Question

Genes encoding microRNA can be located bioinformatically in the genome by which of the following method?

• A. By ORF scanning
• B. By identifying their typical secondary structure
• C. By analyzing their nucleotide sequence
• D. Can not be predicted by bioinformatics approaches

Hint:

Coding Genes = ORF Scanning (Search for ATG...TAA).
Non-coding RNA (miRNA/tRNA) = Secondary Structure Folding (Search for Hairpins/Loops).
Structure dictates function and identification for non-coding RNAs!

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
MicroRNAs (miRNAs) are small, non-coding RNA molecules (~21-24 nt) that regulate gene expression post-transcriptionally. The question asks how bioinformatics tools can distinguish miRNA-encoding genes from other regions of the genome.

Step 2: Detailed Explanation:

• The miRNA Biogenesis Pathway: miRNA genes are transcribed into long "pri-miRNAs," which are then processed into ~70 nt "pre-miRNAs."

• Structural Characteristic: The defining feature of pre-miRNA is its ability to fold into a stable, stem-loop (hairpin) secondary structure. This structure is a prerequisite for recognition by the processing enzyme Dicer (or DCL in plants).

• Bioinformatic Prediction: Because miRNAs are non-coding, they lack Open Reading Frames (ORFs). Therefore, "ORF scanning" (Option A), which looks for start and stop codons, is useless.

• Computational Algorithms: Tools like miRDeep, MiRanda, and various SVM-based predictors scan the genome for sequences that, when computationally "folded" (using algorithms like Mfold), produce hairpins with specific thermodynamic stability (low minimum free energy).

• Sequence Conservation: While nucleotide sequence analysis (Option C) helps identify known miRNAs across species (homology), it is not the primary method for locating or discovering novel miRNA genes within a genome without the structural context.

Step 3: Final Answer:
Bioinformatic identification of miRNA genes relies primarily on detecting the characteristic hairpin secondary structures formed by their precursor transcripts.