1. Ch 9 DNA Structure and Function

2. ENDURING UNDERSTANDING
Living systems store, retrieve, transmit, & respond to information essential to life’s processes.

3. ESSENTIAL QUESTIONS Is DNA the “essence of life”?
How and why does DNA replicate?
How is DNA a genetic code?

4. DNA - the book of YOU (TED ed - 5 min video)

5. 9.1 Identifying the Genetic Material
DNA stands for
deoxyribonucleic acid.
DNA is pretty unusual in that it is about the only common molecule capable of directing its own synthesis.

6. Identifying the genetic material
In 1928, Frederick Griffith - pneumonia bacteria and mice.
This was one of the first experiments that hinted that DNA was the genetic code material.
In 1944, Oswald Avery and his co-workers demonstrated that DNA is the material responsible for transformation.
In 1952, Alfred Hershey and Martha Chase
“Hershey-Chase Experiment”.
Showed that viral genes are made of DNA, not protein.

7. A=T and C=G
In 1949, Erwin Chargaff discovered that the same amount of Adenine & Thymine and Guanine & Cytosine were present in organisms
Lead to complimentary base pair knowledge
The amount of AT, CG combos varied between different organisms

8. 1950s, Franklin & Wilkens, did research bouncing x-rays off crystals of various substances
( x-ray crystallography), including DNA, then exposing photographic film to the x-rays.
Studied the scatter patterns made by the x-rays bouncing off the crystals of various substances
Unfortunately, Franklin died of cancer soon afterwards, or she might have been more famous.
Rosalind Franklin
Maurice Wilkens

9. X-ray crystallography

10. James Watson & Francis Crick saw Franklin’s photographs of DNA x-ray crystallography, & from her pictures, able to determine double spiral or double helix.
Based on Chargaff’s, and Franklin’s & Wilson’s data, and their knowledge of chemical bonding in 1953, Watson and Crick published a paper in which they proposed and described a hypothetical structure for DNA.
Double helix – two strands twisted around each other like a winding staircase.

11. * Each shared 1/3 of the Nobel Prize
The Nobel Prize in Physiology or Medicine 1962
"for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living material"
Francis Harry Compton Crick
James Dewey Watson
Maurice Hugh Frederick Wilkins
United Kingdom USA UK and New Zealand
b b b d d. 2004
* Each shared 1/3 of the Nobel Prize

12. Mini quiz
In 1928, the experiments of Griffith demonstrated transformation of
a. R bacteria into S bacteria.
b. S bacteria into R bacteria.
c. heat-killed S bacteria into R bacteria.
d. S bacteria into heat-killed R bacteria.

13. ______ 2. In 1952, Hershey and Chase used the bacteriophage T2 to determine that genetic material is made of which of the following?
a. protein c. DNA
b. RNA d. 35S

14. ______ 3. A microorganism that is virulent is
A. able to cause disease.
B. bacteriophage.
C. transformed.
D. harmless.

15. ______ 4. Avery’s experiments showed that
a. DNA is responsible for transformation.
b. proteins are responsible for transformation.
c. bacteriophages are responsible for transformation.
d. virulent bacteria are responsible for transformation.

16. 9.2 The DNA Molecule DNA = Deoxyribonucleic acid
“Deoxyribo” = refers to deoxyribose sugar
“Nucleic acid” = refers to nucleotides bonded together

17. Remember nucleotides? Nucleotides are the subunits that make up DNA.
Each nucleotide is made up of 3 parts:
phosphate group
five-carbon sugar molecule (deoxyribose sugar)
nitrogen-containing base (nitrogenous base)

18. Nitrogenous base may be any one of 4 different kinds:
Sugar & phosphate group are the same for each nucleotide in a molecule of DNA.
Nitrogenous base may be any one of 4 different kinds:
1. Adenine A
2. Guanine G
3. Thymine T
4. Cytosine C
Purines- 2 rings of C and N atoms
Pyrimidines- 1 ring of C and N atoms

19. Purines Pyrimidines
Nitrogenous bases
A pairs with T
C pairs with G

20. Sugar phosphate backbone = sides of a ladder.
Paired nitrogen bases = rungs of a ladder.
Nitrogen bases face each other.
Double helix is held together by weak hydrogen bonds between the pairs of bases.

