CHEMISTRY TEXTBOOK

} Phosphate Sugar Phosphate Sugar Phosphate

base

Sugar

base

3'

Sugar-phosphate

backbone

base

5'

(a)

P S P S P S P S

B B B B

(b) 5' 3'

Fig 14.29 : Polynucleotide structure of nucleic acids :

Schematic representations (a) and (b)

Problem 14.5 : Draw a schematic representation of trinucleotide segment 'ACT' of a DNA
molecule.
Solution : In DNA molecule sugar is deoxyribose. The base 'A' in the given segment is at 5'
end while the base 'T' at the 3' end. Hence the schematic representation of the given segment of
DNA is

Phosphate deoxyribose Phosphate deoxyribose Phosphate deoxyribose

A C T

5' 3'

• 
  

N

N

NH 2

O O

OH

O-P-O-CH 2

O

O

5'

3`

(dCMP)

O

OH

N

N

N

N

NH 2

O-P-O-CH 2

O

O

5'

3'

(dAMP)

Fig 14.28 : Formation of a dinucleotide

{ O

OH

O P-O-CH 2

O

O

5'

3'

N

N

N

N

NH 2

N

N

NH 2

O-P-O-CH (^2) O O
O
O
5'
3'
Phosphodiester
linkage
5' end
3' end