dna structure with photo 51

1. DNA StructureDNA Structure

2. How do cells “know” how to produce ATP?
How do cells “know” how to produce
other chemicals like enzymes?
How do cells “know” how to reproduce themselves?
What are genes?
How do genes work?
How do genes determine the characteristics of an organism?

3. History of DNA

4. In the 1900’s biologists were trying
to find these answers.
In order to understand genetics,
biologists had to figure out the
chemical structure of a gene.
(what are the parts & pieces?)

5. Friedrich Meischer – 1870’s
First to isolate DNA

6. Frederick Griffith - 1928
-Studied two types of bacteria (smooth/rough)
-cause of pneumonia (lung disease)

7. Type 2- (Rough looking)
•Rough looking (non-encapsulated)
•When injected harmless
Type 1- (smooth looking)
•Smooth looking (encapsulated)
•Disease causing
•Killed mice

8. Experiment # 1
Does the disease causing bacteria produce a poison?
Heat Killed
disease causing
bacteria (smooth)
Mouse LivedInjected into
the mouse
Summary: The mouse lived, this suggests that disease
causing bacteria (smooth) does not release a chemical poison.

9. Heat Killed
disease causing
(smooth)
Bacteria
+
live harmless
(rough) bacteria
Injected into
the mouse
Experiment # 2
Summary: By themselves neither should of made the mice sick,
however, many of the mice got pneumonia and died. The lungs
of the mice were filled with the disease causing bacteria.
DEAD

10. These experiments showed that one strain of bacteria
could be transformed into another type of bacteria.
Griffith’s Conclusion
Griffith hypothesized that when the live, harmless
bacteria and heat killed bacteria were mixed, some
factor was transferred from the heat killed cells
into the live harmless cells. This factor may contain
“information” that could transform the harmless
bacteria.
This was the first evidence that DNA stores and
transmits genetic information.

11. Oswald Avery - 1944
Oswald Avery led a group of scientists to further
investigate the work of Griffith. They wanted find out which
molecule in the heat killed bacteria was the most important
for transformation.

12. Summary:
Discovered that DNA stores and transmits the
genetic information from one generation of
organisms to the next generation.
(DNA)

13. STRUCTURE OF DNASTRUCTURE OF DNA
MonomerMonomer

Nucleotide (3 parts)Nucleotide (3 parts)
PhosphatePhosphate
Deoxyribose sugarDeoxyribose sugar
Nitrogen baseNitrogen base

Adenine (A)Adenine (A)

Thymine (T)Thymine (T)

Guanine (G)Guanine (G)

Cytosine (C)Cytosine (C)

14. Four bases...Four bases...
Purine basesPurine bases
Adenine andAdenine and
guanineguanine
Two carbon ringsTwo carbon rings
Pyrimidine basesPyrimidine bases
Thymine andThymine and
cytosinecytosine
A single carbonA single carbon
ringring

15. DNA chainsDNA chains
Nucleotides areNucleotides are
joined withjoined with
phosphodiester bond.phosphodiester bond.
What is the name ofWhat is the name of
the chemicalthe chemical
reaction that joinsreaction that joins
these monomers?these monomers?

16. Edwin Chargaff - 1947Edwin Chargaff - 1947
Studied DNA in various species.Studied DNA in various species.
Found that nitrogen-containing bases areFound that nitrogen-containing bases are
proportionate within each species.proportionate within each species.
The proportions hold true across species.The proportions hold true across species.
Came up with rules for complementaryCame up with rules for complementary
base-pairing.base-pairing.

