There are three different types of RNA.
Messenger RNA or m-RNA: This is called as messenger RNA because it carries information for protein synthesis from DNA to the ribosomes in the cytoplasm. The information is carried by the m-RNA in the form of triplets called Codons. Each codon specifying an amino acid. The molecular weight of m-RNA is about 5,00,000. It constitutes about 3-5% of the total RNA.
Ribosomal RNA or r-RNA: It is called as ribosomal RNA because it is present in the ribosomes in the cell cytoplasm (site of protein synthesis). The r-RNA is highly twisted and folded upon itself. Its molecular weight ranges from 40,000 to over a million. It forms about 80% of the total RNA.
Transfer RNA or t-RNA: The t-RNA strand is about 70-90 nucleotides long and folded upon itself. It is also known as soluble RNA (s-RNA). It is the smallest amongst the three types of RNA. The t-RNA carries the required specific amino acid from the cell cytoplasm to the ribosome which is the site of protein synthesis. The molecular weight of t-RNA ranges from 23,000 to 30,000. It forms about 10-20% of the total RNA of the cell.