Which one of the following involves RNA Editing?
1. deletion, insertion or chemical modification of nucleotides that are present in the mRNA
2. joining of exons from one pre-mRNA molecule to form mRNA
3. deletion, insertion or chemical modification of nucleotides in the gene encoding the mRNA
4. joining of exons from two different pre-mRNA molecules to form mRNA

 What is RNA Editing?

RNA editing is a post-transcriptional modification process where the nucleotide sequence of an RNA molecule is altered after it has been transcribed from DNA. Unlike splicing or capping, RNA editing directly changes the RNA sequence, resulting in an mRNA that differs from its original DNA template.

 Types of RNA Editing

1. Insertion of new nucleotides

2. Deletion of existing nucleotides

3. Chemical modifications, such as:

   • Adenosine-to-inosine (A-to-I) editing

   • Cytidine-to-uridine (C-to-U) editing

These changes can alter the amino acid sequence of the protein product, potentially affecting its function or activity.

 Why Option 1 is Correct

“Deletion, insertion or chemical modification of nucleotides that are present in the mRNA”

This accurately describes RNA editing, which modifies already-transcribed mRNA. The changes happen after transcription but before translation, affecting how the RNA is interpreted by the ribosome.

 Why Other Options Are Incorrect

• Option 2: Joining of exons from one pre-mRNA molecule

  • This is alternative splicing, not RNA editing.

• Option 3: Editing of nucleotides in the gene

  • That would be DNA mutation, not RNA editing.

• Option 4: Joining of exons from two pre-mRNAs

  • This is trans-splicing, another rare RNA process, not RNA editing.

 Significance of RNA Editing

• Increases genetic diversity without changing the underlying DNA

• Plays key roles in neurological functions, immune responses, and viral defense

• Misregulation of RNA editing is linked to diseases like cancer and neurological disorders

 Examples

• In humans, ADAR enzymes perform A-to-I editing, especially in the brain.

• In trypanosomes, extensive RNA editing occurs through guide RNAs in mitochondria.

 Conclusion

RNA editing is a fascinating biological process that redefines the central dogma by allowing RNA, not just DNA, to dictate protein diversity. It enables cells to adapt and fine-tune gene expression in highly specific and dynamic ways.