1. Viruses Chapter 39

2. Objectives
Define viruses Consider whether they are living or non-living Describe the structure of a virus List the names of the virus shapes Describe how replication occurs in viruses Explain the medical importance of viruses to humans, plants and animals.

3. Viruses

5. Viruses
Viruses are tiny. They are much smaller (50 times) than a bacterium. An electron microscope is needed to see them. They are not made of cells and cannot reproduce on their own. Therefore they are not alive according to our rules.

6. Viruses are not living organisms?
Non-living
Possess genetic material either DNA or RNA
Are non-cellular
Possess a protein coat
Cannot reproduce by themselves
Can replicate (inside a living cell)
Only have one type of nucleic acid (living things have both DNA and RNA)

7. Viruses do not respire.
They cannot reproduce outside a host cell.
They are obligate parasites

8. Structure of Viruses
A virus consists of: A strand of genetic material either DNA or RNA. A protein shell called a capsid.

9. RNA or DNA? Viruses with RNA Viruses with DNA
Human immunodeficiency virus (HIV)
Influenza viruses
Rabies
Viruses with DNA
Warts
Chickenpox
mononucleosis

10. Shapes
Viruses can be:
Spherical
Rod shaped
Complex shaped

11. Bacteriophage
A bacteriophage or phage is a virus that infects bacteria
Bacteriophages are among the best studied viruses. T phage takes about
30 minutes to replicate.

12. The chart below shows the replication of a bacteriophage
The chart below shows the replication of a bacteriophage. This virus infects bacteria.
It takes about 30 minutes to complete its replication cycle.

14. Virus Replication Attachment
Proteins on the virus match up with the wall of the host cell
Entry
The virus forms a hole and the viral DNA is injected into the bacteria
Synthesis
The host DNA is switched off and the viral DNA takes over.
It makes virus parts.
Assembly
The virus parts are put together and new viruses are made.
Release
The host cell bursts and releases thousands of the viruses.
These move to other cells.

15. Disadvantages of Viruses
1. Diseases
Viruses cause many diseases in humans, animals and plants.
e.g. colds, measles, cold sores, mosaic virus in potato plants

16. Benefits of Viruses Genetic Engineering
Viruses can be used to transfer genes from one organism to another in genetic engineering. Such viruses are called vectors
e.g. human insulin gene transferred into E. coli
2. Control of infections
Bacteriophages may be used to control bacterial infections

17. Viruses can be beneficial…
Bacteriophages – attack & destroy bacteria
Baculovirus – ebola-like virus that attacks insects
Could use for pest control in crops
Cabbage loopers eat
cabbage crops
Virus can kill pests in days
(it’s really gross)
… and then there are those that are not so good….

18. Control & Immunity
Viruses are controlled by body’s general defence system e.g. skin
Immunity to many viral infections can be produced -by vaccinations or by injecting anti-biodies into the body.
Antibiotics kill bacteria and fungi but have no effect on viruses.

19. Interferon
Interferon is a range of substances produced by virus infected cells to protect healthy cells.
Interferon can be made artificially now and can be used to treat colds etc.

20. Viruses Enter Living Cells
Viruses enter bacterial cells by punching a hole in the cells wall and injecting its DNA

21. Mutating viruses
Viruses can mutate when they copy the genetic material
Copy something wrong
Mistake proves useful
More powerful virus (more infectious)
Viruses don’t mutate often, except…
Influenza & HIV

22. Retroviruses Retroviruses contain RNA instead of DNA
They have an enzyme that converts the Virus RNA to DNA
HIV is a Retrovirus

23. Plant Diseases Caused by Viruses
Potato Mosaic Virus

24. HIV Virus
AIDS: Acquired Immune Deficiency Syndrome is caused by the HIV virus
Effects: The virus damages the lymphocyte white blood cells making them unable to make antibnodies to fight against other diseases e.g. colds.
A person suffering from AIDS is unable to fight infections and may die from diseases e.g. cancer or pneumonia.
Spread: Spread through body fluids e.g. blood
Unprotected sex with an infected person or drug users sharing needles
Treatment: Drugs are given to slow down the progression of AIDS but there is no cure.

25. HIV Virus

26. How Is HIV Spread? Sexual contact Sharing contaminated needles
Blood transfusions
Breast feeding (mother to baby)
Mother to baby during pregnancy or birth

27. There are approx. 14,000 new cases of HIV worldwide every day
FACTS
In the US, there is better than a 1/1000 chance of contracting HIV during unprotected sex
A person can be contagious for more than 10 years before any sign of the disease is apparent
HIV becomes AIDS when the number of immune cells drops below a predetermined number
No one dies from HIV or AIDS; people die from secondary infections (ranging from the common cold to cancer)
More than 3 million people (size of Chicago) die each year
There are approx. 14,000 new cases of HIV worldwide every day

28. 2012 Q8 (Higher Level)

29. Solution to 2012 Q8

30. 2012 Section C Q14C

31. 2012 Section C Q14C Solutions

32. 2011 Paper Section C Question 15 Part c

33. 2011 Paper Section C Question 15 Part c Solutions