RNA:

• RNA is a nucleic acid. It is composed of ribose and uracil and contains coding regions (exons) as well as noncoding regions (introns).
• There are three types of RNA – tRNA, mRNA, and rRNA. 
• RNA mediates cellular processes such as cell signaling and protein expression. 
• It is also responsible for transporting amino acids to ribosomes. 

mRNA:

• mRNA is a type of RNA
• mRNA contains only protein-coding regions (exons). It encodes for a specific amino acid sequence of a protein. 
• mRNA sequences are longer than the other two types of RNAs.