Chemical and Physical Properties of Nucleic Acid (2018)

Properties of Nucleic Acid

A complex organic substance present in living cells especially DNA or RNA. Whose molecule consists of many nucleotides linked in a long chain.

DNA or RNA are linear molecules but sometimes in circular form.

Before we start this, you must read this: History of DNA As Heredity Material —– Degradation of Proteins (2018) – Faisal Biochemist


The nucleotide is made up of Sugar, Phosphate and Nitrogenous base. And Compound consists of a nitrogenous base linked to a sugar is called nucleoside e.g. Adenosine.


Nucleotide subunit of DNA contain a pentose {Five carbon sugar} called ribose. Nucleotide subunit of DNA contain the sugar the oxyribose. The sugar differs only in the presence or absence of an oxygen in 2prime position.

Ribose and Deoxyribose

Primer are used in the numbering of ring position in the sugar to differentiate them from in the ring position of base.

Nitrogenous Bases:

Bases are a nitrogen-containing molecule having the chemical the properties of the base. Two of the base Adenine (A) and Guanine (G) have double carbon-nitrogen ring structure are called purines.

Adenine and Guanine

The other three bases thymine(T) cytosine (C) and uracil (U) have a single ring structure and are called pyrimidine.

Thymine is fixed in DNA only, uracil is specific for RNA.

cytosine and thymine

Phosphate Functional Group:

Phosphate functional group gives DNA and RNA the properly of an Acid. The linking bond that are formed from phosphate are ester that has the additional property of being stable.

  • Normal polymerization involves addition or Nucleotide at 3’, polymerization always occur from 5’ – 3’.
  • Two two ends are designated by symbols 5’ and 3’.
  • The symbol 5’ refers to the carbon is sugar to which a phosphate group is attached and 3’ refer to carbon to which OH is attached.
  • 5’ end because no further nucleoside is attached at this end.
  • 3’ end because 3’ carbon is not further linked.
  • Phosphate gives negative to whole DNA molecule.

Chargaff Model:

In 1950, Chargaff determines the percentage amount of various bases in different organisms.

He sees that structure is always same no matter from where is DNA is extracted, The amount of Adenine is always equal to Thymine And amount of Cytosine is always equal to Guanine Total of the content of Purine is equal to a pyrimidine.

A+G     =      T+C                                C ≠ T                     C ≠ A

Purine =     Pyrimidine’s                 G ≠ T                    G≠ A


The two physic Franklin and Wilkins, trying to studies X-Ray diffraction. X-ray pass through the medium, the light is Scattered image form which is used by Scientists. And result Screen determines the shape of material.

X-ray pattern which they get is so regular, so the dimension of the helix must also be consistent.

e.g Diameters of helix stays same..

Horizontal bars correspond to helical turns Vertical distance between bars is 34 Å  which a measure of the height of one turn.

Frankline x-ray

DNA from different source have the same angle, conclude that structure of DNA is same in all species.


IN 1952, the two biologists discover DNA structure added by Franklin work,

DNA is double helical structure in which phosphate groups were on outside because they are polar and hydrophilic and bases are present on the inner side because they are non-polar and hydrophobic.

On Strand going from 5’-3’ and the other in  3’-5’ direction.

Two strand from helix and the distance from one the next one is 34 Å . both of them got noble Prize.

DNA double helix structure

Please Read the Previous Article about History of DNA. Must Comment and Share this article.

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