What is the approximate size of miRNA molecules produced by Dicer nuclease?
## Core Concept
MicroRNAs (miRNAs) are small non-coding RNAs that play a crucial role in post-transcriptional regulation of gene expression. They are processed from longer precursor molecules by the enzyme Dicer, a type III endoribonuclease. The size of mature miRNA molecules is critical for their function and interaction with target messenger RNAs (mRNAs).
## Why the Correct Answer is Right
Dicer nuclease processes precursor miRNAs (pre-miRNAs) into mature miRNAs. The mature miRNAs produced by Dicer are approximately 20-25 nucleotides in length. This specific size range is essential for the miRNAs to bind to the 3'-untranslated region (3'-UTR) of target mRNAs, leading to their degradation or inhibition of translation. The 20-25 nucleotide size range allows for specific recognition and binding to target sequences while being small enough to be processed by Dicer and loaded into the RNA-induced silencing complex (RISC).
## Why Each Wrong Option is Incorrect
**Option A:** 10-15 nucleotides - This size is too small for miRNAs. While there are smaller RNAs involved in RNA interference (RNAi), such as piRNAs (piwi-interacting RNAs) which can be around 24-31 nucleotides but often associated with a different Argonaute protein, typical miRNAs are larger.
**Option B:** 30-35 nucleotides - This size is too large for mature miRNAs. While precursor miRNAs can be around this size, Dicer processing results in a smaller product.
**Option D:** 40-45 nucleotides - This is much too large for mature miRNAs and more representative of the size of some precursor miRNAs before Dicer processing.
## Clinical Pearl / High-Yield Fact
A key point to remember is that the size of miRNAs (20-25 nucleotides) is critical for their function, and Dicer is a key enzyme in their biogenesis. Dysregulation of miRNAs has been implicated in various diseases, including cancer, cardiovascular disease, and neurological disorders. Understanding miRNA biogenesis and function can provide insights into potential therapeutic targets.
**Correct Answer: C. 20-25 nucleotides.**