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Q: What is molecular cloning?

     The word cloning refers to the fact that the method involves the replication of one molecule to produce a population of cells having identical DNA molecules. Molecular cloning generally uses DNA sequences from two different organisms/cells: the species that is the source of the DNA to be cloned, and the species that will serve as the living host for replication of the specific sequence of DNA from the first organism/cell.The specific DNA sequence of our interest is isolated from a cell, by using restriction enzymes to cut the DNA into fragments. These fragment DNAs are inserted into a vector DNA (a circular DNA called plasmid DNA), to make the recombinant DNA.             

    The recombinant DNA carries, the specific DNA sequence of our to the host organism. Because they contain foreign DNA fragments, these are transgenic or genetically modified microorganisms (GMO).his process takes advantage of the fact that a single bacterial cell can be induced to take up and replicate a single recombinant DNA molecule. This single cell can then be expanded exponentially to generate a large amount of bacteria, each of which contain copies of the original recombinant molecule. Thus, both the resulting bacterial population, and the recombinant DNA molecule, are commonly referred to as "clones". Strictly speaking, recombinant DNA refers to DNA molecules, while molecular cloning refers to the experimental methods used to assemble them.

 This molecular cloning is pictorially represented as follows.

For further reference: The book "The basic principles of Gene cloning and DNA analysis" by T A Brown would be helpful