1. Cell Reproduction Unit Pictures The Code of Life

2. Cell Reproduction Unit Pictures
Topic 1
Experimental Evidence, Activity 1: What is the code of Life

3. Cell Reproduction Unit Pictures
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Freddy G (Griffith)
Disease-causing bacteria (smooth colonies)
Harmless bacteria (rough colonies)
Heat-killed, disease-causing bacteria (smooth colonies)
Control (no growth)
Dies of pneumonia
Lives
Live, disease-causing bacteria (smooth colonies)

4. Cell Reproduction Unit Pictures
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Ozzy A (Avery)

5. Obj 1
Ozzy A (Avery)

6. Figure 16.2b The Hershey-Chase experiment
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Cell Reproduction Unit Pictures

7. Activity A: Experimental Evidence Summary
Question?
Observation
Inference
Frederick Griffith
(R, S bacteria effects on mice)
What causes virulence in bacteria?
R strain bacteria transform into living S bacteria in the presence of dead S bacteria
Virulence was transferred from S to R bacteria
Oswald Avery (Griffith’s exp. with enzymes)
What is being transferred from S to R bacteria?
Dead S bacteria do not transfer virulence when DNA is digested with an enzyme
DNA is the molecule for information transfer (molecule of inheritance), not protein
Hershey and Chase
(bacteriophages)
What type of molecule is injected into bacteria (DNA or protein)
Radioactive DNA found inside of bacteria, radioactive protein found outside of bacteria

8. Cell Reproduction Unit Pictures DNA Structure and Replication
Topic 2
DNA Structure and Replication

9. Nucleic Acids DNA and RNA Monomer - nucleotide
Unit 1: Biochemistry and Digestion
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Nucleic Acids
DNA and RNA
Monomer - nucleotide
Five-carbon sugar (deoxyribose or ribose)
Phosphate group
Nitrogenous base
Adenine
Guanine
Cytosine
Thymine (DNA only)
Uracil (RNA only)

10. Cell Reproduction Unit Pictures
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DNA and RNA Nucleotides
Polymer – DNA or RNA
Monomers – Nucleotides
DNA – Cytosine, Thymine, Adenine, Guanine
RNA - Cytosine, Adenine, Uracil, Guanine
Single rings
Double rings

11. DNA Structure - Putting it all together…
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DNA Structure - Putting it all together…
Hershey-Chase and Avery– Convinced the world that DNA was the molecule of inheritance
Chargaff’s Rule – data collected showed that there are equal numbers of Adenine(A) to Thymine(T) and Cytosine(C) to Guanine (G)
Implied that the nucleotides are related in some way

12. Relative Proportions (%)of Bases in DNA
Cell Reproduction Unit Pictures
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Relative Proportions (%)of Bases in DNA
Organism A T G C
Human
Chicken
Grasshopper
Sea Urchin
Wheat
Yeast
E. coli
Chargaff saw that within a species, the amount of thymine always equaled the amount of adenine and cytosine equaled guanine

13. DNA Structure - Putting it all together…
Obj 4,5,6
DNA Structure - Putting it all together…
Hershey-Chase and Avery– Convinced the world that DNA was the molecule of inheritance
Most of the Chemical minds are now working on determining the structure of DNA
Chargaff’s Rule – data collected showed that there are equal numbers of Adenine(A) to Thymine(T) and Cytosine(C) to Guanine (G)
Implied that the nucleotides are related in some way
Rosalind Franklin – X-ray crystallographer
Produced ‘Photo 51’ image of DNA, showing consistent 2 nm diameter of DNA and parallel strands

14. Figure 16.4 Rosalind Franklin and her X-ray diffraction photo of DNA
Cell Reproduction Unit Pictures
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X-Ray Crystallography showed the double helix shape and showed that the helix was uniform in shape

15. Cell Reproduction Unit Pictures
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The only way it could be uniform in shape if is a purine always bonds with a pyrimidine

16. DNA Structure - Putting it all together…
Obj 4,5,6
DNA Structure - Putting it all together…
Hershey-Chase and Avery – Convinced the world that DNA was the molecule of inheritance
Most of the Chemical minds are now working on determining the structure of DNA
Chargaff’s Rule – data collected showed that there are equal numbers of Adenine(A) to Thymine(T) and Cytosine(C) to Guanine (G)
Implied that the nucleotides are related in some way
Rosalind Franklin – X-ray crystallographer
Produced ‘Photo 51’ image of DNA, showing consistent 2 nm diameter of DNA and parallel strands
James Watson, Francis Crick (and Maurice Wilkins)
Put it all together, make the first model of DNA
Win the Nobel Prize

17. Watson and Crick Model of DNA
Known:
Nucleotide structure and types (previous scientists)
Nucleotide abundance (Chargaff)
Double stranded, twisting (Franklin)
Nitrogenous bases pointing inwards (Franklin)
Inference (W and C)
Double Helix model
Base pairing
Sugar-phosphate backbone

18. Cell Reproduction Unit Pictures
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Base Pairing
Adenine and Thymine make 2 hydrogen bonds
Guanine and Cytosine make 3 hydrogen bonds
Watson and Crick literally made puzzle pieces to see how they fit together and discovered that adenine could make 2 hydrogen bonds with thymine and guanine could make 3 with cytosine
“Complementary bases”

19. Cell Reproduction Unit Pictures
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Sugar-phosphate Backbone
Covalent bonds between phosphate groups and sugars (Deoxyribose)
Forms via dehydration synthesis (polymerization)
Sugar-phosphate backbone
Nitrogenous bases stick into middle
The strands are antiparallel - they run in opposite directions
the side that ends in sugar is 3’ and the side that ends in phosphate is 5’

20. The Double Helix - structure
Cell Reproduction Unit Pictures
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The Double Helix - structure
Base pair = C-G and A-T
We say C and G are complementary and A and T are complementary
We say that human DNA contains over 6 billion base pairs - how many nucleotides?

21. Cell Reproduction Unit Pictures
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DNA strands are antiparallel
Important because..
Enzymes that interact with DNA only work in the 3’ to 5’ direction
Shape controls function!

22. Cell Reproduction Unit Pictures
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DNA Replication
Semiconservative model
Each strand of DNA is used as a template
Free nucleotides are connected according to base pairing rules
A to T
C to G
Results in two identical strands of DNA
Several enzymes make this work
The two parent strands become templates for assembly of a complementary strand from a supply of free nucleotides
The new strands are called daughter strands

23. Cell Reproduction Unit Pictures
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The process is called semi-conservative because half of the parental molecule is maintained in each daughter molecule

24. Closer Look at DNA Replication
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Closer Look at DNA Replication
Replication involves many enzymes!!!
DNA Helicase – unwinds the helix and “unzips” the base pairs
Forms the replication fork

25. Closer Look at DNA Replication
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DNA Polymerase – adds nucleotides to the template strand, creating a daughter strand
Several slightly different DNA polymerases work together to do this
DNA Polymerase only works in the 3’ to 5’direction
Creates a full Leading strand
Creates a segmented Lagging strand

26. Closer Look at DNA Replication
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DNA Ligase – Enzyme that closes the gaps in the lagging strand of DNA

27. THE END

28. Figure 16.8 Three alternative models of DNA replication
Cell Reproduction Unit Pictures

29. Cell Reproduction Unit Pictures
Figure The Meselson-Stahl experiment tested three models of DNA replication (Layer 4)
Cell Reproduction Unit Pictures