Post Transcriptional Modification, Process and Significance

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Steps involved in post-transcriptional modification of hnRNA

The major steps involved in post-transcriptional modification include capping, tailing, and splicing.

Capping

Capping occurs at the 5' end of the hnRNA. A unique nucleotide, methyl guanosine triphosphate (mGppp), is added to the 5' end. This cap protects the RNA from degradation by exonucleases and facilitates ribosome binding during translation. Capping is the first modification to occur during RNA processing.

Tailing

At the 3' end of hnRNA, a series of adenine residues (200–300) are added, forming a poly-A tail. This process, called polyadenylation, is template-independent. The poly-A tail enhances the stability of mRNA and aids in its transport from the nucleus to the cytoplasm .

Splicing

Splicing is the most critical step in post-transcriptional modification. Introns, which are non-coding sequences, are removed from the hnRNA. The remaining exons, which are coding sequences, are joined together to form mature mRNA. This step ensures that the RNA transcript can be translated into a functional protein.

Process of Splicing

Splicing begins when the snRNPs attach to specific sequences at the 5’ and 3’ ends of introns in the hnRNA. These sequences act as signals for splicing.

• Spliceosome Formation: The snRNPs bind to the intron regions and form a spliceosome, which is a large complex that facilitates the cutting and joining process.
• Intron Removal: The spliceosome excises the introns by cutting them out at the designated sites.
• Exon Joining: After intron removal, the remaining exons are joined together by RNA ligase to form the mature mRNA.

This precise process is vital to ensure that the final mRNA contains only coding regions. Errors in splicing can lead to the production of defective proteins, which may result in diseases or cellular dysfunctions.

Significance of Post-Transcriptional Modification

Post-transcriptional modifications are essential for producing functional mRNA from hnRNA. These modifications include capping, tailing, and splicing, which ensure mRNA stability, proper transport to the cytoplasm, and accurate protein synthesis.

• mRNA Stability: The 5' cap and 3' poly-A tail protect mRNA from degradation, allowing it to persist in the cytoplasm for translation.
• mRNA Export: The modifications signal the transport of mRNA from the nucleus to the cytoplasm for protein synthesis.
• Proper Protein Synthesis: Splicing removes introns and joins exons to form a functional mRNA sequence.
• Gene Expression Regulation: These modifications regulate mRNA stability and translation, influencing protein production.

MCQs of Post Transcriptional Modification

Q1. Capping is a process in which;

1. adenylate is added at 5' end.
2. methyl guanosine triphosphate is added at 5' end.
3. adenylate is added at the 3' end.
4. methyl guanosine triphosphate is added at 3' end.

Q2. Splicing is meant to eliminate;

1. cistrons
2. mutons
3. exons
4. introns

Q3. Methyl guanosine triphosphate is added at 5' end of hnRNA in a process of;

(1) Tailing (2) Splicing (3) Capping (4) None of these

Answers of MCQs of Post Transcriptional Modification

Ans1. Methyl guanosine triphosphate is added at 5' end., Ans2. Introns, Ans3. Capping Unlock your path to success with PW's comprehensive NEET preparation resources , which include useful guidance, personalized study plans, mock tests, and PW Online NEET Coaching , which are designed to help you achieve your dream medical college.