NUCLEIC ACIDS
Definition
They
were discovered by Friedrich Mischer in 1869.
Nucleic acids are biopolymers or
long-chain polymeric molecules having high molecular weight, with
the monomer (the repeating unit) known as the nucleotides and hence
sometimes nucleic acids are referred to as polynucleotides.
OR
The macromolecules which are
formed by the polymerization of nucleotides (monomers) are called
nucleic acid. The nucleic acids are the long chain polynucleotide in
which mononucleotides (monomers) are linked with each other.
Constituent Elements
They contain elements like carbon,
hydrogen, oxygen, nitrogen and rarely phosphorus.
Importance
Nucleic
acids are essential components of every living cell. (Cancer is caused by
damage to DNA or interfering with the mechanism of its replication or passing
information. So by understanding the mechanism of action of DNA, cancer can be
cured). Nucleic acids are biopolymers and are most important of all
biomolecules because they store and transmit hereditary information from
parents to children. In living organisms, even single fertilized egg carries
the information for making the different organs like heart, liver eyes, kidneys,
hands, legs, heads etc.
Occurrence
They
are present in all organisms either in the free state or bound to proteins as nucleoproteins.
DNA is found mainly in the chromatic of the cell nucleus whereas about
90% of the RNA is present in the cell cytoplasm and only 10% occurs in
the nucleolus.
Importance
of Nucleic Acid
1. They are the most vital material for
cell functioning.
2. They are the storage of genetic
information.
3. They work for mutation to save
the cells and body form threatening diseases.
4. They transfer heredity characters
from one generation to another generation.
5. They serve as a source of energy
in the form of ATP.
6. They are
responsible for the synthesis of protein in our body
7. DNA fingerprinting is a method used by forensic
experts to determine paternity. It is also used for the identification of
criminals. It has also played a major role in studies regarding biological
evolution and genetics.
Composition of Nucleotide
Each nucleotide consists of three components; nitrogenous
base (purines and pyrimidines), a pentose sugar (ribose or deoxyribose) and a
phosphate group. The chemical linkage between monomer units in nucleic acids is a
phosphodiester.
Each nucleotide consists of three
components;
1. A heterocyclic nitrogenous base or nucleobase
(purines and pyrimidines),
2. A five carbon pentose sugar
(either deoxyribose, C5H10O4 in DNA and
ribose, C5H10O5 in RNA)
3. A phosphate group (phosphoric
acid; H3PO4)
The two basic types of nitrogenous
bases are double ringed purines and single ringed pyrimidines.
Purines (pure as Ag) includes two nitrogenous bases like Adenine (A) [6-amino
purine] and Guanine (G) [2-amino-6-oxy purine) while pyrimidines include three
nitrogenous bases like Cytosine (C) [2-oxy-4-amino pyrimidine], Thymine (T)
[2,3-dioxy-5-methylpyrimidine]and Uracil (U) [2,3-dioxypyrimidine]. [When small
ring is cut, we get pyrimidine bases CUT)
There are five nitrogen bases that are
found in nucleic acids. Adenine, guanine, thymine and cytosine are found in
DNA, whereas, Adenine, guanine, cytosine and uracil are found in RNA.
These nitrogen bases pair up very specifically and are held together by weak
hydrogen bonds. Adenine always pairs up with thymine by two hydrogen bonds while
guanine pairs up with cytosine with three hydrogen bonds.
Adenine pairs with both thiamine and uracil. Adenine forms two hydrogen bonds with thiamine in DNA and with uracil in RNA.
Difference between RNA and DNA
The type of pentose sugar
differentiates RNA with DNA. RNA contains ribose sugar while DNA contains
deoxyribose sugar. The phosphoric acid is common in all nucleotides and it is
attached with 5th carbon of pentose sugar. The pentose sugar and
phosphoric acid behave as basic skeleton.
DNA is
a polynucleotide chain in which nucleotides are arranged in a specific manner
containing common phosphate and deoxyribose sugars but different nitrogenous
bases having specific sequence. These sequences of bases in DNA can encode vast
amount of information. The four different types of bases can be arranged in any
linear order along a DNA strand. Each sequence of bases represents a unique set
of genetic instructions. E.g. a piece of DNA with 10 nucleotides can exist in
over a million different possible sequences of four bases. An average
chromosome of plant and animal has millions to billions of nucleotides and DNA
molecules encodes a huge amount of information in the form of genetic codes.
