Download Viruses - Mr Murphy`s Science Blog

Mr. E Murphy
Objectives
 What is a virus?
 Structure of a virus
 Virus replication
 Medical and economic importance of viruses
What is a virus?
Viruses are composed of a core of
nucleic acid surrounded by a
protein coat
 Outside living cells,
they are considered
non-living chemicals
 Inside a living cell, they
replicate using the host
cell
 Viruses have features of
both living and nonliving material
Smallpox virus
What is a virus?
Viruses can only multiply inside
living cells, therefore they are then
obligate parasites
 Viruses cause diseases
in humans, animals and
plants
 Different kinds of
viruses have different
shapes
 They can only be seen
with an electron
microscope
Structure of a virus
A virus is an infectious agent that
consists of nucleic acid (DNA or
RNA) enclosed in a protein coat
 They are not made of cells,
therefore don't have the cell
machinery for their own
metabolism
 Can only grow in living tissue
 Cannot be grown on agar
 Antibiotics do not work
against them, as there is no cell
machinery for the antibiotic to
damage
Virus Replication
Virus Replication
Most of our knowledge on viruses has
emerged from work carried out on
bacteriophages
1. Viruses attach to host cell
2. Either the whole virus or its nucleic
acid enters the cells cytoplasm
3. Viral nucleic acid takes over the
bacteria’s own DNA, making the
cell replicate the viral nucleic acids
and proteins
4. Nucleic acids and proteins are put
together to make new viruses
5. New viruses use enzymes to burst
out of the host cell
Medical and economic importance
of viruses
Disadvantages
 Human Diseases
 Viruses cause many diseases
such as measles, the common
cold and AIDS
• Plant diseases
 Plant viruses cause mosaic
disease in plants such as
tobacco, potato and corn
 Animal disease
 Foot and mouth, SARS and
rabies
Medical and economic importance
of viruses
Advantages
 Genetic engineering
 Control of infections