By Jimcale Hamari

1. DNA Structure
Jimcale Mohamed Ali

2. DNA Structure
• DNA is un-branched linear polymer of nucleotides.
Components
• Nitrogenous base
• Purine (Adenine and Guanine)
• Pyrimidine (Cytosine and Guanine)
• Pentose sugars
• Deoxyribose
• Phosphates

3. Two Kinds of Bases in DNA
• Pyrimidines are
single ring bases.
• Purines are double
ring bases.
C
C
C
C
N
N
O
N
C
C
C
C
N
N
N
N
N
C

4. Nitrogenous Bases
PYRIMIDINES
PURINES

5. Nucleoside

6. Nucleotide

7. Nucleotides and Nucleosides
O
C C
C C
Base
H
H H
H
H
CH2OP
OH
O
HO
Nucleotide: a building block
Sugar:
• RNA – ribose (OH)
• DNA – deoxyribose (H)
Bases:
• adenine (A), cytosine (C), guanine (G),
thymine (T)
Nucleoside: base + sugar
• certain nucleotides serve as a storage of energy and reducing power
e.g. ATP -> ADP -> AMP
hydrolysis (energy is released)

8. Nucleotides and Nucleosides
BASE NUCLEOSIDE
Adenine Adenosine
Guanine Guanosine
Cytosine Cytodine
Thymine Thymidine
Nucleotides are nucleosides + phosphate

9. Chemical Structure of DNA
Nucleotide
Nucleoside

10. DNA Stabilization– Complementary
Base Pairing

11. DNA Stabilization--H-bonding
between DNA base pair stacks

12. Advantages to Double Helix
• Stability---protects
bases from attack by
H2O soluble
compounds and
H2O itself.
• Provides easy
mechanism for
replication

13. Physical Structure

14. Forms of DNA

15. Denaturation of DNA
The T at which ½ the DNA
sample is denatured is
called the melting
temperature (Tm)

16. Importance of Tm
• Critical importance in any technique that
relies on complementary base pairing
– Designing PCR primers
– Southern blots
– Northern blots
– Colony hybridization

17. Factors Affecting Tm
• G-C content of sample
• Presence of intercalating agents (anything that
disrupts H-bonds or base stacking)
• Salt concentration
• pH
• Length

18. Renaturation
• Strands can be induced to renature (anneal) under
proper conditions.
• Factors to consider:
– Temperature
– Salt concentration
– DNA concentration
– Time