Question

What happens to the miRNAs that are bound in a RISC?

A. They remain bound to the RISC, where they can target the elimination of multiple mRNAs.
B. If they include a sufficiently extensive region of complementarity with an mRNA, they are diverted to a region of the cytosol where they are eventually degraded.
C. They are destroyed as soon as they bind to an mRNA.
D. Their translation is blocked.

Answer 1

MicroRNAs (miRNAs) bound in a RISC target complementary mRNA sequences to repress their translation or direct their degradation, thus playing a key role in regulating gene expression at the post-transcriptional level.

Step-by-step explanation:

When microRNAs (miRNAs) are bound to a RISC (RNA-induced silencing complex), they play a crucial role in gene regulation. After processing by proteins such as Dicer, mature miRNAs are incorporated into RISC and guide the complex to complementary mRNA sequences.

Upon binding, the RISC-miRNA complex can either impede the translation of the mRNA or, in cases where there is sufficient base pairing, lead to the mRNA's degradation. This ensures the elimination of old, unnecessary, or damaged mRNAs, precisely regulating protein synthesis and maintaining cellular function.