Question

When the RNA within the RISC pairs imperfectly with its target sequence, the mRNA is usually not cleaved; instead, translation of the mRNA is inhibited. RISC-associated RNAs that most frequently have this effect are:

A) siRNAs
B) miRNAs
C) RdRPs
D) tRNAs
E) rRNAs

Answer 1

The RISC-associated RNAs that inhibit translation of mRNA when pairing imperfectly with its target sequence are microRNAs (miRNAs). miRNAs bind to the RNA molecule and to RISC, leading to impaired translation or degradation of the target mRNA. This process varies from the action of siRNAs, which direct the cleavage of completely complementary mRNA sequences.

Step-by-step explanation:

When the RNA within the RNA-induced silencing complex (RISC) pairs imperfectly with its target sequence, the mRNA is typically not cleaved; instead, the process inhibits the translation of the mRNA. The RISC-associated RNAs that most frequently have this effect are microRNAs (miRNAs)

miRNAs are short RNA molecules that are produced as longer pre-miRNAs in the nucleus and then cleaved into mature miRNAs by an enzyme called Dicer. These mature miRNAs recognize specific sequences and bind to the RNA molecule, as well as associate with RISC. The miRNA-RISC complexes impair translation or degrade the target mRNA when bound to target sequences with imperfect complementarity, which is characteristic of miRNA action.

On the other hand, small interfering RNAs (siRNAs) are completely complementary to their target mRNA sequences and direct the RISC to cleave the mRNA, facilitating RNA interference which is a more direct and complete gene silencing compared to the regulatory nature of miRNAs.