DNA is a double-stranded molecule composed of nucleotides that contain nitrogenous bases, a deoxyribose sugar, and a phosphate group. The bases--cytosine, thymine, adenine, and guanine--form rungs of a twisted ladder structure, while the alternating sugar and phosphate molecules form the sides. Watson and Crick discovered that the bases pair up specifically through hydrogen bonds to form the DNA double helix, which contains the genetic information needed to build an organism. DNA can take on different secondary structures including A-DNA, B-DNA, and Z-DNA forms.

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2. INTRODUCTION OF DNA
• DNA is a double stranded molecule that is
twisted into a Helix
• DNA are macromolecular structures
composed of regular repeating polymers
formed from nucleotides.
• DNA is a complex molecule that contains of
the information necessary to build and
organism

3. COMPONENTS
OF NUCLOTIDE
Nitrogenous Bases
Deoxyribose Sugar
Phosphate Group
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4. NITROGENOUS
BASE
CYTOSINE
THYMINE
ADENINE GUANINE
• CYTOSINE
• THYMINE
PYRIMIDINE
• ADENINE
• GUANINE
PURINE
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5. DEOXYRIBOSE
SUGAR
• The sugars found in
nucleic acids are pentose
sugar ; a pentose sugar
has five carbon atoms.
• Deoxyribose, found in
DNA , is a modified
sugar , lacking one
oxygen atom (hence the
name “deoxy”).
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6. PHOSPHATE
GROUP
• A phosphate group is
just a phosphorus atom
bound to four oxygen
atoms , but it has many
important roles.Along
with sugars and bases, it
makes up nucleic acids.
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7. THE SECONDARY
STRUCTURE OF DNA
• The sides of the ladder are made up of
alternating molecules of phosphate
and deoxyribose.
• The bases make up the rungs of the
ladder are attracted by a weak
chemical bonds called hydrogen
bonds.
Watson and Crick Model
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8. A-DNA
• A-DNA is one of the many possible double helical structures of
DNA.
• It is most active along with other forms.
• Shorter more compact helical structure.
• Such as those used in crystallographic experiments.
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9. B-DNA
• Helical sense : right handed.
• Base pairs : almost perpendicular to the ,helix axis ; 3.4
angstrom apart.
• One turn of the helix : 36 angstrom; which is equals to 10.4
base pairs. 9

10. Z-DNA
• Z-DNA is one of the many possible double helical structures of DNA.
• Helix has left-handed sense.
• It is most active double helical structure.
• Z-DNA was first discovered in 1979,certain proteins bind very strongly to
Z-DNA.
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