Definition:
⇒ The
particles in nucleus of a cell, responsible for heredity, are called
chromosomes which are made up of proteins and nucleic acids.
⇒ Nucleic
acids are long chain polymers of nucleotides, so they are also called
polynucleotides.
⇒ Examples:
Deoxyribonucleic acid (DNA) & Ribonucleic acid (RNA).
Chemical Composition of Nucleic Acids:
⇒ Each nucleotide has three components: a 5 - carbon sugar, a phosphate group, and a nitrogenous
base.
⇒ In
DNA molecules, the sugar moiety is β - D - 2 - deoxyribose where as in RNA
molecule, it is β - D - ribose.
⇒ DNA
contains four bases viz. adenine (A), guanine (G), cytosine (C) and thymine
(T).
⇒ RNA
also contains four bases, the first three bases are same as in DNA but the fourth
one is uracil (U).
Structure of Nucleic Acids:
⇒ A
unit formed by the attachment of base to 1’ position of sugar is known as
nucleoside, the sugar carbons are numbered as 1’, 2’, 3’, etc. in order to
distinguish these from bases. When nucleoside is linked to phosphoric acid at
5’ - position of sugar moiety we get a nucleotide.
⇒ Nucleotides
are joined together by phosphodiester linkage between 5’ and 3’ carbon atoms of
pentose sugar.
⇒ A
simplified version of nucleic acid chain is as shown below.
⇒ Information
regarding the sequence of nucleotides in the chain of nucleic acid is called
primary structure. Nucleic acids have a secondary structure also.
⇒ James
Watson and Francis Crick gave a double strand helix structure for DNA. Two
nucleic acid chains are wound about each other and held together by hydrogen
bond between pairs of bases.
⇒ These
are complementary to each other because the hydrogen bonds are formed between
specific pairs of bases.
DNA Fingerprinting:
⇒ Every
individual has unique fingerprints.
⇒ A
sequence of bases on DNA is also unique for a person and information regarding
this is called DNA fingerprinting.
⇒ It
is same for every cell and cannot be altered by any known treatment.
Uses of DNA finger printing:
i)
In forensic laboratories for identification of criminals.
ii)
To determine paternity of individual
iii)
To identify racial groups to rewrite biological evolution.
Biological functions of Nucleic acids:
⇒ DNA
is the chemical basis of heredity and may be regarded as the reserve of genetic
information.
⇒ DNA
is responsible for maintaining the identity of different species of organisms
over millions of years.
⇒ A
DNA is capable of self-duplications during cell division and identical DNA
strands are transferred to daughter cells.
⇒ Nucleic
acids are responsible for protein synthesis in the cell.
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