Question

What are the functions of (i) methylated guanosine cap, (ii) poly-A “tail” in a mature on RNA?

Answer 1

a. Role of methylated guanosine cap:

During post-transcriptional modifications, a 7-methyl guanosine cap is added on the 5’ end of mRNA.

Function of methylated guanosine cap:

● This cap protects the mRNA from degradation by RNases present in the cell, thereby increasing the half life of mRNA until mRNA is translated outside the nucleus.

● It helps the mRNA for its binding with a smaller subunit of the ribosome during initiation of translation (mRNA-ribosome complexes).

● Cap is also the binding site of many proteins involved in translation. For example, this cap is identified by 18S rRNA and without it translation would not happen.




b. Role of polyA tail:

200 - 300 adenylated residues are added on the 3’end of mRNA called the polyA tail.

● Tail also protects the mRNA from degradation by RNases present in the cytoplasm of the cell.

● It also helps in movement of mRNA into the cytoplasm.