1. NUCLEIC ACID STRUCTURE
DNA and RNA are large macromolecules with several levels of complexity
Nucleotides form the repeating units
Phosphodiester bonds link nucleotides to form a strand
Two strands interact to form a double helix
The double helix interacts with proteins resulting in 3-D structures in the form of chromatin
3D structure

2. Nucleotide Components
Figure 9.8
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3. Combining all the parts
Base + sugar  nucleoside
Example
Adenine + ribose = Adenosine
Adenine + deoxyribose = Deoxyadenosine
Base + sugar + phosphate(s)  nucleotide
Adenosine monophosphate (AMP)
Adenosine diphosphate (ADP)
Adenosine triphosphate (ATP)
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4. 9-28 Figure 9.10 Base always attached here
Phosphates are attached there
Figure 9.10
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5. Figure: 10-08
Caption:
Structures and names of the nucleosides and nucleotides of RNA and DNA.

6. Figure: 10-09
Caption:
Basic structures of nucleoside diphosphates and triphosphates, as illustrated by thymidine diphosphate and adenosine triphosphate.

7. dNMP
NMP
A, G, C or T
A, G, C or U
Figure 9.9
The structure of nucleotides found in (a) DNA and (b) RNA
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8. Nucleotide Polymerization Reaction: Phosphodiester Bond Formation
Figure: 11-08
Caption:
Demonstration of 5’-to-3’ synthesis of DNA.

9. Figure 9.11
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10. Events Leading to DNA Structure Determination
1953, James Watson and Francis Crick discovered the double helical structure of DNA
The scientific framework for their breakthrough was provided by other scientists including
Linus Pauling
Rosalind Franklin
Erwin Chargaff
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11. Linus Pauling

12. Rosalind Franklin
Helical
Double stranded
10 base pairs per turn

13. X-ray Diffraction Pattern of DNA

14. Erwin Chargaff’s Experiment
It was assumed the four bases: A, G, C and T were in a repeating, tetranucleotide configuration
Therefore, there should be the same amount of A, G, C & T in any molecule of DNA form any source
Chargaff carefully determined the exact percentages of nuceotides in DNA from several sources
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15. Erwin Chargaff’s Data % A = % T & %G = %C However %AT DID NOT = %GC
This observation became known as Chargaff’s rule
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16. Watson & Crick Model DNA Structure

17. Base Pairing Key to DNA Structure

18. Features of the DNA Double HelixNH 2 T
2 nm
One nucleotide
0.34 nm
One complete
turn 3.4 nm O H N P O–
NH2 OH
H2N HO
5¢ end
3¢ end
3¢ hydroxyl
5¢phosphate A S C G
CH2
CH3

19. Features of the DNA Double Helix
Minor
groove
Minor
groove
Major
groove
Major
groove
Ball-and-stick model of DNA
Space-filling
model of DNA

20. Major Helical Conformations of DNA
A-DNA
B-DNA

21. Melting Point Curve: Tm is Proportional to %GC
Figure: 10-14
Caption:
Increase in UV absorbance and temperature (the hyperchromic effect) for two DNA molecules with different G[triple bond]C contents. The molecule with a melting point (Tm) of 83°C has a greater G[triple bond]C content than the molecule with a Tm of 77°C.
Tm= (0.41)(%GC)

22. The Three-Dimensional Structure of DNA
Figure 9.21
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23. RNA Structure
The primary structure of an RNA strand is much like that of a DNA strand
RNA is made as a single strand only, however it may form a double stranded structures
RNA strands can be a 10s to1000s of nt in length
RNA is made from a DNA template - only one of the two strands of a DNA helix is used as the template
RNA contains uracil rather than thymine
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24. Figure 9.22
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25. RNA Secondary Structures
Figure 9.23
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26. RNA Tertiary Structure – a tRNA
Figure 9.24
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