1. Complementary Base Pairing Showing hydrogen bonding
Fig. 16-8
Complementary Base Pairing
Showing hydrogen bonding
Adenine (A)
Thymine (T)
Figure 16.8 Base pairing in DNA
Guanine (G)
Cytosine (C)

2. Sugar-phosphate backbone “sides of the ladder”
Fig. 16-UN2 G C A T T A
Nitrogenous bases
“rungs of the ladder” G C
Sugar-phosphate backbone
“sides of the ladder” C G A T C G
Hydrogen bond T A

3. Strands of DNA – run opposite each other; this is called antiparallel.
Fig. 16-7a
5 end
Hydrogen bond
3 end
1 nm
3.4 nm
Figure 16.7 The double helix
3 end
0.34 nm
Strands of DNA – run opposite each other; this is called antiparallel.
5 end
(a) Key features of DNA structure

4. Sugar–phosphate backbone 5 end Sugar (deoxyribose) 3 end
Fig. 16-5
Sugar–phosphate backbone  end
Nitrogenous bases
Purines
Adenine
Guanine
PurAsGold
Pyrimidines
Cytosine
Thymine
Uracil
PyCUT
Carbon 1 – bonds to nitrogen base
Carbon 3 – bonds to next nucleotide
Carbon 5 – bonds to phosphate group
Thymine (T)
Adenine (A)
Figure 16.5 The structure of a DNA strand
Cytosine (C)
Phosphate
DNA nucleotide
Sugar (deoxyribose)  end
Guanine (G)

5. Purine + purine: too wide
Fig. 16-UN1
Purine + purine: too wide
Pyrimidine + pyrimidine: too narrow
Purine + pyrimidine: width consistent with X-ray data

6. At first, Watson and Crick thought the bases paired like with like (A with A, and so on), but such pairings did not result in a uniform width
Instead, pairing a purine with a pyrimidine resulted in a uniform width consistent with the X-ray
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7. Watson and Crick reasoned that the pairing was more specific, dictated by the base structures
They determined that adenine (A) paired only with thymine (T), and guanine (G) paired only with cytosine (C)
The Watson-Crick model explains Chargaff’s rules: in any organism the amount of A = T, and the amount of G = C
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8. Concept 16.2: Many proteins work together in DNA replication and repair
The relationship between structure and function is manifest in the double helix
Watson and Crick noted that the specific base pairing suggested a possible copying mechanism for genetic material
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9. DNA replication 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
Fig
DNA replication 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
Semiconservative
Figure 16.9 A model for DNA replication: the basic concept

10. The Basic Principle: Base Pairing to a Template Strand
Since the two strands of DNA are complementary, each strand acts as a template for building a new strand in replication
In DNA replication, the parent molecule unwinds, and two new daughter strands are built based on base-pairing rules
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11. Do you know how to Use this codon chart? Second mRNA base
Fig. 17-5
Second mRNA base
Do you know how to
Use this codon chart?
First mRNA base (5 end of codon)
Third mRNA base (3 end of codon)
Figure 17.5 The dictionary of the genetic code

12. Enzymes involved in DNA Replication & Transcription
Function
Helicase
“molecular zipper” – unwinds double helix; breaks hydrogen bonds that holds base pairs together
Primase
Creates an RNA primer so DNA polymerase will know where to start in order to manufacture a new DNA strand.
DNA polymerase
Using a parent DNA strand, adds free-floating nucleotides (A, T, G, & C’s) covalently to the new strand being constructed.
ligase
“molecular glue” – joins fragments of the New DNA strand together
RNA polymerase (used in transcription)
Uses one strand of DNA as a template to construct mRNA – adds free-floating nucleotide
Exonuclease
Removes RNA primers from the DNA strand after replication has occurred, so DNA polymerase can come in and fill in the gaps with DNA nucleotides to finish the process. Fixes mistakes on DNA molecule.
Also can fix mutations that occur during DNA replication.

