In recombinant dna experiments, what is used to cut pieces of dna and what joins the resulting fragments to form recombinant dna

DNA fragments are cut out restriction enzymes (restriction endonucleases) and then joined together using enzymes called DNA ligases.

Restriction enzymes are enzymes which recognize target sequences (recognition sites) and cuts DNA at or near those sequences.

DNA ligase is an enzyme that connects the gap between the molecules (if they have matching ends).

an active site is a region that is present on an enzyme where the reactants or the substrate molecules we can say bind and experience a chemical reaction. the substrate is basically a reactant whose concentration is changing and that is converting into a product after binding at the active site of an enzyme