Post-transcriptional modifications of RNA refer to the chemical modifications that occur on RNA molecules after they have been transcribed from DNA but before they are either translated into proteins or used for other cellular functions. These modifications are important for regulating gene expression and ensuring the proper functioning of RNA molecules. Some of the common post-transcriptional modifications include:
1. Addition of a 5' cap: The addition of a 7-methylguanosine cap at the 5' end of mRNA protects the mRNA from degradation and plays a role in facilitating translation.
2. Addition of a poly(A) tail: The addition of a polyadenylate [poly(A)] tail at the 3' end of mRNA protects the mRNA from degradation and is involved in the export of mRNA from the nucleus to the cytoplasm.
3. RNA splicing: In eukaryotes, most mRNA molecules undergo splicing, where noncoding introns are removed, and exons are joined together to form the final mature mRNA. Alternative splicing can generate multiple protein isoforms from a single gene.
4. RNA editing: Some RNA molecules undergo chemical modifications, such as nucleotide substitutions, insertions, or deletions, through a process called RNA editing. This can change the sequence of the mRNA and potentially alter the encoded protein.
5. RNA methylation: Methylation of specific nucleotides, such as adenosine or cytosine, occurs in RNA molecules and can affect RNA stability, localization, and translation efficiency.
6. RNA folding and secondary structure formation: RNA molecules can fold into complex secondary structures through base pairing interactions. This can affect their stability, interaction with other molecules, and ability to function properly.
These post-transcriptional modifications are carried out by specific enzymes and protein complexes and play crucial roles in gene expression regulation, mRNA stability, and protein diversity.
8.Post transcriptional modification of RNA occurring after RNA synthesis
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