Final answer:
The RNA Induced Silencing Complex (RISC) is the protein complex that contains a small guide RNA molecule and is responsible for degrading mRNA. It is a crucial part of the RNA interference mechanism used by cells to regulate gene expression and defend against viral infections.
Step-by-step explanation:
The protein complex that contains a small guide RNA molecule and degrades mRNA is known as the RNA Induced Silencing Complex (RISC). When cells encounter double-stranded RNAs, such as those from a viral invasion, the enzyme DICER is activated to cleave these dsRNAs into short fragments. One strand of these fragments, either an siRNA or miRNA, is then incorporated into the RISC. The resulting siRNA-RISC or miRNA-RISC complex binds to their target mRNA with a complementary sequence, leading to the degradation of the mRNA or the inhibition of translation, respectively. This process is part of the natural regulatory mechanism of RNA interference (RNAi), which prevents the synthesis of proteins by guiding the breakdown of specific mRNA molecules.