Deoxy ribonucleic Acid and RNA


Deoxyribonucleic acid (DNA) is a nucleic acid that carries the genetic information to the offspring of an organism. DNA forms the chemical basis of hereditary characters. It contains the instruction for the synthesis of proteins in the ribosomes. Gene is a part of a DNA molecule.

The DNA present in the nucleus is responsible for the formation of RNA. RNA regulates the synthesis of proteins by ribosomes. DNA in mitochondria is called non-chromosomal DNA.

Structure of DNA-

DNA is a double­stranded complex nucleic acid. It is formed by deoxyribose, phosphoric acid and four types of bases. Each DNA molecule consists of two polynucleotide chains, which are twisted around one another in the form of a double helix. The two chains are formed by the sugar deoxyribose and phosphate.

 Each nucleotide is formed by-

  1. Deoxyribose – sugar
  2. Phosphate
  3. One of the following organic (nitrogenous) bases:

Purines – Adenine (A) – Guanine (G)

 Pyrimidines –Thymine (T) – Cytosine (C)

The adenine of one strand binds specifically with thymine of opposite strand. Similarly, the cytosine of one strand binds with guanine of the other strand.

DNA forms the component of chromosomes, which carries the hereditary information. The hereditary information that is encoded in DNA is called genome.

Structure of RNA –

Each RNA molecule consists of a single strand of polynucleotide unlike the double­stranded DNA. Each nucleotide in RNA is formed by:

  1. Ribose – sugar.
  2. Phosphate.
  3. One of the following organic bases:

Purines – Adenine (A) – Guanine (G)

Pyrimidines – Uracil (U)   – Cytosine (C).

 Uracil replaces the thymine of DNA and it has similar structure of thymine.

Type of RNA  -

RNA is of three types. Each type of RNA plays a specific role in protein synthesis.

1. Messenger RNA (mRNA) –

Messenger RNA carries the genetic code of the amino acid sequence for synthesis of protein from the DNA to the cytoplasm.

2. Transfer RNA (tRNA) –

Transfer RNA is responsible for decoding the genetic message present in mRNA.

3. Ribosomal RNA (rRNA)-

 Ribosomal RNA is present within the ribosome and forms a part of the structure of ribosome. It is responsible for the assembly of protein from amino acids in the ribosome.