Complete collection of detailed data of macromolecules

Macromolecules refer to biological substances with a relative molecular weight of more than 5,000 or even more than one million, such as protein, nucleic acids and polysaccharides. It is closely related to life activities and consists of simple molecular units that are considered as monomers. There are gel-forming substances in the solution. Generally, compounds with relative molecular mass greater than 10000 are called macromolecular compounds or macromolecular compounds. It is composed of many repeated structural units, generally with linear structure and some with dendritic structure. Many substances with important biological functions, such as protein and nucleic acid, belong to this kind of compounds. The basic building block of macromolecular protein is amino acid (AA).

Chinese name: polymer mbth: polymer structure: spatial structure, three-dimensional structure or structural function: determining the spatial position of atoms in crystals Subject: protein crystallography diffraction technology, technical introduction, function, protein crystallography, historical review and brief introduction of diffraction technology: the technology of calculating the three-dimensional structure (also often called spatial structure, three-dimensional structure or conformation) of biological macromolecules from diffraction patterns (direction and intensity of diffraction lines). The main principle is that the diffraction pattern produced by X-ray, neutron beam or electron beam passing through crystals or fibers with ordered biomacromolecules has reciprocal relationship with the arrangement law of atoms in the sample (cross Fourier transform). Action X-ray diffraction technology can accurately determine the spatial position of atoms in crystals, and it is the main technology to study the structure of biological macromolecules so far. Neutron diffraction and electron diffraction technology are used to make up for the shortcomings of X-ray diffraction technology. X-ray diffraction technology of biomacromolecule single crystal was first developed from the study of protein's crystal structure after 1950s, and became a branch of crystallography-protein crystallography in 1970s. Dendritic Macromolecule protein Crystallography Neutron diffraction technique of biomacromolecule single crystal is used to determine the position of hydrogen atom in biomacromolecule, which also belongs to protein Crystallography. X-ray diffraction technology of fibrous biomacromolecules is used to determine some periodic structures of such macromolecules, such as spiral structures. The electron microscope technology based on electron diffraction can measure the two-dimensional image of the size, shape and subunit arrangement of biological macromolecules. The three-dimensional reconstruction technology combining optical diffraction and filtering technology can directly display the low-resolution three-dimensional structure of biological macromolecules. Historical review reveals the background of macromolecules 19 12 German physicist M von Laue predicted that crystals are natural diffraction gratings of X-rays. Since then, British physicists W. H. Boog and W. L. Boog have started X-ray crystallography. Over the past decades, this subject has been continuously developed and perfected, and the crystal and molecular structures of thousands of inorganic and organic compounds have been determined. The structural data it provides has become the basis of modern structural chemistry. However, the traditional methods to analyze the crystal structure of small molecules are not suitable for biological macromolecules with a large number of atoms and complex structures. It was not until 1954 that the British crystallographer and others proposed the isomorphic substitution method of introducing heavy atoms into protein crystals, and it was possible to determine the crystal structure of biological macromolecules. 1960, British crystallographer J.C. Chendru and others first solved a three-dimensional structure of protein molecule-myoglobin, which is composed of 153 amino acids and has a molecular weight of 17500. Fig. 1 [structural model of myoglobin molecule of sperm whale] shows the structural model with a resolution of 2 angstroms. Since then, the research on the crystal structure of biological macromolecules has developed rapidly. By the early 1980s, the three-dimensional structures of nearly 200 biological macromolecules had been determined, which strongly promoted the development of molecular biology. Following the first synthesis of bovine insulin in 1960s, China determined the three-dimensional structure of Trizinc pig insulin in the early 1970s. 1986, China has completed the high-resolution correction of this structure at 1.2 angstrom. Crystal and X-ray diffraction electromagnetic waves travel in a straight line, but in some cases there will be a turning point, which is the diffraction phenomenon. This phenomenon occurs when visible light passes through a pinhole or slit. Because the size of pinhole or slit is the same as the wavelength of visible light, pinhole or slit can be regarded as a point light source, which radiates secondary electromagnetic waves in all directions, or scattered waves. If there are many pinholes or slits arranged in sequence, regular light and dark diffraction patterns will be formed due to the interference of these scattered waves. This is because the phase and amplitude of scattered waves from different parts are different, and the result of their addition is strengthened in some places and weakened in others. These patterns vary with wavelength, pinhole size and arrangement (Figure 2[ Arrangement of Three Pinholes and Their Corresponding Diffraction Patterns]). When X-rays pass through the crystal, the extranuclear electrons of atoms in the crystal can scatter X-rays. If each atom is regarded as a scattering source, because the wavelength of X-ray is the same as the distance between atoms, diffraction will also occur. The crystal structure is characterized by the periodic arrangement of atoms or molecules in the crystal. If a set of abstract geometric points is used to represent the law of periodic repetition, then this arrangement can be expressed as a grid. The three-dimensional lattice structure of the crystal enables the crystal to be divided into countless parallelepiped with the same size and shape, which are called unit cells. It is the basic repeating unit of crystal structure. Each cell contains exactly the same kind, number and arrangement of atoms. It can be inferred that the intensity of diffraction line (also called reflection line) depends on the content of the unit cell, and its direction depends on the wavelength and the size and shape of the unit cell. Determination of crystal structure The diffraction of X-ray, neutron beam and electron beam by crystal follows the same principle of optical transformation as the diffraction of regular pinhole by visible light, that is, the reciprocal image of pinhole or crystal structure (arrangement of atoms in pinhole or crystal) can be obtained by Fourier transform-diffraction spectrum. On the contrary, the inverse transformation of diffraction spectrum is the image of positive space-the arrangement of pinholes or the structure of crystals. In the diffraction of visible light, this inverse transformation can be realized through the focusing process of the lens. But so far, people have not found a way to focus X-ray (or neutron) scattering lines. Therefore, it is impossible to directly observe the image of biological macromolecules. This can only be mathematically calculated by an electronic computer.