• These are biomolecules which consist of one or two
ring of nitrogenous base, either purine or
pyrimidine derivatives, a five carbon sugar (pentose
sugar) and one or more phosphate groups
Myths of DNA
Fibonacci sequences – 0,1,1,2,3,5,8,13.21,34,55,89….
Φ = 1.61803
• Nucleic acids are polymers of nucleotides that occurring
in all living systems
• Nucleic acids are the chemical carriers of an organism’s
genetic information which play a great role functions in
a living system
• Store and transmit genetic information
• Translation of genetic information
• Nucleotide participates in almost all biochemical
processes and is the one of the most important
metabolites of the cell
Understanding Nucleic Acids
•Nucleic acids are the chemical carriers of an organism’s
genetic information (DNA & RNA)
•Nucleic acids are polymers of nucleotides
•They store, transmit and translation of genetic information
•Composed with Sugar, base and Phosphate group
Nucleotides and Nucleoside
• Building blocks of nucleic acids
- Sugar + Base = Nucleoside
- Nucleoside + Phosphate = Nucleotide
▲ Nucleotides are monophosphate esters of nucleosides
Structure of nucleic acid
Nucleic Acid has 3 components:
(i) Pentose sugar (ii) Nitrogenous base & (iii) Phosphate group
(i) Pentose sugar
(ii) Nitrogenous base
Either from purine or pyrimidine derivatives
- Purine: Adenine (A) and Guanine (G)
- Pyrimidine : Thymine (T), Cytosine (C) & Urasil (U)
(iii) Phosphate group
• The most common site of phosphorylation of nucleotides
found in cells is the hydroxyl group attached to the 5'-
carbon of the ribose.
• There two types of polynucleotides: DNA and RNA
• Deoxyribose-containing nucleotide, deoxyribonucleotides,
are the monomers of DNA and
• Ribose-containing nucleotides, ribonucleotides, are the
monomers of RNA
• Common representation of the primary structure of DNA or
RNA molecules is to write the nucleotide sequences from left to
right synonymous with the 5' -----> 3' direction
• Known as Sugar-phosphate backbone
Condensation commonly occurs between 5'-phosphate of one
nucleotide and 3'-hydroxyl of a second (Phosphodiester bond)
(i) Deoxyribose Nucleic Acid (DNA)
• DNA contains two polynucleotide strands wound
around each other and form helical structure
• The backbone of each consists of alternating
deoxyribose and phosphate groups bonded to the 5'
carbon atom of one deoxyribose is covalently
bonded to the 3' carbon of the next
• The backbone of sugar phoshate of each strand is on
the outside of the double helix, whereas the purine
and pyrimidine bases are inside
• The two strands are "antiparallel"; that is, one strand
runs 5′ to 3′ while the other runs 3′ to 5′.
• Purine or Pyrimidine attached to each deoxyribose
projects in toward the axis of the helix
• The most important aspect of the DNA double helix
is the specificity of the pairing of bases.
DNA replication or duplication
• DNA replication is the process by which a replica or
identical copy of DNA are made in the cells
• Cells do not live forever, they must pass their genetic
information on to new cells
• It is also required that fragments of DNA (genes) have
to be copied to code for particular bodily function
• It is essential that the replication of it is EXACT
• In order for replication to occur, the following must
ｷ The actual DNA to act as an exact template
ｷ A pool of relevant and freely available
ｷ Supply of the relevant enzymes to stimulate
ｷ ATP to provide energy for these reactions
• During replication of DNA, the two strands of a
double helix unwind and separate.
• Each parent strand act as a template for the
formation of a new complementary strand.
(ii) Ribonucleic acid (RNA)
• RNA is a long unbranched macromolecule consisting of
nucleotides joined by 3' - 5' phosphoester bonds.
• RNA are responsible for putting the genetic information
to use in protein synthesis.
• Unlike DNA, RNA molecules have single strands; it does
not have complementary base ratios and the sugar unit
in RNA is a ribose rather than dioxyribose.
• One of the four bases in RNA is Uracil (U) instead of
• Uracil like thymine form a base pair with Adenine (A).
There three types of RNA
(a) Messenger RNA – (mRNA)
(b) Ribosomal RNA (rRNA) and
(c)Transfer RNA (tRNA)
(a) Messenger RNA (mRNA)
• Account for 5 – 10% of the cell RNA. This is a single-
stranded molecule formed on a single strand of
DNA by the process known as transcription.
• In the formation of mRNA only one strand of the
DNA molecule is copied i.e. the base sequence is
complementary to that of its DNA template.
• mRNA act as the template for protein synthesis
and it carries genetic information from DNA for the
AAs sequences of the protein to be synthesized.
(b) Ribosomal RNA (rRNA)
• These are found in cell ribosomes and accounts for
75 – 80% of cell RNA.
• It is synthesized by genes present on the DNA.
• The base sequence of rRNA is similar in all
organisms from bacteria to higher plants and
• Ribosomes are the sites of protein synthesis. Here
the mRNA code is translated into a sequence of
amino acids in a polypeptide chain.
(c)Transfer RNA (tRNA)
• These account for 10 – 15% of the cell RNA.
• tRNA transfer amino acids present in cytoplasm to
• Acts as an intermediate molecule between the
triplet code of mRNA and the amino acid sequence
of the polypeptide chain.
• They are carriers of activated amino acids during