DNA is a double-stranded molecule that forms a helical structure. It is composed of nucleotides, each containing a phosphate group, deoxyribose sugar, and a nitrogenous base. There are two types of bases: purines (adenine and guanine) and pyrimidines (cytosine and thymine). The bases form rungs that link the strands via hydrogen bonds between adenine-thymine and guanine-cytosine. DNA exists in three primary structures - A-DNA, B-DNA, and Z-DNA - which differ in their helical geometry and handedness. The main role of DNA is long-term information storage in the genome that is used for building and maintaining

1. Presented To: Presented By:
S.O.S. in Microbiology Anurag Gupta
Jiwaji University, Gwalior M.sc 1St Semester
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2. Content
1. Introduction
2. Components
3. Structure of DNA
4. Types of DNA
5. Bibliography
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3. 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 all
of the information necessary to build and maintain an
organism
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5. Components of a nucleotide
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•
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6. Nitrogenous bases
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Basic structure

7. Pyrimidines
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8. Purines
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9. 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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10. 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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11. 11
Phosphate
Sugar
Base
Nucleotide
Nucleoside
X=H: DNA
X=OH: RNA

12. Nomenclature of Nucleic Acid
Components
 Purines
 Pyrimidines
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Base Nucleoside Nucleotide
Adenine Deoxyadenosine Deoxyadenylate
Guanine Deoxy guanosine Deoxyguanylate
Base Nucleoside Nucleotide
Cytosine Deoxycytidine Deoxycytidylate
Thymine deoxythymidine deoxythymidylate

13. DNA Primary structure
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3’ end
5’ end
5’
3’
Phosphodiester
linkage

14. 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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15. The secondary structure of
DNA is the double helix
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16. Types of DNA
 A DNA
 B DNA
 Z DNA
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17. 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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18. B- DNA
 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.
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19. 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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20. 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 pair along
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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21. Function of DNA
 Scientists have since discovered that certain proteins
bind very strongly to Z-DNA, suggesting that Z-DNA
plays an important biological role in protection against
viral disease.
 The main role of DNA in the cell is the long-term storage of
information
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22. Recent work
 The transformation of the DNA template in
RNA polymerase II transcription: James T.
Kadonaga on 22-08-2019
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23. Bibliography
 Principals and techniques of biochemistry and molecular
biology 7th edition-Wilson & walker(page no 139)
 Principle of Biochemistry –David .L . Nelson &
Michael .M. Cox(Chapter 8.Nucleotides)
 https://www.nature.com/scitable/topicpage/introduction-
what-is-dna-6579978/
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