DNA  is a molecule composed of two chains that coil around each other to form a double helix  carrying genetic instructions for the development, functioning, growth and reproduction of all known organism. DNA are nucleic acids;. The two DNA strands are also known as polynucleotides as they are composed of simpler monomeric units called nucleotides. Each nucleotide is composed of one of four nitrogen-containing nucleo bases (cytosine[C], guanine[G], adenine[A] or thymine[T]), a sugar called deoxyribose, and a phosphate group.  Nucleotide :- nitrogenous base,sugar,phosphate Nucleoside :- :- nitrogenous base,sugar

1. varios dna
Name :- Avdhesh kumar
MSc. I sem
Under the guidance of
Dr. Amrita Ku. panda
(Department of Biotechnology)
SANT GAHIRA GURUVISHWAVIDYALAYA,
SARGUJA, AMBIKAPUR, (C.G.)

2. Introduction
DNA is a molecule composed of two chains that coil around each other to
form a double helix carrying genetic instructions for the development,
functioning, growth and reproduction of all known organism. DNA
are nucleic acids;. The two DNA strands are also known
as polynucleotides as they are composed of simpler monomeric units
called nucleotides. Each nucleotide is composed of one of four nitrogen-
containing nucleo bases (cytosine[C], guanine[G], adenine[A]
or thymine[T]), a sugar called deoxyribose, and a phosphate group.
Nucleotide :- nitrogenous base,sugar,phosphate
Nucleoside :- :- nitrogenous base,sugar

5. Phosphate Group
Deoxyribose
Phosphodiester bond
N-glycosyl bond

6. History
DNA was first isolated and characterized by Friedrich Miescher in 1868.
He called the phosphorus-containing substance “nuclein.” Not until the
1940, with the work of OswaldT. Avery, Colin MacLeod, and Maclyn
McCarty, was there any compelling evidence that DNA was the genetic
material. Avery and his colleagues found that DNA extracted from a
virulent (disease-causing) strain of the bacterium Streptococcus
pneumoniae and injected into a nonvirulent strain of the same bacterium
transformed the nonvirulent strain into a virulent strain.They concluded
that the DNA from the virulent strain carried the genetic information for
virulence.Then in 1952, experiments by Alfred D. Hershey and Martha
Chase, in which they studied the infection of bacterial cells by a virus
(bacteriophage) with radioactively labeled DNA or protein, removed any
remaining doubt that DNA, not protein, carried the genetic information.
Another important clue to the structure of DNA came from the work of
Erwin Chargaff and his colleagues in the late 1940s.
They found that the four nucleotide bases of DNA occur in different ratios
in the DNAs of different organisms and that the amounts of certain bases
are closely related.These data, collected from DNAs of a great many
different species, led Chargaff to the following conclusions:

7. The Avery-Macleod-McCarty experiment

8. The Hershey-Chase experiment

9. James Watson and Francis Crick with
their DNA model at the Cavendish
Laboratories in 1953

10. varios dna
 Double DNAs
 Triplex DNAs.
 Tetraplex DNAs,
 Double DNAs
James Watson and Francis Crick relied on this accumulated
information about DNA to set about deducing its structure. In
1953 they postulated a three-dimensional model of DNA structure
that accounted for all the available data. It consists of two helical
DNA chains wound around the same axis to form a right-handed
double
B form DNA
A form DNA
Z form DNA

11. B form DNA
Watson-Crick model for
the structure of DNA. The
original model proposed
by Watson and Crick had
10 base pairs, or 34 Å (3.4
nm), per turn of the helix;
subsequent
measurements revealed
10.5 base pairs, or 36 Å
(3.6 nm), per turn. (a)
Schematic representation,
showing dimensions of
the helix. (b) Stick
representation showing
the backbone and
stacking of the bases. (c)
Space filling model.

