3' poly-A tail

Definition

The 3' poly-A tail is a string of adenine nucleotides added to the 3' end of a pre-mRNA molecule during RNA processing. This modification plays a crucial role in enhancing the stability of mRNA, facilitating its export from the nucleus to the cytoplasm, and aiding in the translation process. The presence of the poly-A tail is essential for the proper functioning of eukaryotic genes, as it influences mRNA lifespan and translation efficiency.

5 Must Know Facts For Your Next Test

1. The addition of the poly-A tail occurs after transcription and is catalyzed by the enzyme polyadenylate polymerase.
2. The length of the poly-A tail can vary significantly, influencing the stability and translational efficiency of the mRNA molecule.
3. The poly-A tail helps prevent degradation by exonucleases, enzymes that can degrade RNA from the ends.
4. Eukaryotic cells utilize the poly-A tail as a signal for nuclear export, allowing mRNA to move from the nucleus to the cytoplasm where translation occurs.
5. In some cases, mRNAs with shorter poly-A tails are more likely to be degraded quickly, while longer tails are associated with increased translation rates.

Review Questions

• How does the 3' poly-A tail influence the stability and longevity of mRNA in eukaryotic cells?
  • The 3' poly-A tail significantly enhances mRNA stability by protecting it from degradation by exonucleases. Longer poly-A tails tend to correlate with increased resistance to degradation, allowing the mRNA to persist longer in the cytoplasm. This stability is crucial for ensuring that there is enough functional mRNA available for translation into proteins when needed.
• Discuss how the addition of a 3' poly-A tail affects the translation process of eukaryotic mRNA.
  • The 3' poly-A tail plays an important role in translation by aiding ribosome binding at the mRNA's 5' end through interactions with proteins that recognize the poly-A binding protein. This interaction not only facilitates initiation but also helps in forming a circular structure that enhances translation efficiency. Thus, having a well-structured poly-A tail can directly impact how effectively an mRNA is translated into protein.
• Evaluate the implications of altering poly-A tail length on gene expression and cellular function.
  • Altering the length of the poly-A tail can have profound effects on gene expression and cellular function. Shortening the poly-A tail may lead to rapid degradation of mRNA, resulting in decreased protein synthesis and potentially disrupting cellular processes. Conversely, extending the poly-A tail could enhance mRNA stability and increase translation rates, which might lead to overexpression of certain proteins. This balance is critical for normal cellular functions and maintaining homeostasis within the cell.

Related terms

Pre-mRNA: The initial form of RNA transcript synthesized from DNA that undergoes processing, including splicing and addition of a 5' cap and 3' poly-A tail, before becoming mature mRNA.

5' cap:

A modified guanine nucleotide added to the 5' end of mRNA that protects the RNA from degradation and assists in ribosome binding during translation.

RNA splicing: The process of removing introns from pre-mRNA and joining exons together to form mature mRNA, which is necessary for proper gene expression.