1. DNA and Replication

2. History of DNA

3. DNA DNA is often called the blueprint of life.
In simple terms, DNA contains the instructions for making proteins within the cell.
Why is DNA called the blueprint of life?

4. Why do we study DNA? We study DNA for many reasons, e.g.,
its central importance to all life on Earth,
medical benefits such as cures for diseases,
better food crops.
About better food crops, this area is controversial. There is a Dr. Charles Arntzen who is working on bioengineering foods with vaccines in them. People in poor countries could be immunized against diseases just by eating a banana, for instance.

5. Chromosomes and DNA Our genes are on our chromosomes.
Chromosomes are made up of a chemical called DNA.
{Ask students where the chromosomes are in this picture. Or ask them where the DNA is. Remind them that the mitochondria also have DNA.}

6. History of DNA
Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA
Proteins were composed of 20 different amino acids in long polypeptide chains

7. Transformation
Fred Griffith worked with virulent S and nonvirulent R strain Pneumoccocus bacteria
He found that R strain could become virulent when it took in DNA from heat-killed S strain
Study suggested that DNA was probably the genetic material

8. Griffith Experiment

9. History of DNA Chromosomes are made of both DNA and protein
Experiments on bacteriophage viruses by Hershey & Chase proved that DNA was the cell’s genetic material
Radioactive 32P was injected into bacteria!

10. Discovery of DNA Structure
Erwin Chargraff showed the amounts of the four bases on DNA ( A,T,C,G)
In a body or somatic cell:
A = 30.3%
T = 30.3%
G = 19.5%
C = 19.9%

11. Chargaff’s Rule Adenine must pair with Thymine
Guanine must pair with Cytosine
The bases form weak hydrogen bonds T A G C

12. DNA Structure
Rosalind Franklin took diffraction x-ray photographs of DNA crystals
In the 1950’s, Watson & Crick built the first model of DNA using Franklin’s x-rays

13. Watson and Crick

14. Rosalind Franklin

15. Pairs What have we learned about DNA so far?
What different experiments led to our current understanding of DNA?
What is Chargaff’s Rule?

16. DNA Structure

17. DNA Two strands coiled called a double helix
Sides made of a pentose sugar Deoxyribose bonded to phosphate (PO4) groups by phosphodiester bonds
Center made of nitrogen bases bonded together by weak hydrogen bonds

18. DNA Double Helix “Rungs of ladder” Nitrogenous Base (A,T,G or C)
“Legs of ladder”
Phosphate &
Sugar Backbone

19. Helix
Most DNA has a right-hand twist with 10 base pairs in a complete turn
Left twisted DNA is called Z-DNA or southpaw DNA
Hot spots occur where right and left twisted DNA meet producing mutations

20. DNA Stands for Deoxyribonucleic acid
Made up of subunits called nucleotides
Nucleotide made of:
1. Phosphate group
2. 5-carbon sugar
3. Nitrogenous base

21. DNA Nucleotide O O=P-O N CH2 O C1 C4 C3 C2 Phosphate Group
Nitrogenous base
(A, G, C, or T)
CH2 O C1 C4 C3 C2 5
Sugar
(deoxyribose)

22. Pentose Sugar Sugars are numbered clockwise 1’ to 5’ CH2 O C1 C4 C3 C2
(deoxyribose)

23. DNA P O 1 2 3 4 5 P O 1 2 3 4 5 G C T A

24. Pairs What three structures make up a nucleotide?
What are the four nitrogenous bases?
What is the base pairing rule?

25. Antiparallel Strands One strand of DNA goes from 5’ to 3’ (sugars)
The other strand is opposite in direction going 3’ to 5’ (sugars)

26. Nitrogenous Bases Double ring PURINES Adenine (A) Guanine (G)
Single ring PYRIMIDINES
Thymine (T)
Cytosine (C)
A or G
T or C

27. Base-Pairings Purines only pair with Pyrimidines
Three hydrogen bonds required to bond Guanine & Cytosine C G
3 H-bonds

28. Two hydrogen bonds are required to bond Adenine & Thymine

29. Question:
If there is 30% Adenine, how much Cytosine is present?

30. Answer: There would be 20% Cytosine Adenine (30%) = Thymine (30%)
Guanine (20%) = Cytosine (20%)
Therefore, 60% A-T and 40% C-G

31. RNA

32. RNA Differs from DNA DNA has a sugar deoxyribose
1. RNA has a sugar ribose
DNA has a sugar deoxyribose
2. RNA contains the base uracil (U)
DNA has thymine (T)
3. RNA molecule is single-stranded
DNA is double-stranded

33. Structure of RNA
Like DNA, RNA is a polymer of nucleotides. In an RNA nucleotide, the sugar ribose is attached to a phosphate molecule and to a base, either G, U, A, or C. Notice that in RNA, the base uracil replaces thymine as one of the pyrimidine bases. RNA is single-stranded, whereas DNA is double-stranded.

34. .
Three Types of RNA
Messenger RNA (mRNA) carries genetic information to the ribosomes
Ribosomal RNA (rRNA), along with protein, makes up the ribosomes
Transfer RNA (tRNA) transfers amino acids to the ribosomes where proteins are synthesized

35. DNA by the Numbers Each cell has about 2 m of DNA.
The average human has 75 trillion cells.
The average human has enough DNA to go from the earth to the sun more than 400 times.
DNA has a diameter of only m.
The earth is 150 billion m
or 93 million miles from
the sun.
If you unravel all the DNA in the chromosomes of one of your cells, it would stretch out 2 meters. If you did this to the DNA in all your cells, it would stretch from here to sun more than 400 hundred times!

