Page 136 - The Cell in 40 Topics

The Cell in 40 Topics

has to be overcome. The entwined arms of the DNA molecule need to be
separated, and this is again the task of RNA polymerase. Attaching itself to
the first 3 letters of the gene to be coded, the RNA polymerase opens up the
DNA rungs—which resemble a spiral staircase—as if it were unfastening a
zipper. It does this at a very great speed. In fact, because of that very speed,
there is a danger of the DNA heating up and getting damaged. Yet the sys-
tem has been laid out so perfectly that this danger has been foreseen.
Thanks to a series of precautions taken beforehand, the danger of
overheating is eliminated; as if it were aware of the possible danger, a spe-
cial enzyme attaches to the ends of the opened DNA string and blocks this
friction. As we’ve seen, special enzymes then prevent them winding
around each other during the DNA opening process. Were it not for these
enzymes, then it would be impossible for the order docket known as mes-
senger RNA to be copied, because the arms of the DNA helix, parted like the
teeth of a zipper, would again wind around each other before the copying
process even began, and the resulting friction would damage the structure

As the arms of the DNA separate from one another, an enzyme
prevents them winding around one another again. This enzyme is
marked with green in the illustration.

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