Nucleic acids such as DNA and RNA are essential biological molecules found in the nuclei of living cells. DNA controls cellular functions and heredity by carrying the genetic instructions in its double-stranded structure. DNA is made up of nucleotides containing deoxyribose, phosphate groups, and organic bases (adenine, guanine, cytosine, thymine) that bond together in a double helix with base pairing between adenine-thymine and cytosine-guanine. RNA also carries out important cellular functions and exists in different types including mRNA, tRNA, and rRNA.

1. 1

2. NUCLEIC ACIDS:
• Are biological molecules essential for known forms of life
on earth
• They include DNA and RNA
• Discovered by Friedrich Miescher in 1869
• They are named so because of their initial discovery in
nucleus

3. DNA stands for deoxyribo nucleic acid
This chemical substance is present in the nucleus
of all cells in all living organisms
DNA controls all the chemical changes which
take place in cells
The kind of cell which is formed, (muscle, blood,
nerve etc) is controlled by DNA
The kind of organism which is produced (buttercup,
giraffe, herring, human etc) is controlled by DNA
DNA 2

4. DNA is a very large molecule made up of a long
chain of sub-units
The sub-units are called nucleotides
Each nucleotide is made up of
a sugar called deoxyribose
a phosphate group -PO4 and
an organic base
DNA molecule 3

5. The deoxyribose, the phosphate and one of the bases
adenine
deoxyribose
PO4
Combine to form a nucleotide
NUCLEOTIDES
6

6. The most common organic bases are
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
THE BASES
5

7. The bases always pair up in the same way
Adenine forms a bond with Thymine
and Cytosine bonds with Guanine
Bonding 1 10
Adenine Thymine
Cytosine Guanine

8. • Adenine and guanine are known as
PURINES
• Thymine and cytosine are known as
PYRIMIDINES, in RNA instead of thymine
it is Uracil
• Adenine pairs with Thymine forming two
hydrogen bonds
• Cytosine pairs with Guanine forming with
three hydrogen bonds

9. Purines Pyrimidines
Purines are double ringed structures Pyrimidines are single ringed
structures
Example of purine bases are
Adenine and Guanine
Example of pyrimidine bases are
Thymine and Cytosine( in DNA),
Uracil and cytosine ( in RNA)

10. Ribose is a sugar, like glucose, but with only five
carbon atoms in its molecule
Deoxyribose is almost the same but lacks one
oxygen atom
Both molecules may be represented by the symbol
THE SUGARS:RIBOSE & DEOXYRIBOSE
4

11. STRUCTURE OF DEOXYRIBONUCLEOTIDE
AND RIBONUCLEOTIDE

12. NUCLEOSIDE NUCLEOTIDE
Nucleoside is a component formed by
the union of a nitrogen base with a
pentose sugar
Nucleotide is a component formed
by the union of a nitrogen base, a
pentose sugar and phosphate
It is a component of nucleotide It formed after phosphorylation of
nucleoside

13. FUNCTIONS OF DNA:
• It is the genetic material, therefore responsible for carrying
all the hereditary information.
• It has property of replication essential for passing genetic
information from one cell to its daughters or from one
generation to next.
• Crossing over produces recombination
• Changes in sequence and no. of nucleotides causes
Mutation which is responsible for all variations and
formation of new species.
• It controls all the metabolic reaction of cells through RNAs
and RNA directed synthesis of proteins.

14. A molecule of
DNA is formed
by millions of
nucleotides
joined together
in a long chain
PO4
PO4
PO4
PO4
sugar-phosphate
backbone
+ bases
Joined nucleotides 7

15. In fact, the DNA usually consists of a double
strand of nucleotides
The sugar-phosphate chains are on the outside
and the strands are held together by chemical
bonds between the bases
8

16. PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
2-stranded DNA 9

17. PO4
PO4
PO4
thymine
PO4
PO4
PO4
PO4
adenine
cytosine
PO4
guanine
Bonding 2 11

18. PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
Pairing up 12

19. ROLE OF PHOSPHODIESTER
LINKAGE
• Phosphodiester Bonds Link
Successive Nucleotides in Nucleic
Acids
• The successive nucleotides of both
DNA and RNA are covalently
linked through phosphate-group
“bridges,” in which the 5’-
phosphate group of one nucleotide
unit is joined to the 3-hydroxyl
group of the next nucleotide,
creating a phosphodiester linkage .

20. The chain has a 5 end,
which is usually attached
to a phosphate, and a 3
end, which is usually a
free hydroxyl group

21. The paired strands are coiled into a spiral called
A DOUBLE HELIX
13

22. sugar-phosphate
chain
bases
THE DOUBLE
HELIX
14

23. ANTIPARALLEL NATURE
• The two strands of DNA are also antiparallel(run
in opposite directions) to one another.
• A strand of DNA can have the direction 5'-3' or 3'-
5'.
• One strand in the DNA molecule is 5'-3' and the
other strand is 3'-5'.

