Question

Given below are two statements: Statement (I): Eukaryotes have a 5' cap on their mRNAs; prokaryotes do not have the same. Statement (II): Messenger RNAs of eukaryotes generally have a 3' poly-A tail; prokaryotic mRNAs do not have the same. In light of the above statements, choose the most appropriate answer from the options given below:

• A. Both Statement (I) and Statement (II) are correct.
• B. Both Statement (I) and Statement (II) are incorrect.
• C. Statement (I) is correct but Statement (II) is incorrect.
• D. Statement (I) is incorrect but Statement (II) is correct.

Hint:

Eukaryotic mRNA processing steps:
1. 5' capping (7-methylguanosine)
2. 3' polyadenylation (Poly-A tail)
3. Splicing (removal of introns)
Prokaryotic mRNAs do not undergo these steps.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Post-transcriptional modifications distinguish eukaryotic gene expression from prokaryotic gene expression.
In eukaryotes, pre-mRNA synthesized in the nucleus must be modified and processed before being transported to the cytoplasm for translation.
Prokaryotic transcription and translation are coupled in the cytoplasm, occurring simultaneously without requiring modifications.

Step 2: Detailed Explanation:
Let us analyze both statements.
- Statement (I) concerns the 5' cap.
Eukaryotic mRNAs undergo capping at the 5' end with a 7-methylguanosine molecule.
This cap protects the mRNA from degradation, facilitates export from the nucleus, and aids ribosome binding.
Prokaryotic mRNAs do not undergo capping and retain their original 5' triphosphate group.
Thus, Statement (I) is correct.
- Statement (II) concerns the 3' poly-A tail.
Eukaryotic mRNAs are polyadenylated at the 3' end, adding a tail of multiple adenine residues that stabilizes the molecule.
In prokaryotes, stable poly-A tails do not exist as a general feature.
When polyadenylation occasionally occurs in prokaryotic mRNA, it acts as a signal for degradation rather than stabilization.
Thus, prokaryotic mRNAs do not have the same stable poly-A tail structure.
Thus, Statement (II) is correct.
Therefore, both Statement (I) and Statement (II) are correct.

Step 3: Final Answer:
Both Statement (I) and Statement (II) are correct, corresponding to option 1.