1. Bio 1010
Dr. Bonnie A. Bain 1

2. DNA Structure and Function
CHAPTER 10
DNA Structure and Function
Part 3
Viruses 2

3. Bring Scantron and #2 Pencil
Don't Forget: Exam 3
November 21
Bring Scantron and #2 Pencil 3

4. A change in a single nucleotide Frameshift Mutations:
Point Mutations:
A change in a single nucleotide
Frameshift Mutations:
An insertion or deletion of 1 or 2 nucleotides 4 4

5. Mutations are the ultimate source of diversity of life on our planet
Remember:
Mutations are the ultimate source of diversity of life on our planet 5 5

6. Figure 10.23 6

7. Figure 10.24
Viruses:
Genes in
Packages

8. Why talk about viruses here? Answer: Virus is “DNA in a Box”
A Virus consists of a protein coat (the box)
plus either a strand of DNA or RNA 8

9. Fig
Protein coat
DNA

10. Characteristics of Viruses 1. Has genes (DNA or RNA)
2. Reproduces by infecting other cells and hijacking their molecular machinery to make more viruses
3. Has a complex structure 10

11. Figure 10.24
Adenovirus
These cause respiratory infections in humans

12. Figure 10.25
Bacteriophage
200 nm
high or mm
Infect Bacteria

13. Fig c
Phage lambda
E. coli

14. Bacteriophage Reproduction
1. Inject their DNA into the “host” bacterium
2. The injected DNA forms a circle. The circle of DNA then hijacks the cell's machinery and makes lots more copies of itself as well as copies of the protein coat “parts”
3. New phages are assembled and then leave the bacterium (by lysing it, usually) 14

15. proteins are synthesized. Phage DNA is inserted into
Fig
Phage
Phage
attaches
to cell.
Phage DNA
Bacterial
chromosome (DNA)
Cell lyses,
releasing
phages.
Phage injects DNA
Many cell divisions
Occasionally a
prophage
may leave the bacterial
chromosome.
LYTIC CYCLE
LYSOGENIC
CYCLE
Phages assemble
Phage DNA
circularizes.
Lysogenic bacterium
reproduces normally,
replicating the prophage
at each cell division.
Prophage OR
New phage DNA and
proteins are synthesized.
Phage DNA is inserted into
the bacterial chromosome.

16. Bacteriophage Life Cycles
Lytic Cycle
After lots of viral copies made,
they escape the cell by lysing it
(breaking it open)
Lysogenic Cycle
Viral DNA replication occurs,
but no phage are produced
and the cell doesn't die

17. Figure 10.28
Influenza Virus
Causes the Flu

18. Figure 10.30a

19. Question: Are viruses alive??19

20. Characteristics of living organisms (page 4):
1. Organization and complexity
2. Regulation (physiology)
3. Growth and development
4. Utilize Energy
5. Respond to environment
6. Reproduce
7. Evolve (change over time) 20

21. How are viruses related to living organisms??21

22. Figure 14.26

23. Viruses originated from bacteria that became intracellular parasites
Origin of viruses
1. Regressive Theory:
Viruses originated from bacteria that became intracellular parasites
These became dependent upon a host
Then lost most of their genetic information 23

24. Viruses arose from host RNA or DNA that
Origin of Viruses
2. Run-away RNA:
Viruses arose from host RNA or DNA that
gained a self-replicative, but parasitic existence
and acquired the ability to replicate independently of their host 24

25. Viruses originated and evolved along with the most primitive molecules
Origin of Viruses
3. Co-evolution:
Viruses originated and evolved along with the most primitive molecules
(the first ones able to self-replicate)
Some molecules were packaged into membranes and eventually became cells
Others became packaged into protein coats and became virus particles that co-evolved with cells and parasitized them 25

26. Animal viruses: Many Viruses cause disease Adenovirus HIV Ebola Polio
Mumps
West Nile
Avian flu
SARS
Etc. 26

27. Plant Viruses: Many Viruses cause disease Tobacco Mosaic virus
infects lots of agricultural crops (tomato, squash, cantaloupe, etc.)
Papaya ringspot potyvirus (PRSV)
Kills papaya plants 27

28. Fig
RNA
Protein
Tobacco mosaic virus

29. Treatment of Viruses
Very hard to treat viral diseases
Antibiotics do NOT work on viral infections (only work on bacteria)

30. Treatment of Viruses
Many treatments that kill viruses will also kill the host
Antiviral Drugs:
Some focus on enzymes that the virus uses
High mutation rates in viruses
Best treatments are vaccinations
Your own immune system attacks viruses on contact

31. Figure 10.29
Mumps Virus
Life Cycle
(p. 191)

32. Virus Life Cycle (Enveloped RNA virus)
This type of virus has RNA covered with protein
First, the virus attaches to the cell with its protein spikes 32

33. Virus Life Cycle (Enveloped RNA virus) Then:
1. Viral envelope fuses with cell membrane;
allowing the viral RNA to enter the cytoplasm
2. Enzymes remove the protein covering around the viral RNA
3. Using the viral RNA as a template, a viral enzyme makes copies of the viral RNA 33

34. Figure 10.29
Mumps Virus
Life Cycle
(p. 191)

35. Virus Life Cycle (Enveloped RNA virus)
4. Two functions for the viral RNA copies:
a. Act as mRNA to make new viral proteins (using the host cell's ribosomes)
b. Act as templates for making more virus RNA 35

36. Virus Life Cycle (Enveloped RNA virus)
5. The newly made viral proteins assemble around the newly made copies of the virus RNA,
forming lots more new viruses
6. The new virus copies leave the cell 36

37. Figure 10.29
Mumps Virus
Life Cycle
(p. 191)

38. Lots of variations on the viral life cycle
Viruses can replicate in the nucleus or the cytoplasm of the host cell
Some viruses (Herpes simplex 1, 2; Polio virus) replicate inside nerve cells only 38

39. Lots of variations on the viral life cycle
Some are DNA viruses
Some are RNA viruses
Some reproduce like the Mumps virus
Others use Reverse Transcriptase (HIV virus) 39

40. Figure 10.30c

41. 1. Virus attaches to a white blood cell (T cell)
HIV virus
Causes AIDS
Life Cycle:
1. Virus attaches to a white blood cell (T cell)
and injects its RNA into the cell
2. The viral enzyme, Reverse Transcriptase, makes two copies of DNA using the RNA as a template 41

42. Figure 10.30a

43. HIV virus life cycle (con't)
3. The newly made viral DNA goes into the nucleus and inserts itself into the host cell's DNA
4. This is then transcribed and the mRNA is used to make new viral proteins (using the cell's ribosomes)
5. Newly formed viral particles leave the cell 43

44. 7. Viruses bud
from host cell
1. Attachment
6. Viral proteins
and RNA
assembled into
new virus
3. Viral RNA
to Viral DNA
2. Penetration
5. Viral proteins
and RNA synthesized
by host cell
4. Viral DNA
incorporated into host DNA

45. Figure 10.00a

46. Function: inhibits Reverse Transcriptase 2. Protease Inhibitors
Anti-HIV Drugs
1. AZT
Function: inhibits Reverse Transcriptase
2. Protease Inhibitors
Function: block the formation of the HIV viral proteins
This “drug cocktail” keeps the virus in check and extends people's lives, but it is NOT A CURE 46

47. Figure 10.1
How AZT
works

48. How Genes are Controlled (Gene Regulation) Don't Forget: Exam 3
Next Chapter: Chapter 11
How Genes are Controlled
(Gene Regulation)
Don't Forget: Exam 3
November 21
Bring Scantron and #2 Pencil 48