses

Chapter 25 Notes
Viruses
Discovery of Viruses
 Scientists that helped in the discovery of
viruses
 Martinus beijerinck – studied the tobacco
plant are concluded that diseased plants
could infect the leaves of healthy plants
 Dr. Wendell Stanley – (1935) the first to
isolate the tobacco mosaic virus and show
that it could be crystallized
The Nature of Viruses
 Too small to be seen with a light microscope
 Viruses are much smaller then bacteria
 Viruses come in a variety of shapes
Composition and Structure
‫ ﻻ‬Viruses contain genetic material (DNA or
RNA) surrounded by a protein coat
‫ ﻻ‬Genetic material or nucleic acid is the core
and takes many forms (linear, circular,
double/single stranded)
‫ ﻻ‬Protein coat (CAPSID) – accounts for 95%
of a viruses weight
Composition and Structure
‫ ٭‬Most common structure is an icosahedron
which is a regular figure with 20 triangular
faces (looks like a knobby sphere)
‫ ٭‬Another common structure is a helix which
appears rod-shaped under the electron
microscope
Viruses and Life
‫ س‬When outside a host cell, a virus shows no
signs of life. To become active a virus needs a
host cell
‫ س‬Viruses are a lot like parasites except they do
not depend on their hosts for nourishment
because they do not grow
Reproduction
• Viruses reproduce by taking over a hosts cell’s machinery
• In bacteria, viruses inject nucleic acid, the
rest stays outside
• If a virus attack whole organisms they enter
intact once inside their genetic material is
released. They then use the organisms ATP
for energy and ribosomes to make new
proteins which are assembled with genetic
material to make new virus particles called
virons
Production
• The production of virons may cause cell death
• Viruses attack specific types of cells
• Ex – colds invade nose and throat epithelial cells
• Polio viruses attacks nerve cells in the brain ad
spinal cord
Term
• Virulence – The ability of a virus to
cause serious disease
RNA Viruses
Some viruses have RNA as it’s genetic
material instead of DNA
These viruses can still carry out
transcription and translation with the use
of special enzyme
Classification of Viruses
Presently viruses are classified
according to their size and shape
First classified as a DNA or RNA
viruses
Next subdivided on the basis of shape
Next subdivided on the basis of size
Bacteriophages
• Bacteriophages are viruses that attack bacteria
(bacteria eaters of phages)
• Structure of Bacteriophages – Nucleic acid core
and a protein coat just like all viruses. Six
structural types have been identified in their
protein coat. They are called T through T6. T is
the most studied bacteriophage as they infect the
E-coli bacteria. The T – even phages are virulent