631190-12-41P AID: 2498 | 25/08/2015
RNA (ribonucleic acid) once produced in a cell rapidly degraded by ribonucleases after synthesizing required protein. This is called post-transcriptional gene repression. If the RNA is not degraded, then it produces protein in an uncontrolled manner.
miRNAs are endogenously synthesized ~21 nucleotide non-coding RNAs. They participate in regulation of the translation. So their expression is tightly controlled. In the cytoplasm, the pre-miRNA hairpin is cleaved by an enzyme called RNAase III (dicer).
This enzyme interacts with the 3’end of the hairpin and cleaves the loop that joins the 3’and 5’arms. This yields a double stranded duplex form of miRNA. Only one strand of this duplex is incorporated into the RNA-induced silencing complex (RISC), by which miRNA targets it’s mRNA.
Hence, the correct option is (d) b and c are both correct.