DNA and RNA

DNA and RNA | Deoxyribonucleic Acid | Ribonucleic Acid – Chromosomes, Nucleotide and
Nucleoside, Nucleic acids, DNA and RNA, Recombinant DNA.

Nucleus

· Nucleus contains thread-like structures called chromosomes [long continuous
molecule of DNA]. These carry genes and help in inheritance or transfer of
characters from the parents to the offspring. The chromosomes can be seen only
when the cell divides.
· Gene is a unit of inheritance in living organisms. It controls the transfer of a
hereditary characteristic from parents to offspring.

Chromosomes
· In a cell which is not dividing, dna is present as part of chromatin material.
Chromatin material is visible as entangled mass of thread like structures.
· The nucleosome is the fundamental subunit of chromatin. Each nucleosome is
composed of a little less than two turns of DNA wrapped around a set of eight
proteins called histones.
· Whenever the cell is about to divide, the chromatin material gets organized into
chromosomes.
· Chromosomes are visible as rod-shaped structures only when the cell is about to
divide.
· Chromosomes are composed of DNA and Protein. Chromosomes contain
information for inheritance of features from parents to next generation in the form
of DNA (deoxyribo nucleic acid) molecules.
· DNA molecules contain the information necessary for constructing and organizing
cells. Functional segments of dna are called genes.

Nucleotide and Nucleoside
· Living organisms have a number of carbon compounds in which heterocyclic rings
can be found.
· When heterocyclic rings are attached to a sugar, they are called nucleosides.
· If a phosphate group is also found esterified to the sugar they are called
nucleotides.
· Nucleic acids like DNA and RNA consist of nucleotides only.
Heterocyclic Rings == A heterocyclic compound or ring structure is a cyclic compound
that has atoms of at least two different elements as members of its ring(s).
Ester == An organic compound made by replacing the hydrogen of an acid by an alkyl or
other organic group.

Nucleic Acids
· Nucleic acid is a macromolecule that is found in the acid insoluble fraction of any
living tissue.
· Together with polysaccharides and polypeptides these comprise the true
macromolecular fraction of any living tissue or cell.
· For nucleic acids, the building block is a nucleotide, i.e. nucleic acids are polymers
of nucleotides.
· Since nucleic acids are long chain polymers of nucleotides, they are also called
polynucleotides.
· The nucleotides are joined to one another in a chain by covalent bonds between the
sugar of one nucleotide and the phosphate of the next, resulting in an alternating
sugar-phosphate backbone.
· A nucleotide has three chemically distinct components. One is a heterocyclic
compound, the second is a monosaccharide and the third a phosphoric acid or
phosphate.
· The sugar found in polynucleotides is either ribose (a monosaccharide pentose) or
deoxyribose.
· The heterocyclic compounds in nucleic acids are the nitrogenous bases named
Adenine, Guanine, Uracil, Cytosine, and Thymine.

DNA and RNA
· Every generation of each and every species resembles its ancestors in many ways.
How are these characteristics transmitted from one generation to the next?
· It has been observed that nucleus of a living cell is responsible for this transmission
of inherent characters, also called heredity.
· The particles in nucleus of the cell, responsible for heredity, are called chromosomes
which are made up of proteins and another type of biomolecules called nucleic
acids.
· Nucleic acids are responsible for the transfer of characters from parents to off
springs. There are two types of nucleic acids — DNA and RNA.
· A nucleic acid containing deoxyribose is called deoxyribonucleic acid (DNA) while that
which contains ribose is called ribonucleic acid (RNA).
· Both DNA and RNA contain Adenine, Guanine and Cytosine. The fourth base is
Thymine in DNA and Uracil in RNA.
· The structure of DNA is a double strand [helix] whereas RNA is a single strand
molecule.
· Hydrogen bonds bind the nitrogenous bases of the two separate polynucleotide
strands to make double-stranded DNA.
· The DNA backbone is resistant to cleavage, and both strands of the double-stranded
structure store the same biological information. Biological information is replicated
as the two strands are separated.
· Within cells, DNA is organized into long structures called chromosomes. During cell
division these chromosomes are duplicated in the process of DNA replication,
providing each cell its own complete set of chromosomes.
· Eukaryotic organisms (animals, plants, fungi, and protists) store most of their DNA
inside the cell nucleus and some of their DNA in organelles, such as mitochondria
or chloroplasts.
· In contrast, prokaryotes (bacteria and archaea) store their DNA only in the
cytoplasm.
· DNA is the chemical basis of heredity and have the coded message for proteins to
be synthesized in the cell.
· There are three types of RNA — mRNA, rRNA and tRNA which actually carry out the
protein synthesis in the cell based on the coded message for proteins provided by
DNA.
· Ribonucleic acid (RNA) is implicated in various biological roles in coding, decoding,
regulation, and expression of genes.
· Cellular organisms use messenger RNA (mRNA) to convey genetic information that
directs synthesis of specific proteins.
· Many viruses encode their genetic information using an RNA genome. Example: HIV
virus used this technique to proliferate within human body.

Biological Functions of Nucleic Acids – DNA and RNA

· DNA is the chemical basis of heredity and may be regarded as the reserve of genetic
information.
· DNA is exclusively responsible for maintaining the identity of different species of
organisms over millions of years.
· A DNA molecule is capable of self-duplication during cell division and identical DNA
strands are transferred to daughter cells.
· Another important function of nucleic acids is the protein synthesis in the cell.
Actually, the proteins are synthesized by various RNA molecules in the cell but the
message for the synthesis of a particular protein is present in DNA.

DNA Fingerprinting
· It is known that every individual has unique fingerprints. These occur at the tips of
the fingers and have been used for identification for a long time but these can be
altered by surgery.
· 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.
· DNA fingerprinting is now used (i) in forensic laboratories for identification of
criminals. (ii) to determine paternity of an individual. (iii) to identify the dead bodies
in any accident by comparing the DNA’s of parents or children. (iv) to identify racial
groups to rewrite biological evolution.

Recombinant DNA
· Recombinant DNA (rDNA) molecules are DNA molecules formed by laboratory
methods of genetic recombination (such as molecular cloning) to bring together
genetic material from multiple sources, creating sequences that would not otherwise
be found in the genome.
· Recombinant DNA is possible because DNA molecules from all organisms share the
same chemical structure. They differ only in the nucleotide sequence within that
identical overall structure.
· In most cases, organisms containing recombinant DNA have apparently normal
phenotypes. That is, their appearance, behavior and metabolism are usually
unchanged.

Applications of recombinant DNA technology

· Recombinant DNA is widely used in biotechnology, medicine and research.
· Recombinant DNA is used to identify, map and sequence genes, and to determine
their function.
Recombinant DNA is used to produce
· Recombinant human insulin,
· Recombinant human growth hormone,
· Recombinant blood clotting factor VIII,
· Recombinant hepatitis B vaccine,
· Insect-resistant crops etc.

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