Polyadenylation

Definition

Polyadenylation is the process by which a poly(A) tail, a sequence of adenine nucleotides, is added to the 3' end of a newly synthesized RNA molecule. This modification plays a critical role in stabilizing the RNA, enhancing its translation into protein, and regulating its degradation. Polyadenylation is an essential step in RNA processing that ensures proper gene expression and affects the stability and lifespan of mRNA in the cytoplasm.

5 Must Know Facts For Your Next Test

1. Polyadenylation typically occurs after transcription in eukaryotic cells, specifically for mRNA molecules.
2. The length of the poly(A) tail can influence the stability and translation efficiency of the mRNA, with longer tails generally leading to increased stability.
3. Polyadenylation involves specific sequences in the RNA called polyadenylation signals, which are recognized by cellular machinery that adds the adenine nucleotides.
4. In addition to mRNA, some non-coding RNAs can also undergo polyadenylation, impacting their function and stability.
5. Defects in polyadenylation can lead to various diseases, including certain cancers and genetic disorders, highlighting its importance in cellular regulation.

Review Questions

• How does polyadenylation affect the stability and functionality of mRNA molecules?
  • Polyadenylation increases the stability of mRNA by adding a poly(A) tail at its 3' end, which protects it from enzymatic degradation. This modification not only enhances the mRNA's longevity in the cytoplasm but also plays a critical role in facilitating efficient translation into proteins. The length of the poly(A) tail can further influence how long the mRNA remains functional before being degraded.
• Discuss the mechanisms by which cells recognize and carry out polyadenylation on pre-mRNA transcripts.
  • Cells recognize specific polyadenylation signals within pre-mRNA transcripts, which include a consensus sequence often characterized by 'AAUAAA'. Once this signal is identified, various proteins and enzymes, including cleavage and polyadenylation factors (CPF), are recruited to carry out cleavage of the pre-mRNA. Following cleavage, poly(A) polymerase adds adenine nucleotides to create the poly(A) tail, completing the polyadenylation process.
• Evaluate the implications of disrupted polyadenylation processes on gene expression and potential disease development.
  • Disruption of polyadenylation can lead to improper mRNA processing, resulting in unstable or dysfunctional mRNA molecules. This can severely affect gene expression levels and ultimately impact protein synthesis. Such defects are implicated in various diseases, including cancers and genetic disorders, as altered levels of specific proteins can disrupt normal cellular functions and pathways. Understanding these implications underscores the essential nature of polyadenylation in maintaining cellular health and regulation.

Related terms

mRNA:

Messenger RNA (mRNA) is a type of RNA that conveys genetic information from DNA to the ribosome, where proteins are synthesized.

RNA polymerase: RNA polymerase is the enzyme responsible for synthesizing RNA from a DNA template during transcription.

splicing:

Splicing is the process of removing introns from a pre-mRNA transcript and connecting the remaining exons to form mature mRNA.