The events happening during RNA processing are:
A. Capping at the 5'-end.
B. Proof-reading of the nascent mRNA.
C. Splicing of the introns and joining of the exons.
D. Deadenylation at the 3'-end.
E. Addition of poly-A tail at the 3'-end.
Choose the correct answer from the options given below
A. Capping at the 5'-end.
B. Proof-reading of the nascent mRNA.
C. Splicing of the introns and joining of the exons.
D. Deadenylation at the 3'-end.
E. Addition of poly-A tail at the 3'-end.
Choose the correct answer from the options given below
Show Hint
Remember that these processes occur exclusively in the nucleus before the mRNA reaches the cytoplasm.
- A-B-D
- A-C-E
- B-D-E
- B-C-D
The Correct Option is B
Solution and Explanation
The question focuses on the post-transcriptional modifications that occur in eukaryotic cells to convert pre-mRNA (primary transcript) into mature mRNA.
These processes are essential for the stability, transport, and translation of the mRNA.
Step 2: Detailed Explanation:
• 5' Capping (A): Shortly after transcription begins, a 7-methylguanosine cap is added to the 5' end of the nascent mRNA.
This cap protects the mRNA from degradation by exonucleases and serves as a recognition signal for the ribosome during translation initiation.
• Splicing (C): Eukaryotic genes are "split," containing coding regions called exons and non-coding regions called introns.
During splicing, the introns are removed, and the exons are ligated together by a complex called the spliceosome.
This ensures that the mRNA contains a continuous coding sequence for the protein.
• 3' Polyadenylation (E): Once transcription is terminated, a string of adenine residues (poly-A tail) is added to the 3' end by the enzyme poly-A polymerase.
The poly-A tail enhances mRNA stability and assists in its export from the nucleus to the cytoplasm.
• Incorrect Events (B and D):
Proof-reading (B) is a characteristic of DNA replication (DNA polymerases) to ensure high fidelity; it is not a standard component of RNA processing.
Deadenylation (D) is the removal of the poly-A tail, which is actually an initial step in mRNA degradation (decay), not its processing/maturation.
Final Answer:
The standard RNA processing events are capping (A), splicing (C), and polyadenylation (E).
The correct combination is A-C-E, which is found in option (B).
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