Deoxyribonucleic Acid
DNA (Deoxyribonucleic Acid) is hereditary material. It packed
very tightly and perfectly to form a chromosome. DNA is the most important
molecule in organisms
Constituents of DNA
As
the DNA is a chemical, DNA is quite simple. It contains three types of chemical
components
1) A deoxyribose Sugar,
2) A nitrogenous base,
3) A phosphate group.
1. Deoxyribose Sugar
The sugar in the DNA is called deoxyribose because it has only H atom at 2’ Carbon, unlike ribose which has (OH) at 2’ Carbon atom.
Ribose is a
single-ring pentose [5-Carbon] sugar. The numbering of the carbon atoms runs
clockwise, following organic chemistry rules. Note the absence of the hydroxyl
(-OH) group on the 2’ carbon in the deoxy-ribose sugar in DNA as compared with
the ribose sugar in RNA
There are four nitrogenous bases present in the DNA, i.e. two purines (Adenine, Guanine), and two Pyrimidine (Cytosine, Thymine). For the convenience the carbon atoms in the Nitrogenous base are numbered as 1, 2, 3, and so on.
And the carbon atoms in the sugar are numbered by the same way but assigned with a prime (2’, 3’, and so on).
Purines are double ring structures; there are two purines present in DNA. Adenine and Guanine.
3. Phosphate group
It’s
derived from phosphoric acid (H3PO4).
Phosphorus
attached to the four Oxides (PO4)-3. And - 3 charges is
present at this group.
Nucleoside
and Nucleotide
When the
deoxy ribose sugar and any of the four nitrogenous base joins together through
a N-Glycosidic bond it is called as Nucleoside.
Sugar +
Nitrogenous base = Nucleoside
When a
phosphate group joins the nucleoside through phosphodiester bond, this
structure is known as Nucleotide.
Sugar +
Nitrogenous base +Phosphate group = Nucleotide
The
Nucleotides joins together to form large molecule of DNA. It is convenient to
write the first capital letter of the each nucleotide as A, G, C, T.
The
nucleotide with adenine base names as “deoxyadenosine 5’-monophosphate”. 5’ is
actually the position on sugar where the phosphate group attached.
Chargaff’s rules
Chargaff
most importantly determining the structure of the DNA. He formulated about the
base composition of the DNA.
1. The whole quantity of Pyrimidines is often adequate to the whole
quantity of Purines.
2. The quantity of “A” is often adequate to the quantity of “T”. And quantity of “G” is adequate to the
quantity of “C”. However the amount of (A+T) not basically equals to the
quantity of (G+C).
3. This quantitative relation varies within the totally different
organisms however same within the same organisms
X-Ray Diffraction information
Rosalind Franklin
collected this information. X-rays were dismissed on the Deoxy ribonucleic
acid, the scattered light-weight is determined through film. It showed spots
made by X-rays. The angle of those sports gave info regarding the position of
the atoms within the DNA. It absolutely was demonstrated; the DNA is long and
has 2 similar components parallel to every alternative. It additionally
instructed that the DNA has coiling structure.
The helix model of Structure
Watson and Crick in 1953 revealed the
planned structure of DNA in the journal Nature. The 3 dimensional structure
planned by them has 2 strands that runs parallel to every alternative. They’re
composed of nucleotides, and twisted along to make a helix structure.
The two ester
strands nucleotide stick along by weak interactions of H bonding. The back bone
is formed of sugar and phosphates as an alternative, whereas the N- bases
protrude outward from the back bone. The every sugar-phosphate back bone is
3’-5’. Each the strands lie opposite one another other i.e. opposing parallel.
Every base is connected to the 1’ carbon of the deoxy sugar, and faces inward
N-base on the opposite strand. H bonds between the bases of 2 strands hold the
2 strands of polymer. Stacking of N-base pairs happens. This stacking adds the
soundness to the DNA molecule. By double coiled structure 2 grooves square
measure fashioned one is Major groove the opposite is Minor Groove.
Purine base
continuously pair up with pyrimdine base. A pair up with T and C combines with
G.
There is three H-
bonds gift between G-C bases. And a couple of H- bonds gift between A-T bases.
Hence the deoxyribonucleic acid with a lot of G-C pairs are
stable than the one with a lot of A-T pairs.
Forms
of DNA
B-Form DNA
It is the
foremost common style of the DNA. It’s the conventional minor and major
grooves.
It has
dimensions
•0.34 nm between bp, 3.4nm per
flip, regarding ten bp per flip
•1.9 nm in diameter
•It is traditional right handed
structure
Z-form DNA
•It is left handed double coiling
structure
•The major and minor grooves very
little distinction
A-Form DNA
•It could be a right handed structures
•Has shorter and additional compact coiling structure
1 Comments
Well explained
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