My textbook states: “In order to cut the DNA with restriction enzymes, it needs to be in pure form, free from other macromolecules. Therefore DNA isolated from other chemicals of the protoplasm like carbohydrates, lipids and proteins via techniques of DNA isolation.” My question is, why does DNA need to be alone? Won’t restriction enzymes work if there were a DNA molecule in a sugar solution? I understand that the DNA has to be freed from cell membranes and walls for restriction enzymes reach the DNA but how does the presence of other macromolecules hinder DNA’s digestion of a restriction enzyme?
Some other macromolecules or other solutes may be present that could interfere with the affinity of the restriction enzyme. For example, there could be salts that denature or modify the conformation of the enzyme or inhibitors present that may interfere with the enzyme. Hope this helps.