Final answer:
Restriction enzymes restrict the multiplication of bacteriophage in bacteria by specifically recognizing and cleaving DNA at particular sequences, thus functioning as a defense mechanism and a tool in molecular biology.
Step-by-step explanation:
‘Restriction enzymes’ are called so because they restrict the multiplication of bacteriophage in bacteria by recognizing and cutting DNA only at specific positions. These enzymes are highly specific, recognizing short palindromic sequences in the DNA, to which they bind and then cleave the phosphodiester bonds within the DNA at precise locations. This activity ultimately hinders the proliferation of invading bacteriophages by destroying their DNA. Moreover, the recognition sites for restriction enzymes are often methylated in the bacteria's own DNA as a protective mechanism against self-digestion; foreign DNA lacking this methylation is then subject to cleavage by these enzymes.
Additionally, restriction enzymes are widely used in molecular biology and recombinant DNA technology as tools for cutting DNA at specific sequences to facilitate gene cloning and DNA analysis. They have been instrumental in developing techniques such as DNA fingerprinting and the creation of recombinant DNA by cleaving at their target recognition sites with extreme specificity.