1. DNA
The Molecule of Life

2. Overview: Life’s Operating Instructions
1953
James Watson and Francis Crick
Structure of the molecule of inheritance
Deoxyribonucleic acid
Rosalind Franklin
Used X-ray crystalography to take the first picture of the molecule
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3. Figure
EXPERIMENT
Radioactive protein
Phage
Bacterial cell
Batch 1: Radioactive sulfur (35S)
DNA
In 1952, Alfred Hershey and Martha Chase performed experiments showing that DNA is the genetic material of a phage known as T2.
Radioactive DNA
Figure 16.4 Inquiry: Is protein or DNA the genetic material of phage T2?
Batch 2: Radioactive phosphorus (32P)

4. Batch 1: Radioactive sulfur (35S) DNA
Figure
EXPERIMENT
Empty protein shell
Radioactive protein
Phage
Bacterial cell
Batch 1: Radioactive sulfur (35S)
DNA
Phage DNA
Radioactive DNA
Figure 16.4 Inquiry: Is protein or DNA the genetic material of phage T2?
Batch 2: Radioactive phosphorus (32P)

5. Radioactivity (phage protein) in liquid Phage
Figure
EXPERIMENT
Empty protein shell
Radioactive protein
Radioactivity (phage protein) in liquid
Phage
Bacterial cell
Batch 1: Radioactive sulfur (35S)
DNA
Phage DNA
Centrifuge
Radioactive DNA
Pellet (bacterial cells and contents)
Figure 16.4 Inquiry: Is protein or DNA the genetic material of phage T2?
Batch 2: Radioactive phosphorus (32P)
Centrifuge
Radioactivity (phage DNA) in pellet
Pellet

6. Complimentary strands
Figure 16.7
Double helix
Nucleotide
Antiparallel
Complimentary strands
5 end C G
Hydrogen bond C G
3 end G C G C T A
3.4 nm T A G C G C C G A T
1 nm C G T A C G G C C G A T
Figure 16.7 The double helix. A T
3 end A T
0.34 nm
5 end T A
(a)
Key features of DNA structure
(b) Partial chemical structure
Space-filling model
(c)

7. Purine  purine: too wide
Figure 16.UN01
Purine  purine: too wide
Pyrimidine  pyrimidine: too narrow
Figure 16.UN01 In-text figure, p. 310
Purine  pyrimidine: width consistent with X-ray data

8. Two findings became known as Chargaff’s rules
Erwin Chargaff – measured the amount of each base (ATCG) in segments of DNA from different organisms
Two findings became known as Chargaff’s rules
The base composition of DNA varies between species
In any species the number of A and T bases are equal and the number of G and C bases are equal
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9. Sugar Sugar Adenine (A) Thymine (T) Sugar Sugar Guanine (G)
Figure 16.8
Sugar
Sugar
Adenine (A)
Thymine (T)
Figure 16.8 Base pairing in DNA.
Sugar
Sugar
Guanine (G)
Cytosine (C)

10. (a) Parent molecule A T C G T A A T G C Figure 16.9-1
Figure 16.9 A model for DNA replication: the basic concept.

11. (a) Parent molecule (b) Separation of strands A T A T C G C G T A T A
Figure A T A T C G C G T A T A A T A T G C G C
(a) Parent molecule
(b)
Separation of strands
Figure 16.9 A model for DNA replication: the basic concept.

12. (a) Parent molecule (b) Separation of strands (c)
Figure A T A T A T A T C G C G C G C G T A T A T A T A A T A T A T A T G C G C G C G C
(a) Parent molecule
(b)
Separation of strands
(c)
“Daughter” DNA molecules, each consisting of one parental strand and one new strand = semi-conservative
Figure 16.9 A model for DNA replication: the basic concept.

13. DNA Replication
Replication proceeds in both directions from the origins of replication.
replication fork - a Y-shaped region where new DNA strands are elongating
Helicases - enzymes that untwist the double helix at the replication forks
Single-strand binding proteins bind to and stabilize single-stranded DNA
Topoisomerase – enzyme that corrects “overwinding” ahead of replication forks by breaking, swiveling, and rejoining DNA strands
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14. Single-strand binding proteins
Figure 16.13
Primase 3
Topoisomerase
RNA primer 5 3 5 3
Helicase
Figure Some of the proteins involved in the initiation of DNA replication. 5
Single-strand binding proteins

15. Synthesizing a New DNA Strand
Enzymes called DNA polymerases catalyze the elongation of new DNA at a replication fork by adding to the 3’ end of an existing molecule.
Most DNA polymerases require an RNA primer (primase) and a DNA template strand to build from.
The rate of elongation is about 500 nucleotides per second in bacteria and 50 per second in human cells.
© 2011 Pearson Education, Inc.

