Question

There are several changes that occur to pre-mRNA in eukaryotic cells to produce the final mRNA molecule that will be used in translation. This process is called RNA processing. Which of the following occurs in the process of producing this final mRNA molecule? a poly-A tail is added to the 5' end a modified guanine nucleotide is added to the 3' end the introns are cut out and the exons are attached to each other none of the above

Answer 1

• During the processing of pre-mRNA or during Post transcriptional modification in eukaryotic cell, the introns are cut out and the exons are attached to each other. According to the given question, this statement is true about the processing of pre-mRNA.

a) The first statement is false. During pre-mRNA processing, poly-A tail is added to the 3' end, soon after transcription. This tailing process is called polyadenylation. As many as 200 or more adenine nucleotides are added to the 3' end of the pre-mRNA with the help of the enzyme Adenylic acid transferase.

b) The second statement is false. During post transcriptional modification or during the processing of pre-mRNA to final mRNA, modified guanine nucleotide is added is added to the 5' end. This process is called "capping". It is the formation of a protective 'cap' at the 5' end of the pre-mRNA by the addition of 7-methyl guanosine.

c) The third statement is true. During RNA processing, The introns (non-coding regions) are cut out and the exons (coding regions) are attached to each other. This process is called "splicing". Splicing is essentially the removal of the non-coding regions (introns) and the subsequent ligation of the coding regions (exons) of mRNA. The introns are sliced away by ribonucleases. The remaining exons are soon joined together by the enzyme RNA ligase.