DNA is a double-stranded molecule composed of repeating nucleotides that form a helical structure and contains the genetic information of organisms. Nucleotides consist of a nitrogenous base, a pentose sugar called deoxyribose, and a phosphate group. The two strands of the DNA double helix are held together by hydrogen bonds between complementary purine bases adenine (A) and guanine (G) and pyrimidine bases thymine (T) and cytosine (C). Different DNA structures include A-DNA, B-DNA, and Z-DNA which vary in their helical sense, base pair orientation, and groove size.

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2. Introduction Of DNA
all
maintain an
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
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3. Components of a nucleotide
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4. Nitrogenous bases
Basic structure
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5. Pyrimidines
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6. Purines
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7. Sugar
Deoxyribose sugar
The sugars found in nucleic acids are pentose sugars; 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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8. 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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9. Phosphate
Sugar
Base
Nucleoside
Nucleotide
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X=H: DNA
X=OH: RNA

10. Types of DNA
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ADNA
B DNA
Z DNA

11. A-DNA
A-DNA is one of the many possible double helical structures of
DNA.
It is most active along with other forms.
Helix has right-handed sense,
shorter more compact helical structure.
It occurs only in dehydrated samples of DNA,
such as those used in crystallographic experiments.
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12. B- DNA
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Helical sense: right handed.
Base pairs :almost perpendicular
to the, helix axis; 3.4 Å apart.
One turn of the helix: 36 Å;
~10.4 base pairs.
Minor groove: 12 Å across.
Major groove: 22 Å across.

13. Z-DNA
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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.

14. Types of DNA
Property A-DNA B-DNA Z-DNA
Helix Handedness Right Right Left
Base Pairs per turn 11 10.4 12
Rise per base pairalong
axis
0.23nm 0.34nm 0.38nm
Pitch 2.46nm 3.4nm 4.56nm
Diameter 2.55nm 2.37nm 1.84nm
Major Groove Present Present Absent
Minor Groove Present Present Deep Cleft
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15. DNA Primary structure
3’end
5’end
5’
3’
Phosphodiester
linkage
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16. The secondary structure of
DNA
Watson and Crick Model:
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.
The DNA double helix is anti-parallel,
which means that the 5' end of one strand is
paired with the 3' end of its complementary
strand (and vice versa).
5' >3‘
3'< 5'
Two hydrogen bonds connect T to A; three
hydrogen bonds connect G to C.
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17. The secondary structure of
DNA is the double helix
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