what is molecular cloning?

Answer 1

Molecular cloning or expression cloning, is one of the most basic techniques of molecular biology to study protein function.
In this technique, DNA coding for a protein of interest is inserted (using PCR and/or restriction enzymes) into a plasmid (known as an expression vector). The cloned DNA is normally only the "coding" portion of the gene of interest, in which all the introns have been removed, and derives from the reverse tanscriptase of the mRNA.
The expression vector may have special promoter elements to drive production of the protein of interest, and may also have antibiotic resistance markers to help follow the plasmid.
The obtained plasmid is normally propagated using an Escherichia coli strain (famous ones are DH5alpha and JM109) which can be grown in special media (LB medium) in big quantities, and then the plasmid can be purified.
There are plasmids for protein expression in bacteria, in yeast, in insect cells (Sf9) and in mammalian cells (cultured cells). The difference between these plasmids is what promoter (regulatory sequence) is regulating the expression of the protein of interest as the transcription factors that bind to the promoter are species specific.

Hope it helps, but the field is really vast...

Answer 2

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RE:
what is molecular cloning?

Answer 3

The molecular analysis of DNA has been made possible by the cloning of DNA. The two molecules that are required for cloning are the DNA to be cloned and a cloning vector.
Cloning vector - a DNA molecule that carries foreign DNA into a host cell, replicates inside a bacterial (or yeast) cell and produces many copies of itself and the foreign DNA

Three features of all cloning vectors


sequences that permit the propagation of itself in bacteria (or in yeast for YACs)
a cloning site to insert foreign DNA; the most versatile vectors contain a site that can be cut by many restriction enzymes
a method of selecting for bacteria (or yeast for YACs) containing a vector with foreign DNA; uually accomplished by selectable markers for drug resistance
Types of Cloning Vectors

Plasmid - an extrachromosomal circular DNA molecule that autonomously replicates inside the bacterial cell; cloning limit: 100 to 10,000 base pairs or 0.1-10 kilobases (kb)
Phage - derivatives of bacteriophage lambda; linear DNA molecules, whose region can be replaced with foreign DNA without disrupting its life cycle; cloning limit: 8-20 kb
Cosmids - an extrachromosomal circular DNA molecule that combines features of plasmids and phage; cloning limit - 35-50 kb
Bacterial Artificial Chromosomes (BAC) - based on bacterial mini-F plasmids. cloning limit: 75-300 kb
Yeast Artificial Chromosomes (YAC) - an artificial chromosome that contains telomeres, origin of replication, a yeast centromere, and a selectable marker for identification in yeast cells; cloning limit: 100-1000 kb
General Steps of Cloning with Any Vector

prepare the vector and DNA to be cloned by digestion with restriction enzymes to generate complementary ends
ligate the foreign DNA into the vector with the enzyme DNA ligase
introduce the DNA into bacterial cells (or yeast cells for YACs) by transformation
select cells containing foreign DNA by screening for selectable markers (usually drug resistance)