Comparing
DNA to RNA
1. DNA contains deoxyribose sugar (C5H10O4)
while RNA carries ribose sugar (C5H10O5) in
their nucleotides.
2.DNA contains nitrogenous bases like
adenine, guanine, cytosine and thymine whereas RNA contains adenine, guanine cytosine and uracil containing
nucleotide.
3. DNA is
a double stranded helical structure while RNA is mainly a single stranded
structure except rRNA.
4. DNA is
of just one kind while RNA is of three kinds including rRNA, tRNA and mRNA
(r=ribosomal, t=transfer, m =messenger).
5. DNA molecule is always much longer than
RNA molecule.
6. DNA is generally more stable than RNA
as it is more resistant to spontaneous enzymatic breakdown.
Types
of Nucleic acids
There
are two types of nucleic acids:
1. Ribonucleic
acid (RNA)
2. Deoxyribonucleic
Acid (DNA)
Ribonucleic acid
(RNA)
Definition
Ribonucleic acid (RNA) is
one of the two major classes of nucleic acids and is
an important biological macromolecule that is present in all biological cells. It is a
single-stranded nucleic acid similar to DNA but having ribose sugar rather than
deoxyribose sugar and uracil rather than thymine as one of the pyrimidine
bases.
Function
1. The main function of RNA is cellular
protein synthesis.
2. It is
responsible for putting the genetic information to work in the cell to build
proteins. Its role is like a messenger.
Composition
The RNA molecule is composed of a pentose sugar ribose, phosphoric
acid and some cyclic nitrogenous bases.
Type of Sugar present
RNA has ribose sugar (β-D-ribose)
in it as the sugar moiety.
Nitrogenous bases present
The heterocyclic bases present in RNA
are adenine (A), guanine (G), cytosine(C) and uracil (U). In RNA, the fourth
base is different from that of DNA.
Structure and Strands
The RNA is a single stranded molecule (which
sometimes folds back; that results in a double helix structure).
Types
There are three types of RNA molecules,
each having a specific function:
(i) messenger
RNA (m-RNA)
(ii) ribosomal
RNA (r-RNA)
(iii) transfer
RNA (t-RNA)
Synthesis
and Mechanism of Action
RNA is
synthesized by DNA to transmit the genetic information.
RNA
receives, reads, decodes and uses the given information to synthesize new
proteins.
Thus
RNA is responsible for directing the synthesis of new proteins.
Deoxyribonucleic Acid (DNA)
Discovery
Its
structure was discovered by J. Watson and F. Crick in 1953.
Definition
DNA
consists of deoxyribose sugar. It is long two-chained double stranded
molecule consisting of two chains of considerable length.
Function
DNA is
the permanent storage place for genetic information in the nucleus of a cell.
It carries and stores all genetic information of the cell. It passes these
information as instructions from generation to generation how to synthesize
particular proteins from amino acids. These instructions are ‘genetic code of
life’. They determine whether an organism is a man or a tree or a donkey and
whether a cell is a nerve cell or a muscle cell.
Composition
Each
chain of DNA is made up of pentose sugar deoxyribose, phosphate and some
cyclic nitrogenous base.
Type of Sugar present
The sugar moiety
present in DNA molecules is β-D-2-deoxyribose.
Nitrogenous bases present
The heterocyclic nitrogenous
bases in them are adenine (A), guanine (G), cytosine(C) and thymine (T). These
bases and their arrangement in the molecules of DNA play an important role in
the storage of information from one generation to the next one.
The
sugar and phosphate groups make the backbone of the chains and two chains are
linked through bases. The chains are wrapped around each other in a double
helix form. DNA has a double-strand
helical structure in which the strands are complementary to each other.
Function
of Base Sequence
The
sequence of nitrogenous bases in DNA determines the protein development in new
cells.
Function
of double helix
The
function of the double helix formation of DNA is to ensure that no disorder
takes place.
Effects
of Errors in Genes
DNA
carries genes that controls the synthesis of RNA. Errors introduced into the
genes synthesize faulty RNA. It synthesizes faulty proteins that do not
function the way they are supposed to. This disorder causes genetic diseases.
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