1. DNA Structure and Function Crash Course:
Chapter 12

2. Chapter Mystery: UV Light
UV light can damage cells and kills nearly 10,000 Americans a year due to skin cancer. . .
BUT why is sunlight so dangerous? ?

3. What part of our cells does UV damage?

4. Early and Puzzling Clues
1860s: Frederich Miescher found DNA (deoxyribonucleic acid) in nuclei of cells. Easy to extract, but what is its function?
Early 1920s: Griffith transferred hereditary material from dead cells to live cells—used pneumonia bacteria

5. Griffith’s pneumonia experiments. . .
A Mice injected with live cells of harmless strain R do not die. Live R cells are in their blood. R
B Mice injected with live cells of killer strain S die. Live S cells are
in their blood. S
C Mice injected with heat-killed S cells do not die. No live S cells are in their blood.
D Mice injected with live R cells plus heat-killed S cells die. Live S cells are in their blood. R
Figure 13.2
Fred Griffith’s experiments, in which the hereditary material of harmful Streptococcus pneumoniae cells transformed cells of a harmless strain into killers.
Stepped Art
Fig. 13-2, p. 204

6. Avery and McCarty
1940: Avery and McCarty separated deadly S cells (from Griffith’s experiments) into lipid, protein, and nucleic acid components, then repeated Griffith’s experiments
Conclusion: DNA is the “transforming principle”

7. Study Question!
The process by which one strain of bacterium is apparently changed into another strain is called?
Transcription
Transformation
Duplication
Replication

8. Answer
Transformation !

9. The Hershey-Chase Experiments

10. Confirmation of DNA’s Function
1950s: Hershey and Chase experimented with bacteriophages (viruses that infect bacteria)
Protein parts of viruses, labeled with 35S, stayed outside the bacteria
DNA of viruses, labeled with 32P, entered the bacteria
Conclusion: DNA, not protein, is the material that stores hereditary information

11. So, where is the DNA?

12. Chromosome Structure
DNA is wound into chromosomes in the nucleus

13. How was DNA’s structure discovered?

14. Chargaff’s Rules
1950: Erwin Chargaff found that the amounts of thymine and adenine in DNA are the same, and the amounts of cytosine and guanine are the same.
The amount of A = T and G = C

15. Chargaff’s results:

16. The Discovery of DNA’s Structure
James Watson and Francis Crick’s discovery of DNA’s structure was based on almost fifty years of research by other scientists
They won the Nobel Prize with Maurice Wilkins in 1962 for the structure

17. Study Question
According to Chargaff’s rule base pairing, which of the following is true about DNA?
A=T and C=G
A=C and T=G
A=G and T=C
A=T=G=C

18. Answer!
a. A=T and C=G

19. Rosalind Franklin’s Image
Rosalind Franklin’s research in x-ray crystallography revealed the dimensions and shape of the DNA molecule: an alpha helix
Watson and Crick used the photo to build their model of DNA
Franklin died of cancer at age 37, possibly related to extensive exposure to x-rays

20. Parts of DNA
1. Phosphate 2. Deoxyribose Sugar 3. A Nucleic Acid (A, T, C or G) Also called a “nitrogenous base” Add all three of these parts to make one side of the DNA ladder called a nucleotide

21. Building the double helix
Now, each nucleotide can be bonded together in the middle to complete both sides of the ladder.
A bonds with T and C bonds with G

22. DNA’s Building Blocks Nucleotide
A nucleic acid monomer consisting of
a five-carbon sugar (deoxyribose)
a phosphate group
and one of four nitrogen-containing bases (nucleic acids)
DNA consists of four nucleotide building blocks
Two pyrimidines: thymine and cytosine
Two purines: adenine and guanine

23. STUDY Question!
What the three components DNA?

24. ANSWER!
Phosphate
Sugar
Nucleic Acid

25. 12.3 DNA Replication and Repair
When do cells need to copy their DNA?
A cell copies its DNA before mitosis or meiosis I
DNA repair mechanisms and proofreading correct most replication errors

26. Enzymes of DNA Replication
DNA helicase
Breaks hydrogen bonds between DNA strands
DNA polymerase
Joins free nucleotides into a new strand of DNA
DNA ligase
Joins DNA segments on discontinuous strand
DNA Replication:

27. A A DNA molecule is double-stranded.
The two strands of DNA stay zippered up together because they are complementary: their nucleotides match up according to base-pairing rules (G to C, T to A).
B As replication starts, the two strands of DNA are unwound. In
cells, the unwinding occurs simul- taneously at many sites along the length of each double helix.
C Each of the two parent strands serves
as a template for assembly of a new DNA strand from free nucleotides, according to base-pairing rules (G to C, T to A). Thus, the two new DNA strands are complementary
in sequence to the parental strands.
Figure 13.6
DNA replication. Each strand of a DNA double helix is copied; two double-stranded DNA molecules result.
D DNA ligase seals any gaps that remain between bases of the “new” DNA, so a continuous strand forms. The base sequence of each half-old, half-new DNA molecule is identical to that of the parent DNA molecule.
Stepped Art
Fig. 13-6, p. 208

28. Semiconservative Replication of DNA

29. Discontinuous Synthesis of DNA

30. A Each DNA strand has two ends: one with a 5’ carbon, and one with a 3’ carbon. DNA polymerase can add nucleotides only at the 3’ carbon. In other words, DNA synthesis proceeds only in the 5’ to 3’ direction.
Figure 13.8
Discontinuous synthesis of DNA.
Figure It Out: What do the yellow balls represent?
Answer: Phosphate groups
Fig. 13-8a, p. 209

31. Checking for Mistakes DNA repair mechanisms
DNA polymerases proofread DNA sequences during DNA replication and repair damaged DNA
When proofreading and repair mechanisms fail, an error becomes a mutation – a permanent change in the DNA sequence

32. The whole story of DNA Replication
. . .as told by N Sync: