DNA is considered to be the main source of genetic information. It is exclusively responsible for the identity of different species of organisms. DNA controls all the cellular functions.

The DNA is organised into genes, the fundamental units of genetic information. The genes control the protein synthesis through the mediation of RNA as shown below:

DNA  RNA  Protein

Besides being present in the nucleus of eukaryotic organisms, DNA is also found in the mitochondria and chloroplasts. DNA in these organisms performs specified functions with regard to protein synthesis.

1. RNA performs several functions, carried out by three different types of RNAs.
2. Messenger RNA (mRNA) specifies the sequence of amino acids in the protein synthesis (translation).
3. Ribosomal RNA (rRNA) is found in combination with proteins and is associated with the structure and function of ribosomes and factories of protein synthesis.
4. Transfer RNA (tRNA) delivers amino acids to ribosomes for protein synthesis.
5. RNA, as ribonucleoprotein, participates in the post-transcriptional modification of other RNAs.
6. RNA (not DNA) is the genetic material carrying hereditary information in many viruses.