Viruses, viroids, and prions are infectious agents that are not considered living organisms. Viruses contain genetic material inside a protein capsule and reproduce by inserting their DNA or RNA into host cells. Viroids are small pieces of RNA that lack a protein shell and can still infect plants. Prions are infectious proteins that damage other proteins they contact. These three agents cause many diseases but viruses can also be used to deliver beneficial genes or drugs to cells through viral vectors.

1. Biological Kingdoms:
Viruses, Viroids, and Prions

2. Think. Pair. Share.
What is a virus?
Give an example of a specific virus.
Are viruses living or non-living?

3. Think. Pair. Share.
Which Domain do viruses belong to?
Which Kingdom do viruses belong to?

4. Viruses
• Influenza
• HIV
• Chicken pox
• H1N1
• Rabies
• Ebola
• T4 Bacteriophages

5. Viruses
A virus is a small infectious particles containing genetic
material (DNA or RNA) within a protein capsule (capsid).

6. Viruses
Viruses reproduce by inserting their genetic material
into host cells and "taking them over".
The general name given to a single virus particle that is
not infecting a cell is "virion".

7. Viruses
A virus is an obligate parasite; it requires a host
cell to reproduce.

8. Viruses
They are responsible for many diseases.
Epidemic: Large-scale disease outbreak in a region.
Pandemic: Multi-region or global disease outbreak.
AIDS

9. Viruses
There are many different ways viruses can be
transmitted:
Disease Transmission Method
rabies bites (saliva  blood)
HIV body fluid exchange
– excluding saliva
influenza, chicken pox, airborne/direct contact
common cold
measles, mumps direct contact

10. Viruses
They are non-living, thus they do not fall into any taxa.
Which properties of living things do they not have?

11. Differences Between Viruses and Cells
Life cycle:
How can
something
without life
have a "life"
cycle?
Genetic
material:
Viruses contain
RNA or DNA
Organelles: enclosed by
None. protein, not a
membrane.

12. Differences Between Viruses and Cells
Size:
Viruses are
much
smaller
than cells.
Metabolism:
Viruses do not
metabolize
(no
cytoplasm).

13. Viruses
Can be classified into orders/families/genera/species:
- size
- shape
- genetic material
- single-stranded or
double-stranded
DNA/RNA
- host cells
A bacteriophage (phage) is a virus that infects bacteria.

14. Virus Shapes - Cylindrical

15. Virus Shapes - Polyhedral

16. Virus Shapes - Spherical

17. Virus Shapes – Irregular (Bacterophage)
capsid (top half)
nucleic acid
tail (bottom half)
sheath
tail fibres
cell membrane
viral RNA/DNA injected
into host cell

18. Infectious Cycles
A virus infects a cell by inserting its nucleic acid into it.
The viral nucleic acid then enters 1 of 2 cycles:

19. Infectious Cycles
Lysogenic cycle: Host cell survives, but when it divides
the virus DNA/RNA is also duplicated.

20. Infectious Cycles
Lysogenic cycle: Host cell survives, but when it divides
the virus DNA/RNA is also duplicated.
Viral
DNA/RNA
Bacterial
DNA
A) Attachment
& Entry

21. Infectious Cycles
Lysogenic cycle: Host cell survives, but when it divides
the virus DNA/RNA is also duplicated.
Provirus
B) Integration – viral nucleic acid
becomes part of host nucleic acid

22. Infectious Cycles
Lysogenic cycle: Host cell survives, but when it divides
the virus DNA/RNA is also duplicated.
C) Multiplication of genome

23. Infectious Cycles
Lysogenic cycle: Host cell survives, but when it divides
the virus DNA/RNA is also duplicated.
D) Cell
division

24. A) Attachment bacterial B) Insertion
virus
DNA - Virus injects its
viral DNA nucleic acid
into host
bacterial host cell cell
E) Lysis &
Release
C) Replication
- The host’s
D) Assembly metabolism
- New viral particles replicates the viral
are assembled RNA/DNA

25. Infectious Cycles
The 2 cycles are
interchangeable
and a virus may
be in lysogeny
for many years.

26. Infectious Cycles
Sometimes newly formed viruses take sections host
DNA (and host genes) with them.
Transfer of genes using a virus is called transduction.

27. Vaccinations
Our immune systems can create a memory for
infections that we have previously fought-off.

28. Vaccinations
Previously encountered pathogens (like viruses) are
much more easily destroyed.

29. Vaccinations
Our immune systems can create a memory for
infections that we have previously fought-off.

30. Viruses - Benefits
How can a virus be used to benefit humans?

31. Viruses - Benefits
We can now craft viruses that contain beneficial genes
or drugs within their capsids (called viral vectors).

32. Viruses - Benefits
These vectors enter the target cells and deliver their
payload:
Vector Contents Application
Drugs Ex. Chemotherapy for
cancerous cells.
Copies of beneficial genes Gene therapy (replacement
or addition of new or better
genes).
Novel (new) genes Creation of GMOs
(genetically modified
organisms).

33. Viroids
A viroid is an infectious piece of RNA. It does not code
for anything and has no protective structure like a
capsid.

34. Viroids
These properties make them no less destructive to
simpler species.

35. Prions
A prion is a infectious protein. It has no outer structure,
but damages other proteins it comes into contact with.

36. Prions

37. Prions

38. Prions

39. Prions

40. Prions

41. Prions

42. Prions

43. Prions
Bovine spongiform encephalopathy (BSE, mad cow
disease) is caused by prions. Creutzfeldt-Jakob disease
(DJC) is caused by prions in humans.