Viruses Flashcards
Why are viruses known as obligate parasites?
They need a host to reproduce/replicate
They can’t replicate by themselves
two types of immunity
active
passive
explain active immunity
body produces antibodies
explain passive immunity
body receives antibodies
Virus structure
Viruses are tiny, non-cellular structures.
° They have an outer layer of protein called a capsid.
° They contain either RNA or DNA but never both.
° They have no organelles of their own.
° Viruses are non-living structures as they are non-cellular, have no organelles and are unable to reproduce themselves.
Stages of replication
The steps of viral replication are:
1. Attachment
2. Entry
3. Synthesis
4. Assembly
5. Release
replication : attachment
- Viruses attach to a living host cell by means of receptor sites.
replication: entry
Viruses then make a hole in the host cell and push their own DNA or RNA into it.
replication: synthesis
The host DNA is inactivated, and the viral DNA/ RNA is used to make new viral nucleic acid/ protein.
replication: assembly
New viruses are made in the host cells.
replication: release
The host cell bursts to release new viruses
Human diseases:
- HIV
- Influenza
- Warts
- Polio
Animal diseases:
- Rabies
- Cowpox
- Foot and mouth disease
Plant diseases
- Tobacco mosaic disease
- Potato mosaic disease
- Tomato mosaic disease
viruses: living argument
contain nucleus acid
have protein cost
can replicate
viruses non living
non cellular - lack plasma membrane and organelles
One type of nucleus acid
Cant reproduce on its own -> obligate parasites
Not killed by antibiotics - a substance produced by micro organisms that kill other micro organisms
no means of nutrition
dont respire
Shapes of viruses
round
rod
complex
bacteriophage
a virus that infects bacteria
medical and economic impact - disadvantages of viruses
Human disease - cold , flu , cold sore, measles , mumps
Plant disease - tobacco mosaic disease
Animal disease - rabies, foot and mouth
medical and economic importance of viruses - benefits of viruses
Generic Engineering - transfer genes from one organism to another (vectors)
Control of infections (bacterial infections) may reduce infections by antibiotic resistant bacteria
Control and immunity of viruses
Viruses are controlled by the body’s general defence system (e.Q. skin, mucus, stomach acid and phagocytes) and the specific defence system (i.e. antibodies are produced to disable viruses).
Vaccine - immunity to many virus infections can be produced artificially by
vaccination or by injecting antibodies.
Antibiotics kill bacteria but do not affect viruses.**
**Interferons are a range of substances produced by virus-infected cells to protect healthy cells. They can be made artificially and can help to treat colds and other virus infections.
Antiviral drugs are used to treat virus infections. These drugs interfere with viruses without affecting the host
Viruses may be controlled by
the general body defences
production of antibodies
vaccination
drugs (partially)
During 2009 swine flu spread through the
population of many countries. Younger
people were more at risk of becoming ill
with swine flu than older people. Using
your knowledge of the immune system,
suggest a reason for this.
(2010 HL’Q6)
previous exposure: antibodies, active immunity, memory T cells
