key term - Mirna

Definition

MicroRNA (miRNA) is a small, non-coding RNA molecule, typically about 22 nucleotides long, that plays a critical role in regulating gene expression by binding to complementary sequences in messenger RNA (mRNA). By interfering with mRNA translation or promoting its degradation, miRNAs are essential for various cellular processes, including development, differentiation, and response to stress.

5 Must Know Facts For Your Next Test

1. miRNAs are derived from longer primary transcripts called pri-miRNAs, which are processed into precursor miRNAs (pre-miRNAs) before being further cleaved into mature miRNAs by the enzyme Dicer.
2. Each miRNA can target multiple mRNAs, leading to widespread regulatory effects on various biological pathways.
3. The binding of miRNAs to their target mRNAs typically occurs at the 3' untranslated region (3' UTR), which is crucial for the post-transcriptional regulation of gene expression.
4. Altered expression levels of specific miRNAs have been implicated in various diseases, including cancer, cardiovascular diseases, and neurological disorders.
5. miRNAs are also involved in epigenetic regulation, influencing the chromatin structure and stability of specific genes beyond direct mRNA interaction.

Review Questions

• How do miRNAs influence gene expression at the molecular level?
  • miRNAs influence gene expression primarily by binding to complementary sequences in target mRNAs. This interaction can lead to two outcomes: either the degradation of the mRNA or inhibition of its translation into protein. By affecting mRNA stability and translation efficiency, miRNAs play a pivotal role in fine-tuning the levels of proteins produced within the cell.
• Discuss the role of Dicer in the biogenesis of miRNAs and its importance in cellular functions.
  • Dicer is essential for the maturation of miRNAs from their precursor forms. It cleaves the pre-miRNA into mature miRNA fragments that can then participate in the RNA-induced silencing complex (RISC). This processing step is crucial because without Dicer's activity, miRNAs would not be produced correctly, leading to disrupted regulation of gene expression and potentially resulting in various cellular dysfunctions.
• Evaluate the implications of altered miRNA expression profiles in disease states such as cancer.
  • Altered miRNA expression profiles can have profound implications in diseases like cancer. For example, certain miRNAs may act as tumor suppressors when they are downregulated or as oncogenes when upregulated. These changes can disrupt normal cell signaling pathways and contribute to uncontrolled cell growth and proliferation. Understanding these altered profiles offers potential avenues for therapeutic interventions, such as restoring normal miRNA function or targeting specific miRNAs for treatment.

Related terms

mRNA:

Messenger RNA (mRNA) is a type of RNA that conveys genetic information from DNA to the ribosome, where it serves as a template for protein synthesis.

RNA interference:

RNA interference (RNAi) is a biological process in which small RNA molecules, like siRNA and miRNA, inhibit gene expression by degrading mRNA or blocking its translation.

Dicer: Dicer is an enzyme that processes long double-stranded RNA and pre-miRNAs into short, functional miRNAs and siRNAs that can engage in gene silencing.