“READING” DNA

The DNA-replicating robots trundle off the scene. Another machine appears. It too moves along a stretch of DNA, but more slowly. You see the DNA rope entering one end of this machine and emerging from the other​—unchanged. But a single strand, a new one, is coming out of a separate opening in the machine, like a growing tail. What is going on?

Again the narrator provides an explanation: “DNA’s second job is called transcription. The DNA never leaves the safe shelter of the nucleus. So how can its genes​—the recipes for all the proteins your body is made of—​ever be read and used? Well, this enzyme machine finds a spot along the DNA where a gene has been switched on by chemical signals coming in from outside the cell nucleus. Then this machine uses a molecule called RNA (ribonucleic acid) to make a copy of that gene. RNA looks a lot like a single strand of DNA, but it is different. Its job is to pick up the information coded in the genes. The RNA gets that information while in the enzyme machine, then exits the nucleus and heads to one of the ribosomes, where the information will be used to build a protein.”