1.2.1 The structure of DNA

A nucleic acid is a chemical compound which is nucleotides' chain. A nucleotide is consists of a phosphoric acid, deoxyribose and a pair of purine bases or pyrimidine bases. The nucleic asid is diviede into two parts, the DNA and RiboNucleic Acid(RNA). The purine base of the DNA is consists of an adenine and a guanine same as RNA, and the pyrimidine base consists of a cytosine and a thymine. The pyrimidine base of the RNA is different from that of the DNA, and consists of a cytosine and an uracil instead of a thymine. The DNA is the body of a gene and is mainly in a nucleus and forms chromosomes as the nucleoprotein. The structure of the DNA is known as the "double helix structure" discovered by Watson and Crick in 1953.

1.2.2 The nucleotide

The nucleotide of the DNA has an adenine, guanine, cytosine, and thymine as its bases and about RNA, it has an uracil instead of a thymine. Sugar found in the nucleotide of the DNA is a deoxyribose, but that of the RNA is a ribose.

1.2.3 The double helix structure

The double helix structure of the DNA was proposed by Watson and Crick in 1953. Its three-dimensional model has two polynucleotides and they form clockwise helixes around a same axis. From this shape, the structure of the DNA is called "double helix structure". Two polynucleotides face different direction with each other.

Between bases is a shape called "Watson and Crick's base pair", which is a special hydrogen bounding. An adenine forms a base pair always with a thymine and a guanine forms base pair always with a cytosine in the same way. In both cases of A-T base pair and G-C base pair, the distance between carbon atoms of two chains is always same. This relation makes it possible to construct the double helix structure in case of A-T base pair and G-C base pair.

1.2.4 The replication of DNA

Replicating steps of a DNA are such as follows:

The double helix structure unties from the end and it is dvieded into two chains.
Pairs of nucleotides that have complementary bases make hydrogen boundings between bases.
As a result, two double helix structured DNA are generated.

The replication of a DNA has two remarkable features. One is that generated two DNA have same structure. The other is that both generated double helix structures consist of an original DNA chain and a new DNA chain. This way of replication is called "semiconservative replication".

1.3 The compound of DNA and protein

Any kinds of organic compounds in a living body are compounded by oxygen reactions. In case of protein, genetic information of the DNA are replicated to the RNA and they are translated into amino acids and then they are compound as protein. Protein are compound by following steps:

A part of the dobule helix of a DNA is untied and the base arrangement is replicated to messanger RNA(m-RNA).
The m-RNA that has genetic information goes outside of the cytoplasm and join the liposome in which protein are compounded.
The transfer RNA(t-RNA) transfers an amino acid to the m-RNA which is on the liposome.
Moving on the m-RNA, the liposome decodes the base arrangement of m-RNA and compounds it to the t-RNA which has an appropriate base arrangement.
These peptide bonds are repeated and protein which match genetic information are generated. The t-RNA which released an amino acid will transfer a new amino acid again.

1.1 The body of a gene

1.2 The structure of DNA

1.3 The DNA and compound of protein

(c) 1994-95 Chiyokura Laboratory, Keio University Shonan Fujisawa Campus
and the Information-technology Promotion Agency, Japan(IPA).

Modificado em: 18-01-1999