24. DNA STRUCTURE

25. • The two strands run antiparallely and are complimentary to each
other.
• The coiling is right handed.
• The major groove occurs where the backbones are far apart, the
minor groove occurs where they are close together.
• Two helical polynucleotide chains are coiled around a common
axis. The chains run in opposite directions.
• The sugar-phosphate backbones are on the outside and, therefore,
the purine and pyrimidine bases lie on the inside of the
helix.Adenine always pairs with Thymine, Guanine binds with
Cytosine
• The bases are nearly perpendicular to the helix axis, and adjacent
bases are separated by 3.4 Å.
• The helical structure repeats every 34 Å, so there are 10 bases (= 34
Å per repeat/3.4 Å per base) per turn of helix.
• There is a rotation of 36 degrees per base (360 degrees per full
turn/10 bases per turn).
• The diameter of the helix is 20 Å.

27. CHARGAFFS RULE:
• “It states that DNA from any cell of all organisms should
have a 1:1 ratio of pyrimidine and purine bases and more
specifically that the amount of guanine is equal to amount
of cytosine and amount of adenine is equal to amount of
thymine”
• %A=%T
• %G=%C

28. DENATURATION OR MELTING
• The hydrogen bonds between the nitrogenous bases of
complementray DNA can break due to high temperature,
low or high pH known as Melting or Denaturation of
DNA.
• A-T base pairs can go easy denaturation due to presence
of only two hydrogen bonds, whereas G-C base pairs are
comparitively more stable (high melting point) due to
presence of three hydrogen bonds.

29. RNA
• Like DNA, RNA is also made of a long chain of
nucleotides.
• Some RNA molecules play an active role in cells by
catalyzing biological reactions, controlling gene
expression, or sensing and communicating responses to
cellular signals.
• In RNA molecules instead of the base T, base U is found.
• Generally three types of RNA molecules are found in the
cell – mRNA, rRNA, and tRNA.

30. MESSENGER RNA:mRNA
• Comprise only 5% of total cellular RNA.
• Messenger RNA (mRNA) carries information about a protein
sequence to the ribosomes, the protein synthesis factories in
the cell.
• It is coded so that every three nucleotides (a codon)
correspond to one amino acid.
• The synthesis of mRNA takes place inside the nucleus and
after its synthesis, it is exported out where it attaches to
ribosomes for protein synthesis.
• After certain amount of time the message in mRNA is
degraded into its component nucleotides.

31. TRANSFER RNA:tRNA
• tRNA represents 15% of total RNA in the cell.
• Transfer RNA (tRNA) is a small RNA chain of about 80
nucleotides that transfers a specific amino acid to a growing
polypeptide chain at the ribosomal site of protein synthesis
during translation.
• It has sites for amino acid attachment and an anticodon region
for codon recognition that binds to a specific sequence on the
messenger RNA chain through hydrogen bonding.

32. STRUCTURE OF tRNA
• Anticodon arm :
• Made up of three nitrogen bases for
recognising and attaching to the
codon of mRNA
• A-A Binding Site:
It lies at the3’ end and has CCA-OH
group
• TΨC Loop:
Contains pseudouridine, site for
attaching the ribosomes
• DHU Loop:
Contains dihydrouridine, binding site
for aminoacyl synthetase enzyme.
• Variable loop:
Lies between the anticodon and TΨC
loop.

34. RIBOSOMAL RNA (rRNA):
• 80% of total RNA in the cells are rRNA
• Ribosomal RNA is a constituent of
Ribosomes
• rRNA are found in combination with
several proteins (about 82 proteins) as
component of the ribosome which is the site
of protein synthesis.

35. CENTRAL DOGMA
• The set of ideas that describes how the cell uses the information
stored in DNA is called the Central dogma
• The first step of central dogma is Transcription
• Transcription uses DNA as a template to copy genetic information
into form of RNA
• The second step of central dogma is Translation
• Translation synthesizes the protein using RNA as a template

36. Character RNA DNA
Nitrogenous bases RNA contains adenine,
uracil, cytosine, and
guanine.
DNA contain adenine,
thymine, cytosine,
guanine;
Strandedness RNA is single-stranded. DNA is double-stranded
Location RNA can be found in both
the nucleus and
cytoplasm.
DNA is only found in the
nucleus
Functions RNA carries out protein
synthesis.
RNA transfers the
information to other
places in the cell
DNA contains the
information for protein
synthesis.
DNA stores genetic
information
Pentose sugar Hydroxyl group present at
2 carbon of the pentose
sugar
Absence of hydroxyl
group at 2 C of the
pentose sugar