for video: https://youtu.be/B4758Hb3wwE
DNA, the genetic material of most of living organism. herein, we will discuss about its discovery, its components and structural detail
2. Nucleic acids were first isolated by Friedrich Miescher (1869) from pus cells, named nuclein.
Hertwig (1884) proposed nuclein to be the carrier of hereditary traits.
Altmann, 1899 called it nucleinic acids and then nucleic acids because of their acidic nature.
Fisher (1880s) discovered the presence of purine and pyrimidine bases in nucleic acids. Levene (1910)
found deoxyribose nucleic acid to contain phosphoric acid as well as deoxyribose sugar.
In 1950, Chargaff found that purine and pyrimidine content of DNA was equal.
W.T. Astbury had found through X-ray diffraction that DNA is a polynucleotide with nucleotides
arranged perpendicular to the long axis of the molecule and separated from one another by a distance
of 0.34 nm.
In 1953, Wilkins and Franklin got very fine X-ray photographs of DNA.
Watson and Crick (1953) worked out the first correct double helix model from the X-ray photo-
graphs of Wilkins and Franklin.
Wilkins, Watson and Crick were awarded Nobel Prize for the same in 1962.
3. Nucleic acids are the organic materials present in all
organisms in the form of DNA or RNA.
These nucleic acids are formed by the combination of :
(a) nitrogenous bases
(b)sugar
(c)phosphate groups that are linked by different bonds in a
series of sequences.
The DNA structure defines not only the basic genetic
makeup of our body but nearly all life on earth.
4. The nitrogenous bases are:
A. Purines:
Adenine (A) and Guanine (G)
B . Pyrimidines:
Cytosine (C), Thymine (T), and
Uracil (U).
Sugar:
Sugar: A nucleotide comprises a
pentose sugar.
DNA (Deoxyribonucleic acid)
contains deoxyribose sugar and
RNA (Ribonucleic acid) contains a
ribose sugar.
5. A Nitrogenous base
attached with the sugar
is called “Nucleoside”.
Nucleoside =
Nitrogenous base +
Sugar
Nucleosides are named as
Adenosine, Guanosine,
Thymidine, Cytidine,
Uridine
Nucleoside with phosphate
is called as Nucleotide.
6.
7. 1. DNA is made of two
helical chains coiled around
the same axis, to form a
right-handed double helix.
2. The two chains in the
helix are anti-parallel to
each other, i.e., the 5′-end
of one polynucleotide chain
and the 3′-end of the other
polynucleotide chain is on
the same side and close
together.
3. The distance between
each turn is 3.6 nm
(formerly 3.4 nm).
4. There are 10.5 nucleotides
per turn (formerly 10
nucleotides).
8. 5. The spatial
relationship between the
two strands creates
major and minor grooves
between the two strands.
In these grooves some
proteins interact.
6. The hydrophilic
backbones of
alternating deoxyribose
and negatively charged
phosphate groups are on
the outside of the double
helix.
9. 8. The double helix is also stabilized by
inter-chain hydrogen bond formed
between a purine and pyrimidine base.
9. A particular purine base, pairs by
hydrogen bonds, only with a particular
pyrimidine base, i.e., Adenine (A) pairs
with Thymine (T) and Guanine (G) pairs
with Cytosine (C) only.
10. Two hydrogen bonds pairs Adenine and
Thymine (A = T), whereas three hydrogen
bonds pairs Guanine and Cytosine (G ≡ C).
7. The hydrophobic pyrimidine and purine
bases are inside the double helix, which
stabilizes the double helix of the DNA.
10. 11. The base pairs A = T and G ≡ C are
known as complementary base pairs.
12. Due to the presence of complementary
base pairing, the two chains of the DNA
double helix are complementary to each
other.
13. The template strand is the one that RNA
polymerase uses as the basis to build the RNA.
This strand is also called the non-coding
strand or the antisense strand.
The non-template strand has the identical
sequence of the RNA (except for the
substitution of U for T). This strand is also
called the coding strand or sense strand.
