In RNA interference (RNAi), how do microRNAs (miRNAs) primarily function to control gene expression in animals?

• A. They bind directly to DNA promoter regions to block RNA polymerase II binding and prevent transcription initiation.
• B. They act as tRNA-like adaptor molecules that change codon recognition during translation to alter protein sequence.
• C. They are translated into small peptides that inhibit ribosome assembly on specific mRNAs.
• D. They are processed and loaded into RISC, then base-pair with target mRNAs (usually imperfectly) to repress translation and/or promote mRNA degradation.

Answer: (D)

Verified step by step guidance

1. Understand that microRNAs (miRNAs) are small non-coding RNA molecules involved in post-transcriptional regulation of gene expression in animals.
2. Recognize that miRNAs do not bind directly to DNA or affect transcription initiation; instead, they function after mRNA has been produced.
3. Know that miRNAs are processed from precursor transcripts and incorporated into a protein complex called the RNA-induced silencing complex (RISC).
4. Learn that within RISC, miRNAs base-pair with complementary sequences on target messenger RNAs (mRNAs), usually with imperfect matching in animals.
5. Realize that this base-pairing leads to repression of translation and/or promotion of mRNA degradation, thereby reducing the expression of the target gene.