Which of the following are the post-transcriptional events in an eukaryotic cell?
A. Transport of pre-mRNA to cytoplasm prior to splicing.
B. Removal of introns and joining of exons.
C. Addition of methyl group at 5’ end of hnRNA.
D. Addition of adenine residues at 3’ end of hnRNA.
E. Base pairing of two complementary RNAs.
Choose the correct answer from the options given below: 

The correct answer is B, C, D only

Concept:

• Post-transcriptional events refer to processes that occur after the transcription of DNA into RNA in eukaryotic cells. These events are important for converting the primary RNA transcript (hnRNA or pre-mRNA) into a functional and mature mRNA that can be translated into proteins.
• These processes include modifications to the RNA molecule to ensure its stability, proper functioning, and transport to the cytoplasm for translation.

Explanation:

Option B: Removal of introns and joining of exons:

• This process is known as RNA splicing, where non-coding sequences (introns) are removed and coding sequences (exons) are joined together.
• Splicing is essential for producing a continuous coding sequence that can be translated into a functional protein.

Option C: Addition of methyl group at 5’ end of hnRNA:

• This modification is known as 5’ capping. A methylated guanine nucleotide is added to the 5’ end of the hnRNA.
• The 5’ cap protects the RNA from enzymatic degradation and aids in ribosome binding during translation.

Option D: Addition of adenine residues at 3’ end of hnRNA:

• This process is called polyadenylation, where a poly(A) tail (a sequence of adenine residues) is added to the 3’ end of the hnRNA.
• The poly(A) tail enhances RNA stability and facilitates its export from the nucleus to the cytoplasm.

Fig:Process of Transcription in Eukaryotes

Other options:

Option A: Transport of pre-mRNA to cytoplasm prior to splicing:

• This is incorrect because splicing occurs in the nucleus, and only mature mRNA (after splicing) is transported to the cytoplasm.

Option E: Base pairing of two complementary RNAs:

• This is not a post-transcriptional event in eukaryotic cells. Base pairing of complementary RNAs occurs in processes like RNA interference (RNAi) or double-stranded RNA formation in viral replication.