🔬biological chemistry i review

key term - 3' poly-A tail

Definition

The 3' poly-A tail is a string of adenine nucleotides added to the 3' end of a newly synthesized messenger RNA (mRNA) molecule. This modification plays a crucial role in RNA stability, nuclear export, and translation efficiency, making it essential for proper gene expression.

5 Must Know Facts For Your Next Test

  1. The addition of the poly-A tail occurs after transcription and is catalyzed by an enzyme called poly-A polymerase.
  2. The length of the poly-A tail can vary, typically ranging from 50 to over 250 adenine residues.
  3. Poly-A tails enhance the stability of mRNA by protecting it from degradation by exonucleases in the cytoplasm.
  4. The poly-A tail plays a key role in facilitating the export of mRNA from the nucleus to the cytoplasm, where translation occurs.
  5. The presence of a poly-A tail is a critical signal for the ribosome to recognize and translate mRNA into protein.

Review Questions

  • How does the 3' poly-A tail contribute to the stability and translation of mRNA?
    • The 3' poly-A tail enhances mRNA stability by providing a buffer against degradation from exonucleases in the cytoplasm. By protecting the mRNA, the poly-A tail ensures that it remains intact long enough for translation to occur. Additionally, the poly-A tail aids in the recruitment of ribosomes for translation, facilitating the efficient synthesis of proteins from the mRNA template.
  • What is the process through which the 3' poly-A tail is added to pre-mRNA, and what role does this play in gene expression?
    • The 3' poly-A tail is added to pre-mRNA during RNA processing after transcription. An enzyme known as poly-A polymerase adds a series of adenine nucleotides to the 3' end of the transcript. This modification not only increases mRNA stability but also promotes efficient nuclear export and enhances translation. The addition of the poly-A tail is therefore crucial for regulating gene expression and ensuring proper protein synthesis.
  • Evaluate the impact of mutations that affect poly-A tail addition on overall cellular function and gene regulation.
    • Mutations that disrupt the addition or length of the poly-A tail can severely impair cellular function by destabilizing mRNA molecules or preventing their proper export from the nucleus. Such defects can lead to reduced protein synthesis, altered levels of gene expression, and ultimately affect various cellular processes. The inability to generate stable mRNA could result in diseases or developmental issues, highlighting how vital the poly-A tail is for maintaining normal cellular activities and regulatory mechanisms.

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