Directions: In the following questions a statement of assertion (A) i...
Primary transcripts contains both introns and exon, in which introns are noncoding
parts.
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Directions: In the following questions a statement of assertion (A) i...
Assertion (A): Primary transcripts in eukaryotes are non-functional.
Reason (R): Methyl guanosine triphosphate is attached to the 5’ – end of hnRNA.
The correct answer is option B: Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
Explanation:
Primary Transcripts in Eukaryotes:
- Primary transcripts, also known as heterogeneous nuclear RNA (hnRNA), are RNA molecules that are initially transcribed from DNA in the nucleus of eukaryotic cells.
- Primary transcripts undergo several modifications before they become functional mRNA molecules that can be translated into proteins.
- These modifications include the addition of a 5' cap and a poly-A tail, as well as the removal of introns through a process called splicing.
Methyl Guanosine Triphosphate (m7GTP) and hnRNA:
- Methyl guanosine triphosphate (m7GTP) is a modified nucleotide that is attached to the 5' end of hnRNA.
- This modification is known as the 5' cap and plays several important roles in the processing and stability of hnRNA.
- The 5' cap protects the RNA molecule from degradation by exonucleases and helps in the efficient export of hnRNA from the nucleus to the cytoplasm.
- It also plays a role in the initiation of translation by interacting with the translation initiation factors.
Non-functionality of Primary Transcripts:
- Primary transcripts, or hnRNA, are considered non-functional because they undergo several modifications before they can be translated into proteins.
- The addition of the 5' cap is one of these modifications and is essential for the processing and stability of hnRNA.
- However, the presence of the 5' cap alone does not make the primary transcript functional.
- The primary transcript still needs to undergo splicing to remove introns and the addition of a poly-A tail before it can be considered as mature mRNA.
- It is the mature mRNA molecules that are functional and can be translated into proteins.
Conclusion:
- In conclusion, while both the assertion and the reason are true, the reason does not provide a correct explanation for the non-functionality of primary transcripts in eukaryotes.
- The non-functionality of primary transcripts is due to the fact that they require additional modifications, such as splicing and the addition of a poly-A tail, before they can be considered as mature mRNA molecules.
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