Final answer:
MicroRNAs (miRNAs) are processed in the cytoplasm and remain there to repress translation or degrade mRNAs by associating with the RISC complex, not in the nucleus as suggested by the initial question.
Step-by-step explanation:
False. The initial assumption in the student's question is incorrect. After initial processing in the cytoplasm, miRNAs do not import into the nucleus to bind to pre-mRNAs. Instead, they function in the cytoplasm where they associate with the RISC complex to target mRNAs for degradation or translation repression.
MicroRNAs (miRNAs) are initially transcribed as pre-miRNAs in the nucleus and subsequently processed to mature miRNAs in the cytoplasm. During processing, they lose their stem-loop structure and combine with RISC proteins. This complex then targets mRNAs that are either old, no longer needed, or damaged during transcription for degradation or repression of translation. The mRNA processing includes addition of a 5' cap, poly-A tail, and splicing of introns and exons, which facilitate the mRNA's exit from the nucleus into the cytoplasm, where miRNAs exert their regulatory functions.