DNA Structure and Genetic Engineering Applications

Chemical Language and Genetic Instruction

Genes are DNA molecules; these are carriers of information necessary for the development of a cell or an individual. They are the only molecules capable of self-replicating (making copies of themselves). They perform their function due to the existence of the genetic code. Reading this code, or its expression, results in the synthesis of specific proteins. Genes can be deliberately manipulated by genetic engineering techniques. Genetic manipulation has a wide range of applications, including obtaining drugs, vaccines, disease diagnosis, and gene therapy.

DNA: The Molecule of Heredity

Genes are the carriers of biological information and, therefore, are located within all cells. However, their location was unknown until it was discovered that the number of chromosomes in sex cells is half of that which exists in other cells. Thus, it was rightly thought that genes were contained in the chromosomes. However, it had to be determined which of the molecules that form the chromosomes (DNA or protein) was the molecule of heredity.

At present, it is known that a gene consists of a molecule called DNA (deoxyribonucleic acid). This molecule is the carrier of information that gives a cell and a body its biological characteristics. Everything that an organism is depends on its DNA.

The Simple Chain Structure

The DNA molecule is formed by the union of many molecules called nucleotides. Each nucleotide consists of three smaller molecules: deoxyribose, a nitrogenous base, and phosphoric acid. DNA nucleotides differ in the type of nitrogenous base. There are four types:

• Adenine (A)
• Cytosine (C)
• Thymine (T)
• Guanine (G)

The nucleotide binding results in a long chain of alternating deoxyribose and phosphoric acids. The nitrogenous bases are hanging from the deoxyribose.

The Double Chain and Helix

1. DNA consists of two chains of nucleotides.
2. The double chain is arranged in the form of a double helix.
3. The union of the two chains of nucleotides is possible because the facing nucleobases are linked.
4. The union between the bases of both chains is not random, but always made according to this pattern: adenine-thymine and cytosine-guanine; it is said that one base is complementary to the other.
5. The packing of DNA within the cell nucleus is immense: in a human cell, there are 4 meters of DNA bound within a nuclear space of just 5 µm in diameter.