14. Transcription & Translation refer to diagram drawn on board also watch animations: DNAi.org Khanacademy.org Crash Course (youtube)

15. DNA – A Historical Perspective
– Charles Darwin, British naturalist - famous voyage on HMS Beagle – published famous book on the Origin of Species which reveals the idea of Evolution by means of natural selection.
1858 – Alfred Wallace, – British biologist conducting field work in Malaysia. Sends a short essay to Darwin with similar theory of evolution.
1865 – Gregor Mendel, Austrian monk – “Father of Heredity”
1869 – Johann Miescher (Swiss biochemist) – isolates DNA from WBC
1928 – Frederick Griffith – British Bacteriologist – discovers transformational factor
1944 – Oswald Avery et al. - Canadian-born American physician – shows that the transformational factor was not a protein but DNA
1947 – Erwin Chargaff – Austrian biochemist – developed Chargaff’s ratios
1952 – Alfred Hershey & Martha Chase – provide conclusive evidence that DNA is the transformational factor
1952 – Rosalind Franklin & Maurice Wilkins – use x-ray diffraction to analyze DNA
1953 – James Watson & Francis Crick construct double helix model of DNA

16. Johannes Friedrich Miescher 1844-1895
In 1869, first to isolate a substance he called nuclein from the nuclei of leucocytes or WBC
Collected these from pus he obtained from bandages at nearby hospitals.
He found that nuclein contained phosphorus and nitrogen, but not sulfur

17. Frederick Griffith
What is the transformational factor??? Is it DNA or Protein???
Griffith’s research, working with two strains of a bacterium, one pathogenic and one harmless,
addresses this vital question
In 1941, Griffith was killed at work in his London laboratory as a result of an air raid in the London Blitz.

18. DNA – A Historical Perspective
Griffith and Transformation
1928 – British pathologist was researching
How certain types of bacteria produced pneumonia
He isolated 2 different strains: R which was harmless and S - virulent

19. Live S-strain kills mouse

20. Injection of Rough Colonies ( R) Results in Live Mice

21. Heat-killed Smooth colonies (S) Result in Live Mice

22. Heat-Killed S + Live R = Dead Mice

23. EXPERIMENT RESULTS Mixture of heat-killed S cells and living R cells
Fig. 16-2
Mixture of heat-killed S cells and living R cells
EXPERIMENT
Living S cells (control)
Living R cells (control)
Heat-killed S cells (control)
RESULTS
Figure 16.2 Can a genetic trait be transferred between different bacterial strains?
Mouse dies
Mouse healthy
Mouse healthy
Mouse dies
Living S cells

24. Oswald Avery and DNA (1944)
Working along with Colin Macleod & Maclyn McCarty
Repeated Griffith’s work with modifications
Which molecule in the heat-killed was the transformational factor?
The components of the Ground up S were isolated, each mixed with R and injected into mice

25. Avery et. al
1944
If the Heat-Killed S-strain’s DNA is destroyed with DNAase then R-strain can not be converted
to live S-strain. The gene to produce the capsule has been destroyed.

26. In 1952, Alfred Hershey and Martha Chase performed experiments showing that DNA is the genetic material of a phage known as T2
To determine the source of genetic material in the phage, they designed an experiment showing that only one of the two components of T2 (DNA or protein) enters an E. coli cell during infection
They concluded that the injected DNA of the phage provides the genetic information
                                                                                                                                                                                     Alfred Hershey and Martha Chase. 1953
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27. Phage head Tail sheath Tail fiber DNA 100 nm Bacterial cell Fig. 16-3
Figure 16.3 Viruses infecting a bacterial cell
DNA
100 nm
Bacterial
cell

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

29. (b) Franklin’s X-ray diffraction photograph of DNA
Fig. 16-6
Figure 16.6 Rosalind Franklin and her X-ray diffraction photo of DNA
(a) Rosalind Franklin
(b) Franklin’s X-ray diffraction photograph of DNA

31. Maurice Wilkins
Kings College London

32. Erwin Chargaff (1905-2002) and “Chargaff’s Rules”
The bases were not present in equal quantities
They varied from organism to organism.
No matter where DNA came from — yeast, people, or salmon — the number of adenine bases always equaled the number of thymine bases and the number of guanine always equaled the number of cytosine bases.
He published a review of his experiments in 1950, calling the ratios — which came to be known as Chargaff’s Rules

33. Chargaff’s rules state that in any species there is an equal number of A and T bases, and an equal number of G and C bases
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