Molecular cloning

Molecular cloning is a set of experimental methods in molecular biology that are used to assemble recombinant DNA molecules and to direct their replication within host organisms. The use of the word cloning refers to the fact that the method involves the replication of one molecule to produce a population of cells with identical DNA molecules. Molecular cloning generally uses DNA sequences from two different organisms: 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 recombinant DNA.

Overview

Molecular cloning methods are central to many contemporary areas of modern biology and medicine. In a conventional molecular cloning experiment, the DNA to be cloned is obtained from an organism of interest, then treated with enzymes in the laboratory to generate smaller DNA fragments. Subsequently, these fragments are then combined with vector DNA to generate recombinant DNA molecules. The recombinant DNA is then introduced into a host organism. This process leads to the amplification of the DNA of interest, and the generation of a large amount of DNA that can be used for further experiments.

Methods

There are several methods of molecular cloning:

• Polymerase chain reaction (PCR) cloning: PCR cloning is a technique where the DNA of interest is amplified using primers with sequences identical to the ends of the vector DNA. The amplified DNA is then directly ligated into the vector.

• Shotgun cloning: In shotgun cloning, DNA is fragmented randomly and cloned into a vector. This is often used in genome sequencing projects.

• TOPO cloning: In TOPO cloning, the vector has overhanging 3' thymidines which pair with overhanging 3' adenines of the insert. This allows for rapid ligation of the insert into the vector.

Applications

Molecular cloning has a wide range of applications. It is used in genetic engineering to create organisms that produce human proteins such as insulin. It is also used in gene therapy to replace defective genes. In addition, it is used in research to study gene function and regulation.

See also

• DNA sequencing
• Genetic recombination
• Molecular biology
• Recombinant DNA

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