DNA
(Deoxy ribose nucleic acid)
DNA is a chemical in the chromosomes which carries the
heredity information of the cell. DNA carries the code used by the cell
while making proteins. Every chromosomes contains one molecule
DNA and genes are the segments of DNA. DNA was first isolated by
the scientist, Frederick Meisher from the nucleus of the pus cells in
1869. It was named as nuclein or nucleic acid because of its acidic
nature.
DNA is the genetic material in all the organism. Some
viruses do not contain DNA. So, in some viruses, RNA is the genetic
material. A virus having RNA as the genetic material is known as
retrovirus. The AIDS virus called human immodeficiency virus (HIV)
is retrovirus.
DNA is made up of a large number of smaller units called
nucleotide units. So DNA is a polynucleotide. Nucleotide is the basic
structural unit of DNA.
Nucleotide is a compound made of three components:-
(i) a nitrogen base
(ii) deoxyribose Sugar
(iii) a phosphate molecule
(a) A nitrogen base – There are four types of
nitrogen bases in DNA.
(i) Adenine
(ii) Guanine
(iii) Cytosine
(iv) Thymine
STRUCTURE OF DNA –
The structure of DNA was discovered by Watson and crick. For
this they were awarded Nobel Prize in 1962. DNA is long chain
polymer of deoxyribonucleotides, which are arranged in two helical
strands held together by weak hydrogen bonds between the bases of
adjoining strands.
Each helical turn has a length of 3.4 nm in which ten nucleotides
are present.
The deoxyribose sugar molecules are linked together through
phosphate groups.
The phosphate groups of two neighbouring nucleotides are
connected by phospodiester bonds.
To the sugar molecule is attached a nitrogenous purine or
pyrimidine base.
The bases always link together in adjoining strands of the DNA
molecule in the following sequence
Adenine and thymine are held together by a double hydrogen
bonds where as cytosine and guanine are held together by a
triple hydrogen bonds.
Base pairs are complimentary nitrogen bases present on the two
DNA strands with a purine lying opposite a pyrimidine or vice
versa.
Adenine will pair only with thymine where as cytosine will pair
always with guanine.
The two DNA strands are complementary and antiparallel to
each other.
FUNCTION OF DNA -
DNA is genetic material which carries all the hereditary
information.
DNA can replicate itself and pass genetic information from one
cell to its daughter cells.
DNA controls the metabolic activities in the body.
DNA AND GENETICS ENGINEERING
The two strands of DNA are complimentary to each other. The
DNA strand can be cut with the help of a specific enzyme (restriction
endonuclease), and then it can be joined ( by ligase enzyme ) or
attached with the DNA of a different organism.
The organisms that contain a segment of foreign DNA or gene
are known as transgenic organism or genetically modified organism
(GMO).
We wish to express our deep sense of
gratitude and sincere thanks to our teacher Mr.
Ajay Goel for his invaluable guidance rendered
for the successful completion of this project.
In the end we express my hearties thanks to
all whose directly and indirectly took interest in
the project and have provided guidance to us.
SUBMITTED BY
Ayush Jain
IXth B
This is to certify that Ayush Jain of class
IXth B has completed the project entered on
“Congruence of Triangles”. It is the
result of student own hard work carried out
by him under my supervision and guidance.
Mr.
Ajay Goel
AIM
The aim of my project is that to get knowledge about
“DNA” and its characteristics and its applications.
Session – 2006-07
Submitted to :
Submitted by :
Mr Ajay Goel
Ayush Jain
IXth B
