MicroRNAs

Definition

MicroRNAs (miRNAs) are small, non-coding RNA molecules, typically 21-25 nucleotides in length, that play a crucial role in regulating gene expression post-transcriptionally. They achieve this by binding to complementary sequences on messenger RNA (mRNA), leading to mRNA degradation or inhibition of translation, which ultimately influences various biological processes such as development, cell differentiation, and apoptosis.

5 Must Know Facts For Your Next Test

1. MicroRNAs are encoded by specific genes in the genome and are transcribed as primary miRNAs (pri-miRNAs) before being processed into mature miRNAs.
2. The processing of pri-miRNAs involves the action of the Drosha enzyme, which cleaves them into precursor miRNAs (pre-miRNAs), followed by Dicer enzyme action to produce the mature miRNA.
3. MicroRNAs can target multiple mRNAs and can be involved in the regulation of entire gene networks, making them key players in fine-tuning cellular responses.
4. The dysregulation of microRNAs has been associated with various diseases, including cancer, where they can act as either tumor suppressors or oncogenes.
5. MicroRNAs are found in various organisms, from plants to animals, and play essential roles in developmental processes, stress responses, and metabolic regulation.

Review Questions

• How do microRNAs influence gene expression after transcription?
  • MicroRNAs influence gene expression by binding to complementary sequences on messenger RNA (mRNA). This binding can lead to mRNA degradation or inhibit the translation process, effectively silencing the expression of target genes. As a result, microRNAs serve as critical regulators that help control the levels of proteins synthesized within a cell.
• What are the steps involved in the processing of microRNAs from their primary form to their mature form?
  • The processing of microRNAs begins with transcription from specific genes into primary miRNAs (pri-miRNAs). The Drosha enzyme then cleaves these pri-miRNAs into shorter precursor miRNAs (pre-miRNAs) within the nucleus. Afterward, the pre-miRNAs are transported to the cytoplasm where the Dicer enzyme further processes them into mature microRNAs. This maturation is crucial for their functional role in regulating gene expression.
• Evaluate the impact of dysregulated microRNA expression on cellular function and disease progression.
  • Dysregulated expression of microRNAs can significantly impact cellular functions and contribute to disease progression. For instance, when microRNAs that normally act as tumor suppressors are downregulated, it can lead to increased oncogene activity and promote cancer development. Conversely, overexpression of certain microRNAs may inhibit tumor suppressor genes, further advancing malignancy. This dual role underscores the complexity of microRNA function and their potential as therapeutic targets in various diseases.

Related terms

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

RNA interference: RNA interference (RNAi) is a biological process in which RNA molecules inhibit gene expression or translation by targeting specific mRNA molecules for degradation.

Transcription factors: Transcription factors are proteins that bind to specific DNA sequences to regulate the transcription of genes, influencing gene expression before mRNA is produced.