13. A form DNA
A-DNA is fairly similar to B-DNA given that it is a right-handed double helix with
major and minor grooves. However, as shown in the comparison table below, there is
a slight increase in the number of base pairs (bp) per turn (resulting in a smaller twist
angle), and smaller rise per base pair (making A-DNA 20-25% shorter than B-DNA).
The major groove of A-DNA is deep and narrow, while the minor groove is wide and
shallow. A-DNA is broader and apparently more compressed along its axis than B-
DNA.
28Å
26Å
B - 11
2.6Å
major
groove minor groove

14. Z-form DNA is a more radical departure from the B structure; the most obvious
distinction is the left-handed helical rotation. There are 12 base pairs per helical
turn, and the structure appears more slender and elongated.The DNA backbone
takes on a zigzag appearance. Certain nucleotide sequences fold into left-
handed Z helices much more readily than others. Prominent examples are
sequences in which pyrimidines alternate with
Z form DNA
45Å
3.7Å
18Å
B - 12

15. Ribofuranose rings in nucleotides can
exist in four different puckered conformations. In all cases, four of
the five atoms are nearly in a single plane. The fifth atom (C-29 or
C-39) is on either the same (endo) or the opposite (exo) side of the
plane relative to the C-59 atom.
Structural variation in DNA. (a) The conformation of anucleotide in DNA is affected by
rotation about seven different bonds. Six of the bonds rotate freely. The limited rotation
about bond 4 gives rise to ring pucker. This conformation is endo or exo, depending on
whether the atom is displaced to the same side of the plane as C-59 or to the opposite side
(see Fig. 8–3b). (b) For purine bases in nucleotides, only two conformations with respect to
the attached ribose units are sterically permitted, anti or syn. Pyrimidines occurin the anti
conformation.

16. Palindromes and mirror repeats. Palindromes are sequences
of double-stranded nucleic acids with twofold symmetry. In order to
superimpose one repeat (shaded sequence) on the other, it must be rotated
1808 about the horizontal axis then 1808 about the vertical axis, as shown
by the colored arrows. A mirror repeat, on the other hand, has a symmetric
sequence within each strand. Superimposing one repeat on the other
requires only a single 1808 rotation about the vertical axis.
Certain DNA Sequences Adopt Unusual Structures

17. FIGURE 8–19 Hairpins and
cruciforms. Palindromic DNA (or
RNA) sequences can form
alternative structures with
intrastrand base pairing. (a) When
only a single DNA (or RNA) strand
is involved, the structure is called a
hairpin. (b)When both strands of a
duplex DNA are involved, it is
called a cruciform. Blue shading
highlights asymmetric sequences
that can pair with the
complementary sequence either in
the same strand or in the
complementary strand.

18.  TriplexDNAs.
In genomic DNA in vivo or in supercoiled plasmid DNA in vitro, homopurine–homopyrimidine tracts with mirror-repeat
symmetry, i.e., AGGAA…AAGGA-TCCTT…TTCCT (top) may form four types of triplex structures: two in which half (either the
5′ or 3′ half; only the 3′ case is shown) of the single-stranded purine-rich strand folds back, engaging in reverse Hoogsteen
interactions with the purine-rich strand of the remaining duplex in an antiparallel orientation (R•R–Y type triplex, left); and
two in which half (either the 5′ or 3′ half; only the 3′ case is shown) of the single-stranded pyrimidine-rich strand folds back,
engaging in Hoogsteen interactions with the purine-rich strand of the remaining duplex in a parallel orientation (or Y•R–Y
type triplex, right). The most common triplets, both in intramolecular and intermolecular (triplex-forming oligonucleotide
[TFO]-derived) triplexes, include A•A–T, G•G–C, and T•A–T for R•R–Y type triplexes (bottom left), and C+•G–C and T•A–T for
Y•R–Y type triplexes (bottom right). C+ indicates a protonated cytosine.

19. Reference :- G-quadruplex DNA: A target for drug design Jean-
Louis Mergny & Claude Hélène
Tetraplex DNA and its interacting proteins
Michael Fry
Tetraplex DNAs
B. Scheme of the
three major classes of quadruplex DNA.The illustrated
quadruplexes are stabilized by quartets formed between
two clusters of three contiguous guanine residues each.The
G'4 unimolecular and G'2 bimolecular tetraplexes are
shown as having antiparallel orientation and the G4
fourmolecular
tetraplex as a parallel-stranded tetrahelix.
Notably, however, G'4 and G'2 quadruplexes can also adopt
parallel-stranded polarity

21. Conclusion
 DNA is a molecule composed of two chains that coil around
each other to form a double helix
 carrying genetic instructions for the development, functioning,
growth and reproduction of all known organism.

22. Reference
 Lehninger sixth edition principles of biochemistry David L.
Nelson Michael M.cox
 New Perspectives on DNA and RNATriplexes As Effectors
of Biological Activity
Albino Bacolla,
Guliang Wang,
Karen M.Vasquez
 Tetraplex DNA and its interacting proteins Michael Fry
 G-quadruplex DNA: A target for drug design
Jean-Louis Mergny &
Claude Hélène