21. Pairing Between Bases
Watson & Crick determined that purines & pyrimidines on opposite strand always pair
A with T
C with G
Pairs this way b/c of structure and size
Are base-pairing rules

22. Complimentary Base Pairs: the sequence of bases on one strand determines the sequence of bases on the other strand.
A 2 H -bonds w/ T
C 3 H- bonds w/ G
Hydrogen bonds between the base pairs keep the two strands of DNA together.

23. Mini quiz
Each nucleotide in a DNA molecule consists of a A. sulfur group, a five-carbon sugar molecule, and a nitrogen base. B. phosphate group, a six-carbon sugar molecule, and a nitrogen base. C. phosphate group, a five-carbon sugar molecule, and an oxygen base. D. phosphate group, a five-carbon sugar molecule, and a nitrogen base.

24. In 1953, Watson and Crick built a model of DNA with the configuration of a A. single helix. B. double helix. C. triple helix. D. circle.

25. Which of the following describes the base-pairing rules in DNA. A
Which of the following describes the base-pairing rules in DNA? A. Purines pair only with purines. B. Pyrimidines pair only with pyrimidines. C. Adenine pairs with guanine, and thymine pairs with cytosine. D. Adenine pairs with thymine, and cytosines pairs with guanine.

26. Which of the following researchers took key photographs of DNA. A
Which of the following researchers took key photographs of DNA? A. Watson B. Crick C. Franklin and Wilkins D. Chargaff

27. Hot Dog DNA – Science Friday – 4min

28. 9.3 DNA Replication
When the double helix structure was first discovered, scientists were very excited about the complimentary relationship between the sequence of nucleotides.
Within 5 years of the discovery of DNA structure, scientists had firm evidence that complimentary strands of the double helix do serve as templates for building new DNA.

30. p. 198 Figure 9
Step 1: Before DNA replication can begin, must unwind double helix structure
DNA helicases – are enzymes that open double helix by breaking the hydrogen bonds
Proteins then hold them apart
Areas where the double helix separates is called the replication fork

31. Step 1

32. p. 198 Figure 9
Step 2: DNA polymerase add complimentary nucleotides to each strand
- DNA polymerase is an enzyme
- as the DNA polymerase moves along, two new double helixes are formed

33. Step 2

34. p. 198 Figure 9
Step 3: Two DNA molecules form that are identical to the original DNA molecule
The process of DNA polymerase making complimentary base pairs will continue until all DNA has been copied and the DNA polymerase receives a signal to stop.
The new DNA has a new and an original strand.
The sequences in both of these DNA molecules are identical to each other and to the original DNA molecule.

35. Step 3

36. DNA replication - video – 2.5min

37. Checking for Errors Wow!
In the course of DNA replication, errors sometimes occur and the wrong nucleotide is added to the new strand.
DNA polymerase has a “proofreading” role.
Can add nucleotides to a growing strand only if the previous nucleotide is correctly paired to its complementary base.
Can backtrack, remove wrong base, and add correct base.
Reduces errors in DNA replication to about 1 error per 1 billion nucleotides!

38. The Rate of Replication Figure 10 p. 200
Replication does not begin at one end of the DNA molecule and end at the other.
Prokaryotes – circular DNA – has two replication forks that begin at a single point
Eukaryotes –each chromosome contains a single long strand of DNA
Length = challenge!
Each human chromosome is replicated in about 100 sections that are 100,000 nucleotides long, each section with its own starting point.
An entire human chromosome can be replicated in about 8 hours.

40. Mini Quiz B A C

41. Quiz C D A

42. Review Key Concepts p. 201 p. 203 Standardized test prep example
Use Haiku resources to see animations & videos