Question

The addition of poly(A) tails to 3' end is a characteristic feature of:

• A. Translation
• B. Transcription
• C. Post-translational modification
• D. Post-transcriptional modification

Hint:

Remember the central dogma flow: DNA $\rightarrow$ Transcription $\rightarrow$ pre-mRNA $\rightarrow$ Post-transcriptional modification $\rightarrow$ mRNA $\rightarrow$ Translation $\rightarrow$ Protein $\rightarrow$ Post-translational modification. Placing polyadenylation in this sequence helps identify it correctly.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Gene expression in eukaryotes involves several steps. First, a gene is transcribed from DNA into a precursor messenger RNA (pre-mRNA). This pre-mRNA then undergoes several modifications before it becomes a mature messenger RNA (mRNA) that can be translated into a protein. These modifications are collectively known as post-transcriptional modification.
Step 2: Detailed Explanation:
- Transcription: This is the process of creating an RNA copy of a gene sequence from a DNA template. The immediate product is a primary transcript or pre-mRNA.
- Post-transcriptional modification: After transcription, the pre-mRNA is processed into mature mRNA. This process includes three main events:
1. 5' Capping: A modified guanine nucleotide is added to the 5' end.
2. Splicing: Introns (non-coding regions) are removed, and exons (coding regions) are joined together.
3. Polyadenylation: A tail of multiple adenine nucleotides (a poly-A tail) is added to the 3' end of the RNA transcript. This process is crucial for the stability, nuclear export, and translation of the mRNA.
- Translation: This is the process where the genetic code carried by mRNA is decoded to produce a specific sequence of amino acids in a polypeptide chain. It occurs after post-transcriptional modifications are complete.
- Post-translational modification: This refers to the chemical modification of a protein after its synthesis during translation.
Step 3: Final Answer:
The addition of a poly(A) tail to the 3' end is a key step that happens to the RNA transcript after it has been synthesized (transcribed) but before it is translated. Therefore, it is a characteristic feature of post-transcriptional modification.