What Does a DNA Scientist Do?

DNA is deoxyribonucleic acid (abbreviation of Deoxyribonucleic acid in English), which is the main component of chromosomes and also the main genetic material.

With the rapid development of molecular biotechnology, DNA molecular identification has been widely used in various fields of life sciences. DNA molecular identification technology has been more and more applied to the identification of traditional Chinese medicine.It can be used to solve certain problems of traditional Chinese medicine, especially animal traditional Chinese medicine identification.It has the characteristics of high accuracy and good reproducibility. Using the DNA molecule as a direct carrier of genetic information as the basis for identification, the identification of Chinese medicine varieties is more in-depth and objective. For example, the identification of tortoise shells, tortoise shells, snakes, deer, toads and other medicinal materials has overcome the deficiency of identifying such medicinal materials based on morphology, microscopic characteristics and physical and chemical methods to a certain extent. DNA molecular identification of snake medicinal materials such as black snake and viper has been included in the 2015 edition of the Chinese Pharmacopoeia.

In addition to DNA molecular identification, there are still biological animal imprinting techniques to identify animal traditional Chinese medicine. It is mainly used that different species of animals contain their own specific proteins and have immunospecificity, which can be used for identification and analysis of animal drugs with relatively close relationships. Convection immunoelectrophoresis and agar immunodiffusion can accurately detect bones of tigers, leopards, pheasants, cats, cattle, pigs, etc., and the purpose of identifying fakes has been achieved ^[1]

In the 1940s and 1950s, scientists have known that DNA molecules are a kind of high molecular compound composed of 4 kinds of deoxynucleotides. However, why a DNA molecule composed of only four kinds of deoxynucleotides can become genetic material is still confused. For this reason, many scientists have invested in the study of the molecular structure of DNA. In 1953, based on previous work, Watson and Crick proposed the famous double-helix structure model of DNA molecules, which laid the structural foundation for the complex functions of genes. Genetic research has made rapid progress.

DNA is a double-helix biological macromolecule.Its basic unit is deoxy-nucleotide.Each single nucleotide consists of three simple compounds: phosphate, deoxyribose and base. One molecule each. There are two major types of bases, purines and pyrimidines. The main purines are adenine (A) and guanine (G). The main pyrimidines are cytosine (C) and thymine (T). These purines and pyrimidines are nitrogenous. Heterocyclic compounds, called nitrogenous bases ^[2]

Sometimes referred to as "genetic microparticles", because during reproduction, parents copy half of their own DNA to

The discovery of DNA structure is one of the most legendary "chapters" in the history of science. Discovering the structure of DNA is an epoch-making achievement, but the method of discovering it is model construction. The model construction method is like the "patch-up" method of children's jigsaw puzzles. And the best performers in this "patch-up" were Watson and Crick.

On April 6, 1928, Watson was born in Chicago, USA. He graduated from the University of Chicago at the age of 16 with a bachelor's degree in zoology and began to show his talent in biology. After getting a PhD at the age of 22, Watson came to the Cavendish Laboratory at the University of Cambridge, England, and met Crick, who had already worked here, and began a legendary collaboration between the two. Crick was born in Northampton, England on June 8, 1916. He graduated from the University of London at the age of 21. After the end of World War II, he came to the Cavendish Laboratory in Cambridge. Like Watson, Crick had a strong interest in DNA and switched from physics to biology.

At that time, people already knew that DNA was a long and slender polymer compound composed of a series of deoxynucleotide chains. Deoxynucleotides were composed of deoxyribose, phosphoric acid, and nitrogen-containing bases. There were four kinds of bases. They are adenine (A), guanine (G), cytosine (C) and thymine (T). In 1951, many scientists launched a competition for the study of the structure of DNA. At the time there were two well-known research groups on DNA molecules. One was a research group led by the famous physicist Wilkins and chemist Franklin. They used X-ray diffraction to study the structure of DNA. A research group from the California Institute of Technology, headed by the well-known chemist Pauling, mainly uses model construction to study the structure of DNA, and has used this method to discover the protein a helix.

In February 1951, Wilkins will take a very beautiful X-ray diffraction picture of DNA taken by Franklin

X-ray diffraction of DNA

At the conference on the structure of biological macromolecules held in Italy, Watson, who has always had a strong interest in DNA, saw this picture, and was so excited that he couldn't say anything. His heart was pounding, and based on this picture, he concluded that DNA The structure is a spiral body. He made up his mind to make a DNA model. He told his collaborator Crick of this idea, which was approved by Crick.

Watson and Crick's work on modeling the molecular structure of DNA began in the fall of 1951. They used a model construction method, imitating the method of the famous chemist Pauling to build a protein alpha helix model, and based on crystallographic data, they used paper and iron wires with deoxynucleotides.

They built one model after another, and all were rejected. But Watson insisted that the DNA molecule could be a double-stranded structure. Because things in nature are many in pairs, the chromosomes in cells are also paired. After that, they completed a double helix structure in which deoxyribose and phosphoric acid are alternately arranged as the basic skeleton and the bases are arranged outside, and a basic skeleton with deoxyribose and phosphate alternately arranged as the basic skeleton, with the bases arranged inward and the same type of base pairing Double helix structure.

In 1952, when the biochemist Chagaff visited Cambridge University, he reported the results of his analysis of human, pig, cattle, sheep, bacteria and yeast. Chagaff's results show that although the numbers and relative proportions of the four kinds of deoxynucleotides are very different between the DNAs of different organisms, no matter which kind of DNA, there are A = T and G = C. This is called the "Chargaff's Law" of DNA chemistry. In July 1952, when Chagaf visited Cavendish Laboratory, he explained to Crick the rule of A: T = G: C = 1: 1. Later, Crick's friend and theoretical chemist Griffith calculated that among the four deoxynucleotides of DNA, A must be bonded to T, and G must be bonded to C. This is consistent with the completion of Chargaff's Law. Subsequently, Pauling's former colleague Dono told Watson that the AT and GC pairing was maintained by hydrogen bonding. The above work has become the basis of the A-T paired and G = C paired structures in the DNA molecular model of Watson and Crick.

So far, the DNA model has emerged. On February 28, Watson made a model of four bases from cardboard, glued the cardboard to the backbone and paired them towards the center. Crick immediately pointed out that only the two single strands can be reversed to make the bases perfectly paired. It coincides with the X-ray diffraction data. A complete DNA molecular structure model was completed on March 7, 1953. According to this model, the DNA molecule is a double helix structure, and each helix unit contains 10 bases and has a length of 34 Angstroms (1 Angstrom = 10-10 meters). The spiral diameter is 20 angstroms. On April 15, Watson and Creek's first paper on the model was published in the journal Nature.

The discovery of the double helix structure model of DNA molecules is a milestone in the history of biology. It provides a structural explanation for DNA replication, makes people no longer doubt the material basis of DNA as a gene, and lays the foundation for molecular genetics. . The scientific impact of the DNA double helix model is profound.

DNA molecular structure

A DNA molecule is a long chain connected by four kinds of deoxynucleotides, and these four kinds of deoxynucleotides each contain four bases: A, T, C, and G.