Structure of DNA: *helically twisted double chain polydeoxyribonucleotide macromolecule. * Procaryotes occur in Nucleoid and Plasmids. * Eucaryotes found in Chromatid of nucleus. * Smaller quanitites found in Mitochondria and Plastids. *Single-stranded DNA occurs as a genetic material in some viruses (e.g., coli-phage ф x 174). *DNA is the largest macromolecule with a diameter of 2 nm (20A) and having a length in millimeters. * It may be circular or linear. *It is a long chain polymer of several hundred thousands of deoxyribonucleotides, e.g., 4.7 million base pairs in E.coli and more than 3 billion base pairs in human being. *The two strands are not coiled upon each other but double strand is coiled upon itself around a common axis like a rope or spiral stair case with base pairs forming steps (rungs) while the back bones of the two strands form railings. * Due to spiral twisting, the DNA duplex comes to have two types of alternate grooves, major and minor. *One turn of 360° of the spiral has about 10 nucleotides on each strand of DNA. * It occupies a dis­tance of about 3.4 nm (34A) Various forms of DNA Functions of DNA: Functions of DNA: (1) DNA is genetic material which carries all the hereditary information coded in the arrangement of its nitrogen bases. (2) It has the property of replication (autocatalytic func­tion) essential for passing genetic information from one cell to its daughters or from one generation to the next. (3) Crossing over produces re-combinations. (4) Changes in sequence and number of nucleotides produce mutations. Mutations are the fountain head of all varia­tions and formation of new species. (5) It gives rise to RNAs through transcription (Heterocatalytic function). (6) DNA controls the metabolic reactions of cells through RNAs and RNA-directed synthesis of proteins, enzymes and other bio-chemicals. (7) Differ­entiation of various body parts is due to differential functioning of specific parts of DNA. (8) Developmental stages occur in the life cycle of an organism by an internal clock of DNA functioning.

1. Structure of DNA
and
Various forms of dna
By
SATHYA.T,
MSC Microbiology(2017-2019)
Tirupur Kumaran College For Women,
Tirupur
Tamil Nadu.

2. Structure of DNA:
*helically twisted double chain
polydeoxyribonucleotide macromolecule.
* Procaryotes occur in Nucleoid and Plasmids.
* Eucaryotes found in Chromatid of nucleus.
* Smaller quanitites found in Mitochondria and
Plastids.
*Single-stranded DNA occurs as a genetic
material in some viruses (e.g., coli-phage ф x 174).
*DNA is the largest macromolecule with a
diameter of 2 nm (20A) and having a length in
millimeters.
* It may be circular or linear.

5. *It is a long chain polymer of several hundred thousands of
deoxyribonucleotides, e.g., 4.7 million base pairs in E.coli and
more than 3 billion base pairs in human being.
*The two strands are not coiled upon each other but
double strand is coiled upon itself around a common axis like
a rope or spiral stair case with base pairs forming steps (rungs)
while the back bones of the two strands form railings.
* Due to spiral twisting, the DNA duplex comes to have
two types of alternate grooves, major and minor.
*One turn of 360° of the spiral has about 10 nucleotides on
each strand of DNA.
* It occupies a distance of about 3.4 nm (34A)

7. *A deoxyribonucleotide of DNA is formed by cross-
linking of three chemicals—phosphoric acid (H3PO4),
deoxyribose sugar (C5H10O4) and a nitrogen base.
Four types of nitrogen bases occur in DNA.
*DNA has two types of purines (adenine or A and
guanine or G) and two types of pyrimidine’s (cytosine or С
and thymine or T).
*Depending upon the type of nitrogen base, DNA has
four kinds of deoxyribonucleotides —
1)deoxy-adenosine 5-mono- phosphate (d AMP)
2)deoxy guaninosine 5-monophosphate (d GMP)
3)deoxy thymidine 5-monophosphate (d TMP)
4)deoxy cytidine 5-monophosphate (d CMP).

19. Functions of DNA:
(1) DNA is genetic material which carries all the hereditary information coded
in the arrangement of its nitrogen bases.
(2) It has the property of replication (autocatalytic function) essential for
passing genetic information from one cell to its daughters or from one
generation to the next.
(3) Crossing over produces re-combinations.
(4) Changes in sequence and number of nucleotides produce mutations.
Mutations are the fountain head of all variations and formation of new species.
(5) It gives rise to RNAs through transcription (Heterocatalytic function).
(6) DNA controls the metabolic reactions of cells through RNAs and RNA-
directed synthesis of proteins, enzymes and other bio-chemicals.
(7) Differentiation of various body parts is due to differential functioning of
specific parts of DNA.
(8) Developmental stages occur in the life cycle of an organism by an internal
clock of DNA functioning.