key term - Poly-A tail

Definition

A poly-A tail is a stretch of adenine nucleotides added to the 3' end of a pre-mRNA molecule during the processing of eukaryotic genes. This modification plays a crucial role in stabilizing the mRNA, facilitating its transport from the nucleus to the cytoplasm, and enhancing its translation into protein. The addition of the poly-A tail is an essential step in RNA processing that ensures mRNA stability and efficiency in protein synthesis.

5 Must Know Facts For Your Next Test

1. The poly-A tail typically consists of 50 to 250 adenine residues, and its length can influence the stability and lifespan of the mRNA in the cytoplasm.
2. Polyadenylation is catalyzed by the enzyme poly-A polymerase, which adds adenine nucleotides after the cleavage of the pre-mRNA at a specific site.
3. The presence of a poly-A tail is vital for efficient translation, as it aids in the recognition of the mRNA by ribosomes.
4. In addition to providing stability, the poly-A tail also plays a role in the export of mRNA from the nucleus to the cytoplasm.
5. Some mRNAs undergo alternative polyadenylation, resulting in different lengths of poly-A tails, which can impact gene expression and protein function.

Review Questions

• How does the addition of a poly-A tail contribute to mRNA stability and functionality?
  • The addition of a poly-A tail to mRNA enhances its stability by protecting it from degradation by exonucleases in the cytoplasm. The poly-A tail also facilitates the recognition of the mRNA by ribosomes, which is crucial for efficient translation into proteins. Without a proper poly-A tail, mRNA molecules would be more susceptible to degradation, leading to reduced protein synthesis.
• Discuss how polyadenylation interacts with other RNA processing events such as capping and splicing.
  • Polyadenylation works alongside other RNA processing events like capping and splicing to produce mature mRNA. While capping occurs at the 5' end and protects against degradation, splicing removes non-coding introns and joins coding exons together. The addition of the poly-A tail at the 3' end complements these processes by ensuring that the mature mRNA is stable, properly processed, and ready for translation in the cytoplasm.
• Evaluate the implications of alternative polyadenylation on gene expression and protein diversity.
  • Alternative polyadenylation allows for different lengths of poly-A tails on mRNAs derived from the same gene, which can lead to variations in mRNA stability, localization, and translational efficiency. This variability can significantly influence gene expression patterns and result in the production of different protein isoforms from a single gene. Consequently, alternative polyadenylation contributes to proteomic diversity and allows cells to adapt their protein outputs in response to developmental cues or environmental changes.

Related terms

5' cap: A modified guanine nucleotide added to the 5' end of eukaryotic mRNA, which protects the mRNA from degradation and assists in ribosome binding during translation.

mRNA splicing: The process by which introns are removed and exons are joined together in pre-mRNA to form a mature mRNA molecule ready for translation.

RNA polymerase II: An enzyme responsible for synthesizing mRNA from a DNA template during transcription in eukaryotic cells.