Index >>Ribose Nucleic Acids >>Structure of Messenger RNA - mRNA

Structure of Messenger RNA - mRNA - Messenger RNA is always single stranded. It contains mostly the bases adenine, guanine, cytosine and uracil. There are few unusual substituted bases. Although there is a certain amount of random coiling in extracted mRNA, there is no base pairing. In fact base pairing in the mRNA strand destroys its biological activity.

Since mRNA is transcribed on DNA (genes), its base sequence is complementary to that of the segment of DNA on which it is transcribed. This has been demonstrated by hybridization experiments in which artificial RNA­DNA double strands are produced. Hydrization takes place only if the DNA and RNA strands are complementary.

1. Cap. At the 5' end of the mRNA molecule in most eukaryote cells and animal virus molecules is found a 'cap'. This is blocked methylated structure, m7Gpp Nmp Np or m7Gpp Nmp Nmp Np. where: N = any of the four nucleotides and Nmp = 20 methyl ribose. The rate of protein synthesis depends upon the presence of the cap. Without the cap mRNA molecules bind very poorly to the ribosomes.

2. Noncoding region 1 (NC1). The cap is followed by a region of 10 to 100 nucleotides. This region is rich in A and U residues, and does not translate protein.

3. The initiation codon is A UG in both prokaryotes and eukaryotes.

4. The coding region consists of about 1,500 nucleotides on the average and translates protein.