RNA is a naturally produced molecule in the body that is involved in the process of converting the genetic information encoded in DNA into protein products (i.e., in gene expression). Its structure is very similar to that of DNA. However, whereas DNA typically consists of two chains, or strands, of building blocks (i.e., nucleotides) sticking together, RNA normally is a single-stranded molecule. When a gene is expressed, the genetic information from one strand of DNA is first copied into a complementary RNA molecule known as messenger RNA (mRNA). The mRNA molecule then travels into a different region of the cell, where it serves as a template for the production of a protein molecule in a process called translation. However, if the mRNA is degraded before it can be used to produce protein molecules, the expression of the corresponding gene is prevented—a phenomenon known as silencing. siRNA does just that: It can interact with a specific, complementary mRNA, thereby inducing its degradation or at least repressing translation.