3' polyadenylation

Definition

3' polyadenylation is the addition of a long chain of adenine nucleotides, known as a poly(A) tail, to the 3' end of a newly synthesized pre-mRNA molecule. This modification is crucial for the stability, export, and translation of mRNA in eukaryotic cells, significantly impacting gene expression and protein synthesis.

5 Must Know Facts For Your Next Test

1. The poly(A) tail typically consists of 50 to 250 adenine nucleotides, which enhances the stability of mRNA by protecting it from degradation by exonucleases.
2. Polyadenylation occurs after transcription, and is often coupled with other RNA processing events such as capping and splicing.
3. The length of the poly(A) tail can influence the translational efficiency of mRNA, with longer tails generally promoting better translation.
4. In eukaryotes, the enzyme poly(A) polymerase adds the adenine nucleotides to the 3' end during the processing of pre-mRNA into mature mRNA.
5. Defects in polyadenylation can lead to various diseases, including some types of cancer and genetic disorders due to improper mRNA stability and function.

Review Questions

• How does 3' polyadenylation contribute to the overall stability and function of mRNA?
  • 3' polyadenylation contributes to mRNA stability by adding a poly(A) tail that protects the molecule from degradation by exonucleases. The length of this tail can also affect how efficiently the mRNA is translated into protein, with longer tails typically leading to increased translation rates. Additionally, this modification helps in the export of mRNA from the nucleus to the cytoplasm, ensuring that it reaches the ribosomes for protein synthesis.
• Compare and contrast the roles of 3' polyadenylation and capping in RNA processing.
  • Both 3' polyadenylation and capping are essential modifications that occur during RNA processing, but they serve different functions. Capping involves adding a modified guanine nucleotide to the 5' end of pre-mRNA, which is crucial for ribosome recognition and initiation of translation. In contrast, 3' polyadenylation adds a poly(A) tail to the 3' end, enhancing mRNA stability and aiding in nuclear export. Together, these modifications protect the RNA molecule and prepare it for translation.
• Evaluate the implications of defects in 3' polyadenylation on gene expression and potential disease outcomes.
  • Defects in 3' polyadenylation can severely impact gene expression by leading to unstable or improperly processed mRNA. When polyadenylation does not occur correctly, the resulting mRNAs may be more susceptible to degradation or fail to be exported from the nucleus. This can disrupt protein synthesis, contributing to diseases such as certain cancers and genetic disorders where gene expression regulation is compromised. Understanding these implications highlights the importance of proper RNA processing in maintaining cellular function.

Related terms

Pre-mRNA: The initial RNA transcript that is synthesized from a DNA template and undergoes processing to become mature mRNA.

Capping: The addition of a modified guanine nucleotide (the 5' cap) to the beginning of the pre-mRNA, which plays a key role in mRNA stability and initiation of translation.

Splicing: The process of removing introns and joining exons in pre-mRNA, resulting in a mature mRNA molecule that can be translated into a protein.