17. Chargaff’s RulesChargaff’s Rules
Adenine and Thymine are found inAdenine and Thymine are found in
proportionate amounts.proportionate amounts.
%A = %T%A = %T
Cytosine and Guanine are found inCytosine and Guanine are found in
proportionate amounts.proportionate amounts.
%C = %G%C = %G

18. Rosalind Franklin
X-Ray Crystallographer
aka: X-ray diffraction

19. How Diffraction Works: Schematic
http://mrsec.wisc.edu/edetc/modules/xray/X-raystm.pdf
NaCl

20. Solving the Structure of DNASolving the Structure of DNA
Photo 51 AnalysisPhoto 51 Analysis
Photo 51- The x-ray diffraction image
that allowed Watson and Crick to solve
the structure of DNA
www.pbs.org/wgbh/nova/photo51

21. Solving the Structure of DNASolving the Structure of DNA
Photo 51- The x-ray diffraction image
that allowed Watson and Crick to solve
the structure of DNA
Photo 51 AnalysisPhoto 51 Analysis
 ““X” patternX” pattern
characteristic of helixcharacteristic of helix
www.pbs.org/wgbh/nova/photo51

22. Solving the Structure of DNASolving the Structure of DNA
Photo 51- The x-ray diffraction image
that allowed Watson and Crick to solve
the structure of DNA
Photo 51 AnalysisPhoto 51 Analysis

““X” patternX” pattern
characteristic of helixcharacteristic of helix

Diamond shapesDiamond shapes
indicate long, extendedindicate long, extended
moleculesmolecules
www.pbs.org/wgbh/nova/photo51

23. Solving the Structure of DNASolving the Structure of DNA
Photo 51- The x-ray diffraction image
that allowed Watson and Crick to solve
the structure of DNA
Photo 51 AnalysisPhoto 51 Analysis

““X” patternX” pattern
characteristic of helixcharacteristic of helix

Diamond shapesDiamond shapes
indicate long, extendedindicate long, extended
moleculesmolecules

Smear spacing revealsSmear spacing reveals
distance betweendistance between
repeating structuresrepeating structures
www.pbs.org/wgbh/nova/photo51

24. Solving the Structure of DNASolving the Structure of DNA
Photo 51- The x-ray diffraction image
that allowed Watson and Crick to solve
the structure of DNA
Photo 51 AnalysisPhoto 51 Analysis

““X” patternX” pattern
characteristic of helixcharacteristic of helix

Diamond shapesDiamond shapes
indicate long, extendedindicate long, extended
moleculesmolecules

Smear spacing revealsSmear spacing reveals
distance betweendistance between
repeating structuresrepeating structures

Missing smearsMissing smears
indicate interferenceindicate interference
from second helixfrom second helix
www.pbs.org/wgbh/nova/photo51

25. Information Gained from Photo 51Information Gained from Photo 51

Double HelixDouble Helix

Radius: 10 angstromsRadius: 10 angstroms

Distance between bases: 3.4 angstromsDistance between bases: 3.4 angstroms

Distance per turn: 34 angstromsDistance per turn: 34 angstroms
Combining Data with Other InformationCombining Data with Other Information

DNA made from:DNA made from:
sugarsugar
phosphatesphosphates
4 bases (A,C,G,T)4 bases (A,C,G,T)

Chargaff’s RulesChargaff’s Rules
%A=%T%A=%T
%G=%C%G=%C

Molecular ModelingMolecular Modeling
Solving the Structure of DNASolving the Structure of DNA
Watson and Crick’s model

26. DNA MoleculesDNA Molecules
Two polynucleotideTwo polynucleotide
chains are joinedchains are joined
Double helix,Double helix,
twisted in righttwisted in right
handed wayhanded way
Full circle in everyFull circle in every
10 bases10 bases

27. •”ladder-structure”
–Bases = steps
–Sugars and phosphates =
supporting pilars
•Two nucleotide chains
run in opposite directions

28. Complementary PairingComplementary Pairing
Space between the chains is limitedSpace between the chains is limited
Purines with two carbon rings pair only withPurines with two carbon rings pair only with
single ring pyrimidinessingle ring pyrimidines
A + TA + T
G + CG + C
•Interaction is stabilized by
hydrogen bonds

29. Hydrogen bonds
between
complementary
bases
Complementary pairingComplementary pairing
is vital for the use andis vital for the use and
storage of the geneticstorage of the genetic
information!information!