Question

Prokaryotic mRNA can be (A) . The coding regions of eukaryotic mRNA can be (B) . In addition to these differences, eukaryotic mRNA is chemically modified at (C) .

A choices = monocistronic, polycistronic, monocistronic or polycistronic, bicistronic

B choices = continuous or interupted, interrupted, continuous

C choices = the 3' end, the 5' end, the 5' and 3' end

Answer 1

Answer: Prokaryotic mRNA can be monocistronic or polycistronic.

The coding regions of eukaryotic mRNA can be interrupted

eukaryotic mRNA is chemically modified at the 5' and 3' end

Explanation: Cistron is a nucleotide sequence on the chromosome responsible for synthesis of a polypeptide. Monocistronic genes produce a single type of polypeptide while a polycistronic gene is a group of genes which are synthesizing related polypeptides. On a polycistronic gene the RNA polymerase will synthesize a single RNA transcript but which has message for different polypeptides and the ribosomes will be able to make different polypeptides from a single RNA molecule.

The eukaryotic mRNA, synthesized by the process of transcription in the nucleus has the coding regions and the non-coding regions, called as exons and the introns respectively. The coding region of the pre-mRNA is interrupted.The exons are the coding part while the introns are the non coding regions which needs to be removed before the polypeptide is synthesized (translation). The introns are removed by the process of splicing this is also known as post-transcriptional modification of the mRNA molecule.

In the process of post-trascriptional modification the pre-RNA undergoes 3 changes 1) at 5’ end of the pre-mRNA 7-methylguanosine is added, this is known as capping

2) there is addition of polyadenylated sequence at the 3’end, this is known as tailing

3) the non-coding regions or introns are removed with the help of spliceosomes.

The process of capping and tailing protects the mRNA when it moves to cytoplasm for translation and helps in transportation of mRNA to ribosome.