36. DNA Model Make your own DNA model
A short research paper will accompany your model.
Include the the structures discussed in your notes:
Double helix, nucleotides, phosphate groups, sugars, and bases

37. DNA Song We love DNA made of nucleotides sugar, phosphate, and a base
bonded down one side.
Adenine and thymine
make a lovely pair
cytosine without guanine
would feel very bare.
D, D, DNA
different sets of genes
look inside the nucleus
for instructions to make proteins.
it’s the code of life
and the genetic makeup of
all you have in side.

38. DNA Song Assignment Requirements: Due by the next time we meet
Explain what makes up a DNA strand:
nucleotide
􀂾 sugar
􀂾 phosphate
􀂾 bases (nitrogenous)
Explain the base pairing concept:
􀂾 thymine pairing with adenine
􀂾 cytosine paring with guanine
Explain where DNA is found and that they are the instructions used to make proteins.
Explain that it is the genetic make-up of all organisms.
Explain how DNA is different than RNA

39. DNA Replication

40. Replication Facts DNA has to be copied before a cell divides
DNA is copied during the S or synthesis phase of interphase
New cells will need identical DNA strands

41. Synthesis Phase (S phase)
S phase during interphase of the cell cycle
Nucleus of eukaryotes
Mitosis
-prophase
-metaphase
-anaphase
-telophase G1 G2 S
phase
interphase
DNA replication takes
place in the S phase.

42. DNA Replication Begins at Origins of Replication
Two strands open forming Replication Forks (Y-shaped region)
New strands grow at the forks
Replication
Fork
Parental DNA Molecule 3’ 5’

43. DNA Replication
As the 2 DNA strands open at the origin, Replication Bubbles form
Eukaryotic chromosomes have MANY bubbles
Prokaryotes (bacteria) have a single bubble
Bubbles

44. Pairs What is the replication fork? When is DNA copied?
How is eukaryotic replication different than prokaryotic replication?

45. DNA Replication
Enzyme Helicase unwinds and separates the 2 DNA strands by breaking the weak hydrogen bonds
Single-Strand Binding Proteins attach and keep the 2 DNA strands separated and untwisted

46. DNA Replication
Enzyme Topoisomerase attaches to the 2 forks of the bubble to relieve stress on the DNA molecule as it separates
Enzyme
DNA
Enzyme

47. DNA Replication
Before new DNA strands can form, there must be RNA primers present to start the addition of new nucleotides
Primase is the enzyme that synthesizes the RNA Primer
DNA polymerase can then add the new nucleotides

49. Direction of Replication
DNA Replication
DNA polymerase can only add nucleotides to the 3’ end of the DNA
This causes the NEW strand to be built in a 5’ to 3’ direction
RNA
Primer
DNA Polymerase
Nucleotide 5’ 3’
Direction of Replication

50. Remember HOW the Carbons Are Numbered!
O=P-O
Phosphate
Group N
Nitrogenous base
(A, G, C, or T)
CH2 O C1 C4 C3 C2 5
Sugar
(deoxyribose)

51. Remember the Strands are AntiparallelO 1 2 3 4 5 P O 1 2 3 4 5 G C T A

52. Synthesis of the New DNA Strands
The Leading Strand is synthesized as a single strand from the point of origin toward the opening replication fork
RNA
Primer
DNA Polymerase
Nucleotides 3’ 5’

53. Synthesis of the New DNA Strands
The Lagging Strand is synthesized discontinuously against overall direction of replication
This strand is made in MANY short segments It is replicated from the replication fork toward the origin
RNA Primer
Leading Strand
DNA Polymerase 5’ 3’
Lagging Strand 5’ 3’

54. Lagging Strand Segments
Okazaki Fragments - series of short segments on the lagging strand
Must be joined together by an enzyme
Lagging Strand
RNA
Primer
DNA
Polymerase 3’ 5’
Okazaki Fragment

55. Joining of Okazaki Fragments
The enzyme Ligase joins the Okazaki fragments together to make one strand
Lagging Strand
Okazaki Fragment 2
DNA ligase
Okazaki Fragment 1 5’ 3’

56. Replication of Strands
Replication Fork
Point of Origin

57. Pairs
In what direction do nucleotides have to be added to the existing strand?
How is the leading strand different than the lagging strand?
List and describe the function of the enzymes involved with replication.

58. Proofreading New DNA
DNA polymerase initially makes about 1 in 10,000 base pairing errors
Enzymes proofread and correct these mistakes
The new error rate for DNA that has been proofread is 1 in 1 billion base pairing errors

59. Semiconservative Model of Replication
Idea presented by Watson & Crick
The two strands of the parental molecule separate, and each acts as a template for a new complementary strand
New DNA consists of 1 PARENTAL (original) and 1 NEW strand of DNA
DNA Template
New DNA
Parental DNA

60. DNA Damage & Repair
Chemicals & ultraviolet radiation damage the DNA in our body cells
Cells must continuously repair DAMAGED DNA
Excision repair occurs when any of over 50 repair enzymes remove damaged parts of DNA
DNA polymerase and DNA ligase replace and bond the new nucleotides together

61. Question: DNA 5’-CGTATG-3’
What would be the complementary DNA strand for the following DNA sequence?
DNA 5’-CGTATG-3’

62. Answer:
DNA 5’-GCGTATG-3’
DNA 3’-CGCATAC-5’

63. Replication Animation