R

1. MOLECULAR BASIS OF
INHERITANCE
CHAPTER 6

2. RECAP
• NUCLEIC ACIDS-- Polymer of nucleotides
 Polynucleotide chain
• TYPES OF NUCLEIC ACIDS-
1. RNA- Ribonucleic acid
(Polymer of Ribonucleotides)
2. DNA- Deoxyribonucleic acid
(Polymer of deoxyribonucleotides)

3. 3 Components of a Nucleotide
1. Nitrogenous Base 2. Pentose Sugar
3. Phosphate
group
Purines Pyramidines
Ribose sugar
in RNA
Deoxyribose
sugar in DNA
gives negative
charge to nucleic
acids
9 member double
ring
5member single
ring
1. Adenine (A)
(both in DNA and
RNA)
1. Cytosine(C )
(both in DNA and
RNA)
2. Guanine(G)
(both in DNA and
RNA)
2. Thymine(T)
(only in DNA)
3. Uracil(U)
(only in RNA)

4. Formation of a Nucleotide
Nitrogenous base
(A,T,G,C in DNA)
(A,U,G,C in RNA)
Ribose sugar in RNA
Deoxyribose sugar in
DNA
NUCLEOSIDE
(GLYCOSIDIC
BOND/LINKAGE)
Phosphate Group
(Phospho ester
linkage/bond)
NUCLEOTIDE

6. Nucleotides of
Nucleosides of
DNA / RNA
• Deoxyadenosine / Adenosine
• Deoxyguanosine / Guanosine
• Deoxycytidine / Cytidine
• Deoxythymidine / Uridine
Purines and pyrimidines
1. Adenosine mono phosphate (AMP)/
Adenylic acid
Adenosine di phosphate (ADP)
Adenosine tri phosphate (ATP)
2. Guanosine mono phosphate (GMP)/
Guanylic acid
Guanosine di phosphate (GDP)
Guanosine tri phosphate (GTP)
3. Cytosine mono phosphate (CMP)/
Cytidylic acid
Cytosine di phosphate (CDP)
Cytosine tri phosphate (CTP)
4. Thymidine mono phosphate (TMP)/
Thymidylic acid
Thymidine di phosphate (TDP)
Thymidine tri phosphate (TTP)

7. Formation of a Dinucleotide

8. Structure of Poly Nucleotide
1. Nucleic acids i.e., DNA and RNA are polymers of
nucleotides( nucleoside mono phosphate)
2. The carbons of pentose sugars are primed as 1I, 2I,
3l to distinguish them from the carbons of
nitrogenous bases.

9. 3. Adjacent nucleotides are connected
together to form a long polymer chain
/poly nucleotide for any one nucleotide ,
the phosphate attached to the
hydroxyl group at the 5’ carbon
of pentose sugar is in turn bonded
to the hydroxyl group of 3’
carbon of pentose sugar of the next
nucleotides . Thus two nucleotides are linked through 3'-5'
phosphodiester linkage to form a dinucleotide.

10. • Since each phosphate hydroxyl bond is an ester bond ,
the linkage between two nucleotides is called 3’-5’ phosphate
diester linkage or bond. The chain of nucleic acid is
abbreviated from 5’ end to 3’ end in left to right order.
• Both glycosidic and phosphodiester bonds are formed
by condensation reactions that involve elimination of water.
• Several thousands of nucleotides are linked together to
form a polynucleotide chain.

11. • Polarity of polynucleotide chain: the polynucleotide
chain shows polarity (direction) . A polymer thus formed has
at one end a free phosphate moiety 5' -end of ribose sugar,
which is referred to as 5’-end of polynucleotide chain.
Similarly, at the other end of the polymer the ribose has a free
3' -OH group which is referred to as 3'-end of the
polynucleotide chain. The backbone in a polynucleotide chain
is formed due to sugar and phosphates. The nitrogenous
bases linked to sugar moiety project from the backbone

12. • In RNA, every nucleotide residue has an additional –OH group
present at 2' -position in the ribose.
• Also, in RNA the uracil is found at the place of thymine (5-methyl
uracil, another chemical name for thymine).

13. Structure of DNA:
• DNA as an acidic substance present in nucleus was
first identified by Friedrich Meischer in 1869.
• He named it as ‘Nuclein’.
• The structure of DNA was first worked out by James
Watson and Francis Crick in 1953.