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)