protein

Article

January 19, 2022

Protein (蛋白質, cultural language: egg cow) is a macromolecular organic substance that composes the body of an organism in biochemistry. It is also called white matter. Protein The English name protein is derived from the Greek word proteios (important). As can be seen from the Chinese character for protein, dan (蛋) means bird egg, protein is the main component that makes up the white of bird eggs such as eggs. The Chinese word for protein comes from the German word Eiweißstoff (German: Eiweißstoff), which literally means "white matter". Polypeptide is a linkage of numerous amino acids, in which 20 different amino acids are long linked by chemical bonds called peptide bonds. It is only called a protein when various polypeptide chains form a quaternary structure and have unique functions. Although a protein and a polypeptide are technically different molecules, they are sometimes used without distinction in some cases. In general, if the molecular weight is relatively small, it is called a polypeptide, and if the molecular weight is very large, it is called a protein. Proteins play important roles in various forms, such as components in living organisms, catalysis of various chemical reactions in cells (enzymes), and immunity by forming antibodies. The formula is (NH2CHRnCOOH)n. Proteins are digested by the action of a proteolytic enzyme called trypsin. However, soybeans contain a protein called a soytrypsin inhibitor that interferes with the activity of trypsin, so eating raw soybeans is difficult to digest. However, when soybeans are heated, this protein component is denatured and the inhibitory function is lost. In the end, trypsin is activated, making it easier for digestive enzymes to invade. Protein denaturation is caused by physical factors (heating, drying, stirring, pressure, X-rays, ultrasonic waves, vibrations, freezing) or chemical factors (acids, bases) of natural proteins. , urea, organic solvents, heavy metals, surfactants) or the action of enzymes, etc.

Structure

Protein refers to a polypeptide chain that is folded into a unique three-dimensional structure. The structure in which a protein is folded in its natural state is determined by the sequence of amino acids that make up this polypeptide of the protein. Biochemists divide the structure of proteins into four stages. Primary structure: amino acid sequence The structure of a single protein can be changed by the environment and other interacting molecules. This structural modification plays a very important role in the biological functions of proteins such as catalysis, binding to other molecules, and mechanical movement. The primary structure of these linear proteins consists of covalent peptide bonds, which are formed when the protein is synthesized by ribosomes. The secondary, tertiary, and quaternary structures of proteins are maintained by the bonds between the backbone chain and side chain structures that make up the protein. These bonds are divided into non-covalent bonds such as hydrogen bonds, hydrophobic bonds, and ionic bonds, and covalent bonds such as disulfide bonds. Secondary structure: The secondary structure of a protein is formed by the backbone chain. A hydrogen bond is formed between the oxygen atom of the carbonyl group and the hydrogen atom of the amine group of all amino acids in the skeleton, resulting in a thermodynamically stable state (the state with the lowest free energy). At this time, the reason that the secondary structure of the protein mainly takes the shape of an α-helix or a β-sheet is a side saline between two amino acids located right next to each other on the polypeptide.

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