1. Ribonucleic acids are similar to DNA.

Cells contain upto eight times high quantity of RNA than DNA. RNA is found in large amount in the cytoplasm and a lesser amount in the nucleus.

2. RNA molecules are classified according to their structure and function into three major types. 

1. Ribosomal RNA (r – RNA) 

2. Messenger RNA (m – RNA) 

3. Transfer RNA (t – RNA

3. r – RNA: 

r – RNA is mainly found in cytoplasm and in ribosomes, which contain 60% RNA and 40% protein. Ribosomes are the sites at which protein synthesis takes place. 

4. t – RNA: 

t – RNA molecules have lowest molecular weight of all nucleic acids. They consist of 73 – 94 nucleotides in a single chain. The function of t – RNA is to carry amino acids to the sites of protein synthesis on ribosomes. 

5. m – RNA: 

m – RNA is present in small quantity and very short lived. They are single stranded and their synthesis take place on DNA. The synthesis m-RNA from DNA strand is called transcription. m – RNA carries genetic information from DNA to the ribosomes for protein synthesis.