This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: DNB 2018, Subject name: Biochemistry
miRNA binding site for gene knock down? 
Select and explain. 
A. 3' untranslated region, B. 5' untranslated region, C. Introns, D. Both 3' and 5' untranslated region
A: 3' untranslated region
Answer: A: 3' untranslated region 
Explanation: In higher eukaryotes a class of small RNAs knows as micro RNA (miRNA) that mediates the silencing of paicular genes. The RNAs function by interacting with mRNAs, often in the 3' Untranslated region, resulting in either mRNA degradation or translation inhibition. In either case, the mRNA, and thus the gene that produces it, is silenced. The process is known as RNA interference. miRNAs: MicroRNAs, 21 to 22 nucleotide long RNA species derived primarily from RNA polymerase II transcription units, RNA processing. These RNAs play crucial roles in gene regulation by altering mRNA function.