Nucleic acid and chromosomes


what are Nucleic acid and chromosomes? what are the uses of Nucleic acid and chromosomes? types of Nucleic acid and chromosomes?

Nucleic acid and chromosomes:-

Chemical structure based composition of nucleic acid :-

Chemical structure based composition of nucleic acidNucleic acid is a long polymeric molecule, comprising of numerous monomers called nucleotides.

Nucleotides is made up of three component-sugar, nitrogen base, phosphoric acid

In dna, pentose sugar is deoxyribose, while in RNA it is ribose.

The four nitrogen bases found in dna are adinine, guanine, thymine  and cytosine.

 rna contains uracil instead of thymine.

The nitrogenous bases adenine and guanine double ring structures call purines, while thymine and cytosine are single ring called pyrimidine.

Structure of DNA:-

DNA is a polymer of de-oxy ribose nucleotide. It is composed of d-amp, d-gmp, d-cmp, d-tmp.

Watson and crick model of dna structure:-

The double helical structure of dna was proposed by james watson and francis crick in 1953.

They got nobel prize in 1962.

The structure of dna double helix is comparable to twisted ladder.

The salient features of this model of dna are given below as:-

The dna is a right handed double helix.

It consists of two de-oxy ribose nucleotide chains twisted each other on a common axis.

The two strands are antiparallel that have one stand runs in 5’ to 3’ and other strand runs 3’ to 5’ direction.

The width {or} diameter of a double helix is 20a0.

Each turn of helix is 34 a0 units with 10 pairs of nucleotides each pair placed at a distance of about 3.4 a0 units.

The two polynucleotide chains are not identical complementary due to base pairing.

The two stands are held together by hydrogen bonds formed by complementary base pair.

A=p has two hydrogen bonds where as the g=c pair has three hydrogen bonds.

 the hydrogen bonds are formed between a purine and pyrimidine only.

The complementary base pair in dna helix prover chargaffs  rule.

The content of adenine, equal to that of thymine and guanine equal to that of cytosine.

Genetic information on one of the 2 stands known as template strand {or} sense strand.

The opposite stand is antisense strand.

cytosine and guanine

The double helix has major grooves  and minor grooves  along phosphodiester backbone.

Types of DNA:-

That double helical structure of dna exist in atleast 6 different forms a,b and z among these a,b,z forms are important.

The b form of dna double helix described by watson and crick.

Each turn of the b-forms has 10 base pair.

The a form is also right handed helix. It contain 11 base pairs.

The z form is a left handed helix it contains 12 base pairs per turn. 

Hydrogen bonds:-

A great deal of information is obtained by observers of tm with base composition and experimental condition.

The value of tm form many dna molecules are plotted versus percentage g+c.

tm with increasing percentage g+ c.

This fact is interrupted in term of the relative number of hydrogen bonds in a g-c pair and a-t pair{2}.

Higher temperature is required to distribute g-c pair than a a-t pair because double standard structure is stabilize atleast in part by hydrogen bonds.

Hydrophobic interaction in dna:-

The reagent that would the enhance the interaction of weekly soluble substance with water are good disrupt the water shell about the substance should weaken hydrophobic interaction.


Methanol increases the solubility of bases.

The salt sodium trifluoro acetate is an example of the second type.

The addition of both these reagents reduces. Tm anoumously which suggest that hydrophobic interactions are also important in stabilizing the dna structure.

Low solubility of substance favours hydrophobic clusters.

Base stacking is eliminated by the addition of reagents that weaken hydrophobic interactions.

If a dna sample is heated, base stacking is reduced, during the same transition, in which a260 nanometers increases.

Reagents that break down hydrogen bonding have no effect on the base stacking of single standard polynucleotides. But reduce base stacking of double stranded dna to the degree found in the denatured dna.

These result to lead to the conclusion that the base of double stranded dna are more stacked than those in ss dna.

The increased stacking in ds dna can be accounted for by considering the effect of hydrogen bonds between two stands on the structure of each of the individuals stands.

Both hydrogen and hydrophobic interactions are weak and easily disputed by thermal motion.

Maximum hydrogen bonding is achieved when all bases are pointing in the right direction similarly stacking is enhanced, it is bases for unable to twilt {or} swing out from the stacked array.

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