Transcript Viruses - Dominican

Viruses
• Extremely small (can
only be viewed using an
electron microscope)
• Non-cellular
pathogen
• Core of genetic
material – DNA or RNA
• Surrounded by wall of
protective protein
Capsid
Viruses – Living or Non - Living
• Viruses have none of the characteristics of
living things.
• They only respond when they make
contact with a suitable host
• All types of cells are attacked by viruses –
most viruses are specific to one cell type.
• Do not have ribosomes, mitochondria or
other cytoplasmic organelles cannot
carry out metabolisms on their own
• Must invade host cell to carry out rxn’s
Living
• Possess genetic
material DNA/RNA
• Possess protein coat
• Can replicate (inside
a living cell)
Non-Living
• Non cellular
• Cannot reproduce by
themselves
• Do not possess
ribosomes,
mitochondria etc
• Only have one type of
nucleic acid
A Bacteriophage is
a virus that infects
bacteria.
- Most complex
and best studied
viruses
Virus Replication
* As
viruses are not cells the term
replication is used instead of reproduction
 Attachment – virus attaches
to a suitable host cell
 Entry – the whole virus or its
nucleic acid enters the host cell
 Synthesis – the host
nucleic acid is inactivated.
The viral nucleic acid uses the
host’s organelles to produce
new viral nucleic acids
and protein
 Assembly – Viral nucleic
acid and proteins come
together forming new viruses
New virus DNA made using
bacterial organelles
 Release – host cell
bursts to release
between 100 and
100,000 new viruses
Bacterium
bursts
 Bursting of host cell is Many viruses
called lysis
released
Retroviruses
• Contain RNA instead of DNA
• Contain an enzyme that converts virus
RNA to DNA  DNA then makes new
copies of virus RNA and new viruses
inside the host cell.
• Example: HIV is a retrovirus
Some viruses do not destroy host DNA. Instead the viral
DNA joins with the host DNA and remains inactive
When the host DNA is copied, the viral DNA is also copied
and passed on to the daughter cells.
New host cells may behave normally or may produce new
chemicals due to the presence of the virus
Example : Diphtheria, scarlet fever and botulism
Economic importance of Viruses
• Crop damage e.g. mosaic disease of
potatoes, tomatoes and tobacco
• Livestock diseases e.g. foot and mouth,
rabies
• Work days lost due to viral infections e.g.
flu, colds
Medical Importance of Viruses
• Causes disease e.g. cold, cold sores, flu,
measels, rubella, mumps, chickenpox,
warts, hepatitis, viral meningitis,
HIV(AIDS)
• Some cancers are caused by viruses
• Vaccines – immunisation against viral
diseases
Beneficial uses of Viruses
• Act as vectors in genetic engineering
used to transfer genes from one organism
to another.
• Biological control : against pest rabbit
populations
Control and Immunity
• Controlled by the body’s general defence
system and specific defence system
• Immunity to certain viruses can be induced
artificially by vaccination
• Antibiotics kill bacteria but have no effect
on viruses
• Some antiviral drugs are available – they
interfere with the virus without affecting the
host. E.g. Acyclovir helps treat herpes
(cold sores)