1. DNA Replication

2. “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.”
Watson & Crick (1953)

3. Whiteboard
Draw a DNA nucleotide.
Hint:
circle
pentagon
rectangle

4. My image doesn’t have a rectangle as a base.
Oh well.

5. Whiteboard
Draw a second DNA nucleotide covalently connected to your previous drawing.

7. Whiteboard
Draw a two additional DNA nucleotides hydrogen bonded to your previous drawing.

9. Be Prepared to Answer this Question
How do the bonds found in DNA fit the mechanism for copying DNA?

10. How nucleotides are added in DNA replication
Watch and listen to the animation. Write down all key terms related to DNA replication.
How nucleotides are added in DNA replication

11. Helicase
breaks hydrogen bonds between bases, unzips and unwinds the helix

16. Whiteboard Draw a replication BUBBLE of DNA.
Do not erase when done...
Draw a replication BUBBLE of DNA.
Use an arrow to show where the origin of replication is located
Label the 5’ and 3’ end of each DNA strand
(you can decide which is which, just be sure it’s antiparallel)
Add two helicase enzymes, one at each FORK.
Usually drawn as ovals

17. AKA “topoisomerase”
2. Gyrase
Ahead of the replication fork, gyrase unwinds the DNA supercoil
Tension in coiling string demonstration

18. Whiteboard
Add a gyrase to each replication fork.

19. 3. Single Stranded Binding Proteins
Hold the DNA strands apart (keeps the separated strands apart and stabilize the unwound DNA).

20. Whiteboard
Add SSBP to each replication fork.

22. 4. PRIMASE AND PRIMERS

24. “Primer”

25. DANCE MOVE

26. Whiteboard
Create a table comparing DNA to RNA

27. 5. DNA Polymerase III
DNA polymerase III adds DNA nucleoside triphosphates to the RNA primer sequence in a 5’ to 3’ direction.
Huh?
What?

29. Where does energy for building DNA come from?
Ponder…..
Where does energy for building DNA come from?

32. Whiteboard Draw ATP, GTP, TTP, and CTP Hint: circles pentagon
rectangles of different size

33. Adding Bases
DNA polymerase III can only add nucleotides to 3’ end of a growing DNA strand
–needs a “starter” nucleotide to bond to
New strand only grows 5’ → 3’

34. On Your Notes Label the 3’ and 5’ end of the printed “parent” strand.
Draw in the new “daughter” strand working from 5’ to 3’.
Remember the strands are antiparallel!

35. Whiteboard
Draw this…
Label additional 5’ and 3’ ends 3’

36. Whiteboard
In a different color, add the new DNA strands that are being made and label their 3’ and 5’ ends. 3’

37. What is the “problem” or “limitation” with DNA polymerase III only being able to add to the 3’ end of a growing strand?
Whiteboard
Add in DNA polymerase III to show it building new DNA at the 3’ end of the new strands. 3’

39. Leading Strand
DNA polymerase III can synthesize a complementary strand on one side of the template in the 5’ to 3’ direction with no problem

40. DANCE MOVE

41. What about the other strand??

43. Lagging Strand
DNA polymerase III must work away from the replication fork.
Makes a short strand of DNA, called an Okazaki fragment.
As the bubble widens, it can make another short strand, and so on.

44. DANCE MOVE

45. 6. DNA Polymerase I
RNA primers are removed and replaced with DNA nucleotides by DNA Polymerase I.

46. DANCE MOVE

47. 7. DNA Ligase
Along the lagging strand the Okazaki fragments are joined by DNA Ligase to form a single DNA strand.

48. DANCE MOVE

49. DNA polymerase I 8. Proofreading –proofreads & corrects typos
–repairs mismatched bases
–removes abnormal bases
–reduces error rate from
1 in 10,000 to
1 in 100 million bases

50. DANCE MOVE

51. How nucleotides are added in DNA replication
Detailed Animation