Why carbohydrates are considered important information molecules

As one of the four major molecules of living organisms, the physiological role of carbohydrates has long been considered to be only the energy supply substances of the body and the structural substances that make up plants. Since the 1960s, scientists have discovered that cell surfaces are densely packed with sugar chains, which are oligosaccharide molecules attached to proteins and lipid macromolecules. It was not until the 70s of the 20th century, with the development of molecular biology, that some important physiological functions of sugar that were little known were discovered.

Sugars have multiple hydroxyl groups, glycosidic bonds are divided into configurations, and the linkage of monosaccharides may produce a large number of isomers, therefore, the sugar chain structure contains very rich biological language information, which is a high-density information carrier.

Cells are the basic unit of living organisms, and a wide variety of cells form various tissues, all of which are covered with a glycocoat on their surface. Sugars often form covalent complexes with proteins—glycoproteins. Many enzymes, immunoglobulins, carrier proteins, hormones, toxins, lectins, and most of the proteins are glycoproteins.

In glycoproteins, the length and structure of various glycoprotein sugar chains, and the number of sugar chains are very different, so the sugar content is also very different. For example, the ovalbumin molecule contains a sugar chain; The submandibular mucin molecule of sheep contains 800 oligosaccharide chains, and the sugar content of pyrogen protein is less than 1%; The sugar content of soluble blood group substances is up to 85%.

The mutual adhesion, mutual recognition, interaction, mutual restriction and regulation of cells are all related to the glycan chain of glycoproteins. A large number of studies have shown that the generation of various intricate life phenomena and the formation of diseases include many molecular changes and complex metabolic processes, among which the glycoprotein glycan chain plays an important role in fertilization, occurrence, development, differentiation, inflammation and autoimmune diseases, abnormal proliferation and metastasis of cancer cells, pathogen infection, plant-pathogen interaction, and symbiosis between leguminous plants and rhizobia.

Probably because the DNA genetic material is made up of ribose.

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The signals received by biological cells can be both physical and chemical, but the most widespread signals in communication between organisms and cells are chemical signals.

From the perspective of chemical structure, cell signaling molecules include: proteins, gas molecules (NO) and lipids, etc., and their common characteristics are: specificity, can only bind to specific receptors High efficiency, a few molecules can have obvious biological effects; It can be inactivated, and can be degraded or modified to lose activity after completing information transmission, ensuring the integrity of information transmission and the cells from fatigue.

From the perspective of production and mode of action, it can be divided into hormones, neurotransmitters and lymphokines.

From the perspective of solubility, it can be divided into two categories: fat-soluble and water-soluble. Fat-soluble signaling molecules, such as thyroid hormones, can directly penetrate the membrane into target cells and bind to intracellular receptors to form hormone-receptor complexes that regulate gene expression.

Water-soluble signaling molecules, such as neurotransmitters, lymphokines, and water-soluble hormones, cannot cross the target cell membrane, but can only bind to the membrane receptor and cause the cell through the signal conversion mechanism through intracellular messengers or the enzymatic activity that activates the membrane receptor.

of response responses.

In the case of glycoproteins, it should be ...... receiving molecules