There are a large number of Restriction Endonucleases available for scientific research, but they are all kept in freezers like this one until it's time to use them. Concentrated stocks of the enzymes are stored in a solution which contains a high level of glycerol to prevent the water in the tube from freezing and ruining the enzyme. Because the enzyme stock is concenrated, one small microcentrifuge tube can hold enough enzyme for potentially dozens of Restriction Digests. And because the tubes are so small, many different RE's can be kept in a small space, like the top two red boxes seen above.

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