Nucleic acid

Nucleic acid.

The complex compound found in living beings which are responsible for the transmission of heredity character and proteins synthesis are called nucleic acid.

Nucleic acid constitutes an important class of biomolecule which are found in all living cells except the red blood cells of the mammal. They are present in the cells in the form of nucleoproteins ( the proteins containing nucleic acid as non-proteinous part). They are the major constituent of a nucleic acid of all the cells. There are two types of nucleic acid They are

1. Ribonucleic acid RNA.
2. Deoxyribonucleic acid DNA.

The structure of Nucleic acid.Both DNA and RNA are the polymers of nucleotides. The nucleic acid is made up of three constituent. They are

1. pentose sugar,
2. Nitrogen bases and
3. Phosphate group.

1. Pentose sugar.

The five-carbon monosaccharide I,e pentose sugar are found in a nucleic acid. These two sugar are obtained by hydrolysis of nucleic acid. They are ribose and deoxyribose. Ribose and deoxyribose differ in the structure at C2. Deoxyribose has one oxygen less at C2 compare to ribose.

2. Nitrogen base.

The nitrogen bases are found in nucleotide are aromatic heterocyclic compound. The nitrogen bases are of two types. They are.

1. Purine and.
2. Pyrimidines.

a. Purine.

The commonly found purines are adenine (A) and guanine (G).

b. Pyrimidines.

The commonly found pyrimidines are thymine (T), Cytosine and Uracil (U) etc.

3. Phosphate group.

Phospho or nucleic acid had the binding of H₃PO₄ as a phosphate group.

The structural difference between DNA and RNA.

Although DNA and RNA are the polynucleotides, yet there can be the limitless possible structure for this molecule because of the ample combination of various nucleotides. In general, DNA is deoxyribose sugar and RNA are ribose sugar. The nitrogen bases present in DNA are Adenine , guanine, uracil and cytosine. But ribose sugar has Adenine guanine, thymine and cytosine. In the DNA and RNA thymine base is replaced by uracil.

Difference between DNA and RNA

Deoxy Ribose Sugar.

James Watson and Francis Crick (1953) proposed that DNA molecule consists of two polynucleotide chains coiled together in the form of a double helix. The two chains of the double helix are held together by hydrogen bonds especially between a purine and a pyrimidine base pair. A is linked with T with two hydrogen bonds and a G is linked to C with three hydrogen bonds. The two chains are said to be complementary to each other since the base sequence of one strand automatically fixes that of the other due to the above base pairing principle. The double helix structure of DNA is regarded as one of the most significance contributions of science in recent times.

Ribose nucleic acid.

RNA is found in the nucleus and in the cytoplasm. It is a single-stranded, long chain macromolecules of the ribonucleotide. Like DNA the ribonucleotide of RNA is also formed by cross-linking of three substance. Sugar, Nitrogen bases and phosphate. The ribose sugar differs from the deoxyribose sugar of DNA in having four rather than three hydroxyl group. The nitrogenous bases of RNA are of two types.

1. Purine: Adenine (A) and guanine (G).
2. Pyrimidine; Cytosine (C) and (Uracil).

Thus structurally DNA and RNA show two main differences.

1. DNA contains deoxyribose sugar and RnA contains ribose sugar.
2. DNA contains thymine and RnA contain uracil.

Being single stranded, the nitrogen bases of RnA remains unpaired and the complementary bases are found in the same strand. The four nucleotides in the RNA are A, G, C, and U nucleotides. Double stranded RNA is found in reovirus. In a double stranded RNA, base pairing occurs between purine and pyrimidines. Guanine and cytosine are held together by three hydrogen bonds and uracil and adenine are held together by two hydrogen bonds.

Hence, a nitrogen base, ribose sugar and a phosphate form a nucleotide and a nucleotide without the phosphate are called nucleoside.

The RnA is mainly classified into three types.

1. m-RNA (Messenger RNA).
2. r-RNA (Ribosomal RNA).
3. t-RNA(Transfer RNA).

The biological function of Nucleic acid.

One of the amazing aspects of the living organism is to reproduce themselves. Reproduction of cell is basically the self-duplication of a cell by division. A cell must have a record of an amino acid sequence of all its enzymes and proteins because they are constantly required for the production of new cells and repair of the damaged cells. The difference in various species also results from the content of their constituent proteins. At the time of divisions of the cells, the new cells must be provided with the identical information about their proteins. Nucleic acids play a significant role in this process. The molecular structure of nucleic acid store this information in the coded form. Such stored information is known to control the inherited characteristics of the next generations as well as many of the ongoing life process of the living organisms.

The function of nucleic acids.

1. DNA is responsible for transmission of the hereditary character.
2. RNA is responsible for protein synthesis.

Reference

Bahl, B S, Bahl, and Arun. Advanced Organic chemistry. S. Chand and company Ltd., n.d.

Sthapit, M K, R R Pradhananga, and K B Bajracharya. Foundations of chemistry. Taleju Prakashan, n.d.

Tewari, K S, S N Mehrotra, and N K Vishnoi. A textbook of organic chemistry. Vikash publishing House Pvt. ltd., n.d.

Verma, N K and S K Khanna. Compressive chemistry. 8th edition. Laxmi publications P. Ltd., 1999.