Why is it good to close a restriction enzyme tube quickly?

Correct answer: To reduce temperature exposure and contamination

The direct answer is A: closing the restriction-enzyme tube quickly reduces unnecessary temperature exposure and the chance of contamination. These enzymes are usually stored cold, and repeated warming, prolonged time outside the recommended temperature, or evaporation can reduce their performance. Step by step: remove the tube briefly; take the required amount with a clean technique; return it promptly to the proper storage condition; close it firmly; this limits warming, contamination, and loss of sample. A is correct. B is wrong because quick closing does not burn DNA. C is wrong because tube handling does not stain a gel. D is wrong because it does not make protein. The exact stability depends on the enzyme and storage instructions, so good practice is to follow the supplier’s guidance and avoid repeated freeze-thaw cycles. Memory cue: “cold, clean, closed.”