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Restriction enzymes, commonly referred to as molecular scissors, are invaluable tools in the field of genetic engineering. These naturally occurring enzymes are derived from bacteria, where they serve as a defense mechanism against viral DNA. Their specificity for particular DNA sequences allows them to cleave the DNA at precise locations, referred to as restriction sites. Each restriction enzyme has its unique sequence it recognizes, usually within 4 to 8 base pairs long.

When these enzymes are used in DNA cloning, they create cuts that generate 'sticky ends' or 'blunt ends'. Sticky ends have overhanging sequences that can base pair with complementary sequences on another piece of DNA cut by the same enzyme. This property is critical when attaching a DNA fragment of interest into a vector, like a plasmid, because it helps to ensure that the fragment is inserted in the correct orientation and location.

Cloning vectors are DNA molecules that can carry a foreign DNA fragment to be cloned. Acting as delivery vehicles, they are fundamental to the cloning process. The most popular vectors are plasmids, which are small, circular DNA molecules distinct from the bacterial chromosome and capable of independent replication.

Specific features of cloning vectors facilitate the cloning process. They often include a 'multiple cloning site', a region with numerous restriction sites allowing for the insertion of DNA fragments. Additionally, they generally carry 'selectable marker genes' that confer resistance to antibiotics. This is exploited to maintain and identify cells that have successfully incorporated the recombinant DNA. Vectors may also have 'reporter genes', coding for easily observed characteristics, such as fluorescence, to further aid in the identification of recombinant clones.

Recombinant DNA technology involves the combination of DNA molecules from different sources into one molecule to create a new genetic combination. This powerful technology underpins genetic engineering and has vast applications ranging from medicine to agriculture. The resultant molecule, known as recombinant DNA, is then introduced into a host organism to produce new genetic combinations.

The creation of recombinant DNA typically involves cutting DNA from a donor species with restriction enzymes and inserting it into a vector that has been cut with the same enzymes. This ensures compatibility of the ends, allowing the donor DNA to be ligated seamlessly into the vector. Once inside a host cell, the recombinant DNA can replicate and, in some cases, express the genes it carries, leading to the production of new proteins.

Plasmids are naturally occurring, extrachromosomal DNA molecules found in bacterial cells, and they are also present in some eukaryotes. Their ability to replicate independently from the main bacterial chromosome makes them an invaluable tool in genetic engineering. In the context of DNA cloning, plasmids are engineered to be cloning vectors.

Plasmids used in cloning often have a high copy number, meaning each bacterium can contain multiple copies of the plasmid, leading to substantial DNA amplification. Additionally, because plasmids are transferred between bacteria through a process called conjugation, they can spread recombinant DNA throughout a bacterial population. This feature is instrumental in the mass production of genetic material for research, pharmaceuticals, and other biotechnological applications.