How can scientists cut and paste DNA?
(Lansing State Journal, February 22, 1995)


Because deoxyribonucleic acid (DNA) is so small, the scientists that work with it have to use tools that are also very small.  In fact, the tools used are generally single molecules themselves.  To understand how molecular biologists (the people who work with DNA and other molecules) use these tiny tools, one first has to understand a little bit about DNA.

DNA is a very special type of molecule.  It is a long thing thread, so thin that it can only be seen with the most powerful microscopes.  The molecule generally has the form of a twisted ladder, called a double helix, and codes the information of living cells in the steps of the ladder.  The steps are called base pairs, and there are essentially four different types.  Different organisms, and even different individuals, have slightly different base pair sequences.  That is to say, the order of their DNA sequences can be slightly different.

The molecular tools used to cut DNa are called restriction enzymes.  There are many different types of restriction enzymes to recognize many different sequences.  This allows some flexibility in where the DNA can be cut.  The tools break the structure of the DNA molecule in a very specific way, not unlike cutting a string with scissors. The enzymes used to paste DNA are called ligases.  The enzyme will take two broken ends and link them together chemically, as if they had always been part of the same molecule.

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