Final answer:
The protein known as Dicer is responsible for chopping up the initial long, double-stranded RNA found in the cell, as part of the RNA interference (RNAi) defense mechanism against foreign RNA elements.
Step-by-step explanation:
The initial long, double-stranded RNA found in the cell is chopped up by a protein known as Dicer. When cells encounter double-stranded RNAs, such as those from certain viral infections, the Dicer enzyme acts as a defense mechanism, hydrolyzing the dsRNA into short fragments. These fragments, or short interfering RNAs (siRNAs), are then incorporated into the RNA-induced silencing complex (RISC), targeting corresponding mRNA molecules for degradation and preventing the production of viral proteins.
In a broader context, DICER is part of a cellular process known as RNA interference (RNAi), which plays a critical role in regulating gene expression and maintaining the stability of the genome by silencing potentially harmful foreign RNA elements.