2.5 miRNA and siRNA

• What is the fourth type of RNA in the cell?

  MicroRNA (miRNA)
• What is the length of miRNA fragments?

  21 to 23 nucleotides
• What is the primary function of miRNA?

  Regulate gene expression
• Why are miRNAs often called noncoding RNA?

  They are not translated into proteins
• How are miRNAs processed in the cell?

  From pri-miRNAs to pre-miRNAs
• What are pri-miRNAs?

  Primary transcripts of the gene
• What is the role of the microprocessor complex?

  Process pri-miRNAs into pre-miRNAs
• What structure do pre-miRNAs form?

  70-nucleotide stem-loop structures
• What enzyme processes pre-miRNAs in the cytoplasm?

  Dicer enzyme
• What does RISC stand for?

  RNA-induced silencing complex
• How do miRNAs regulate gene expression?

  By binding to complementary mRNA regions
• What happens when miRNAs bind to mRNA?

  They promote repression of translation
• What diseases are associated with alterations in miRNA function?

  Cancer and heart disease
• What is another name for small interfering RNA?

  Silencing RNA
• What is the length of siRNA molecules?

  20 to 25 nucleotides
• How do siRNAs interfere with gene expression?

  By blocking translation of specific mRNA
• How are siRNAs designed to avoid processing?

  To bypass the microprocessor complex
• What is the therapeutic potential of siRNAs?

  To silence genes contributing to diseases
• What is the process of miRNA generation?

  1. Transcription of DNA to pri-miRNA
  2. Processing by microprocessor complex to pre-miRNA
  3. Further processing by dicer enzyme to miRNA
  4. Binding to mRNA to regulate gene expression
• What are the differences between miRNA and siRNA?

  • miRNA: single-stranded, regulates gene expression
  • siRNA: double-stranded, interferes with specific gene expression
  • miRNA: endogenous, siRNA: often synthetic