1. Mrs. Stewart Biology I Honors
DNA
Structure
Mrs. Stewart
Biology I Honors

2. STANDARDS:
CLE Investigate how genetic information is encoded in nucleic acids.
CLE Describe the relationships among genes, chromosomes, proteins, and hereditary traits.

3. OBJECTIVES: (today, I will…)
Evaluate the structure of nucleic acids
Determine how genetic information is “coded” in nucleic acids
Create complementary DNA strands using Chargaff’s rule

4. Nucleic Acids Macromolecules containing : Carbon Hydrogen Oxygen
Nitrogen
Phosphorus
Function: Store and transmit genetic/hereditary information

5. Two types of Nucleic Acids
DNA
RNA

6. Deoxyribonucleic Acid
DNA Stands for:
Deoxyribonucleic Acid

7. DNA Structure
DNA is made up of two strands that are arranged into a twisted, ladder-like structure called a Double Helix.
A strand of DNA is made up of millions of tiny subunits called Nucleotides.
Each nucleotide consists of 3 parts:
Phosphate group
sugar
Nitrogenous base

8. Nucleotides
Phosphate
Nitrogenous
Base
Pentose
Sugar

9. DNA sugar The 5 carbon sugar for DNA is Deoxyribose
That is where the name (Deoxyribo)nucleic acid comes from

10. Nucleotides
The phosphate and sugar form the backbone of the DNA molecule, whereas the bases form the “rungs”.
There are four types of nitrogenous bases.

11. 4 different Nitrogen bases
Adenine T
Thymine C
Cytosine G
Guanine

12. Purines A
Adenine G
Guanine

13. Pyrimidines T
Thymine C
Cytosine

14. Chargaff’s rule
Erwin Chargaff observed that the percentage of adenine equals the percentage of thymine, and the percentage of cytosine equals the percentage of guanine.
Example: in one strand of DNA the following amounts may be found:
15% Adenine
15% Thymine
35% Cytosine
35% Guanine

15. Complementary base pairing:
Each base will only bond with one other specific base. (Chargaff’s rule)
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
Form a base pair.
Form a base pair.

16. Base Pairs: T
Thymine A
Adenine
Hydrogen bonds C
Cytosine G
Guanine

17. DNA Double Helix Made of 2 strands of nucleotides
These strands are joined together with the pairing of the Nitrogen bases
(A, T, C, G)
The bases are joined by Hydrogen bonds

18. Think – Pair - Share
Look at the picture and try to figure out what “antiparallel” means.
Did you notice that the strands of DNA run in “opposite directions”?

19. 5’ and 3’ ends of DNA
Refers to the orientation of the carbon atoms on the deoxyribose
Strands run in opposite directions
One strand is “upside down”

20. DNA Structure
Because of this complementary base pairing, the order of the bases in one strand determines the order of the bases in the other strand.

21. A C T G G A T C

22. Practice:
Complete the complementary DNA strand for the following sequence:
G T A A C T C C T
C A T A G A G G A
C T C C T A A A C
G A G G A T T T G
T A G A A T G C C
A T C T T A C G G

23. Bell Work Get one of each sheet on the front work desk
(2 worksheets and a strip of DNA)
Get plickers card

24. Mrs. Stewart Biology I Honors
DNA Replication
Mrs. Stewart
Biology I Honors

25. Face Partners
One of is you is Jim and the other is Dwight

26. STANDARDS:
CLE Investigate how genetic information is encoded in nucleic acids.
CLE Describe the relationships among genes, chromosomes, proteins, and hereditary traits.

27. OBJECTIVES: (today, I will…)
Evaluate the structure of DNA and the need for replication
Create complementary DNA strands to simulate replication

28. Central Dogma

29. Partners Think – Pair – Share
Why does DNA need to replicate itself?

30. Review: When does DNA copy itself?
Occurs during the S stage of interphase

31. DNA Replication
DNA makes an exact copy of itself

32. Animation of replication #1

33. Semi-conservative
Each strand of the double helix will serve as a template for the new strands that will form
End result is two complete DNA double helixes – each containing one strand from the original molecule and one newly made complementary strand

34. Jim – explain to Dwight what semi conservative means.

35. Helicase
Enzyme that “unzips” the DNA double helix by breaking the Hydrogen bonds between the bases to separate the strands in preparation for replication
Creates a “replication fork”

36. DNA Polymerase
Enzyme that builds the new strand of DNA using “free-floating” nucleotides in the nucleus

37. Dwight – Explain to Jim the role of Helicase in DNA replication

38. Jim – Explain to Dwight the role of DNA polymerase

39. 5’ to 3’ direction
DNA polymerase can only build DNA strands in the 5’ to 3’ direction.
Leading strand: forms continuously because it is already running in the 5’ to 3’ direction
Lagging strand: runs 3’ to 5’ so must form in short segments called Okazaki fragments that are joined together - this allows it to form in the 5’ to 3’ direction

40. Ligase
Enzyme responsible for joining the Okazaki fragments together

41. Dwight – explain the difference between the leading and lagging strands

42. Jim – explain to Dwight what Ligase does

43. Animation of replication #1

44. COMPLETE REPLICATION ACTIVITY AND QUESTIONS