16. Nucleoside triphosphate
Figure 16.14
New strand
Template strand 5 3 5 3
Sugar A T A T
Base
Phosphate C G C G G C G C
DNA polymerase OH 3 A T A
Figure Incorporation of a nucleotide into a DNA strand. T P OH P
P i P P C 3
Pyrophosphate C OH
Nucleoside triphosphate
2 P i 5 5
Nucleotides are added as nucleoside triphosphate (i.e. dATP).

17. Overall directions of replication
Figure 16.15
Overview
Leading strand
Lagging strand
Origin of replication
DNA polymerase can only add to the 3’ end (5  3).
Leading Strand
Lagging Strand
Okasaki Fragments
DNA ligase
Primer
Leading strand
Lagging strand
Origin of replication
Overall directions of replication 3 5 5
RNA primer 3 3
Sliding clamp
DNA pol III
Parental DNA 5
Figure Synthesis of the leading strand during DNA replication. 3 5 5 3 3 5

18. Overall directions of replication
Figure 16.15a
Overview
Leading strand
Lagging strand
Origin of replication
Primer
Leading strand
Lagging strand
Figure Synthesis of the leading strand during DNA replication.
Overall directions of replication

19. 3 5 3 Template strand 5 Figure 16.16b-1
Figure Synthesis of the lagging strand.

20. RNA primer for fragment 1
Figure 16.16b-2 3 5
Template strand 3 5 3
RNA primer for fragment 1 5 1 3 5
Figure Synthesis of the lagging strand.

21. RNA primer for fragment 1
Figure 16.16b-3 3 5
Template strand 3 5 3
RNA primer for fragment 1 5 1 3 5 3
Okazaki fragment 1 5 1 3 5
Figure Synthesis of the lagging strand.

22. RNA primer for fragment 1
Figure 16.16b-4 3 5
Template strand 3 5 3
RNA primer for fragment 1 5 1 3 5 3
Okazaki fragment 1 5 1
RNA primer for fragment 2 3 5 5 3 2
Okazaki fragment 2 1 3 5
Figure Synthesis of the lagging strand.

23. RNA primer for fragment 1
Figure 16.16b-5 3 5
Template strand 3 5 3
RNA primer for fragment 1 5 1 3 5 3
Okazaki fragment 1 5 1
RNA primer for fragment 2 3 5 5 3 2
Okazaki fragment 2 1 3 5
Figure Synthesis of the lagging strand. 5 3 2 1 3 5 5 3

24. RNA primer for fragment 1
Figure 16.16b-6 3 5
Template strand 3 5 3
RNA primer for fragment 1 5 1 3 5 3
Okazaki fragment 1 5 1
RNA primer for fragment 2 3 5 5 3 2
Okazaki fragment 2 1 3 5
Figure Synthesis of the lagging strand. 5 3 2 1 3 5 5 3 2 1 3 5
Overall direction of replication

25. Overall directions of replication
Figure 16.17
Overview
Leading strand
Origin of replication
Lagging strand
Leading strand
Lagging strand
Overall directions of replication
Leading strand 5
DNA pol III 3
Primer
Primase 3 5 3
Parental DNA
Figure A summary of bacterial DNA replication.
DNA pol III
Lagging strand 5
DNA pol I
DNA ligase 4 3 5 3 2 1 3 5

26. Overall directions of replication
Figure 16.17b
Overview
Origin of replication
Leading strand
Lagging strand
Leading strand
Lagging strand
Overall directions of replication
Leading strand
Primer
Figure A summary of bacterial DNA replication.
DNA pol III
Lagging strand 5
DNA pol I
DNA ligase 4 3 5 3 3 3 2 1 5

27. DNA Replication Complex
Figure 16.18
DNA pol III
Parental DNA
Leading strand 5 5 3 3 3 5 3 5
Connecting protein
Helicase
Lagging strand template 3 5
Figure A current model of the DNA replication complex.
DNA pol III
Lagging strand 3 5
DNA Replication Complex

28. Nucleotide Excision Repair
Figure 16.19 5 3
Hopefully:
DNA Polymerases edit the new strand as they move along the molecule = mismatch repair
If not: 
Nucleotide Excision Repair
Nucleases 3 5
Nuclease
Proofreading
Nucleotide Excision Repair 5 3 3 5
DNA polymerase 5 3
Figure Nucleotide excision repair of DNA damage. 3 5
DNA ligase 5 3 3 5