Stages of Recombinant DNA

Principles of Recombinant DNA

The term recombinant DNA refers to any DNA molecule that has been produced by joining genetic material from two different sources. The term is also used to describe the process by which this type of DNA is produced. That process usually involves the insertion of a gene from one organism into the genome of a different organism, usually of a different species. For example, a human gene might be inserted into bacterial DNA, forming a new, mixed kind of bacterial DNA sometimes called chimeric DNA. That name comes from the mythical Greek monster called the chimera, which had the head of a lion, the body of a goat, and the tail of a serpent (Dhar, 287-296).

Recombinant DNA is a form of genetic engineering, the process by which a molecule of DNA has been artificially altered by any means whatsoever. Recombinant DNA and genetic engineering are both forms of an even more general process known as biotechnology. Biotechnology has been defined in a number of ways. The definition adopted by the Convention on Biological Diversity, an important international agreement, is "any technological application that uses biological systems, living organisms, or derivatives thereof, to make or modify products or processes for specific use." DNA (the acronym for deoxyribonucleic acid) is a large molecule having roughly the shape of two spaghetti strands wrapped around each other. The chemical structures for the three kinds of chemical units found in DNA are shown below. These units are a sugar (deoxyribose), a phosphate group, and four nitrogen bases: adenine, cytosine, guanine, or thymine. The four bases are usually represented by capital letters: A, C, G, and T, respectively.

Structure of Phosphate and Deoxyribose

Four Bases of DNA

The backbone of the DNA molecule is a chain of sugar and phosphate molecules, as shown in the diagram below. Attached to each sugar unit in the chain is one of the four nitrogen bases. The combination of a sugar unit bonded to a nitrogen base is called a nucleoside. The three-membered unit consisting of a sugar, phosphate group, and nitrogen base is known as a nucleotide.

Backbone of the DNA Molecule

A complete DNA molecule is a dimer, a molecule that consists of two similar units called monomers. Those units are extended strands of nucleotides joined to each other in a shape somewhat like that of a ladder. The two strands that make up a DNA molecule in turn are held together loosely by hydrogen bonds between adjacent nitrogen bases on opposite DNA strands.

The DNA dimer has a three-dimensional form, produced when the two strands twist around each other in a form known as an a-helix (alpha-helix), like that shown in the diagram below.

Structure of DNA

DNA is the "mastermind" of a living cell. It carries the instructions that supervise all of the biochemical changes that take place during growth, development, differentiation, metabolism, and other processes that take place in cells. It also carries the genetic information that organisms pass on to their progeny during the process of ...