The basic elements that make up a cell are: O, C, H, N, Si, K, Ca, P, Mg, of which O, C, H, N account for more than 90%. Cytochemicals can be divided into two categories: inorganic and organic. In inorganic matter, water is the most important component, accounting for about 75% -80% of the total content of cellular material.
1. Water and inorganic salts
(1) Water is the most basic substance of protoplasm
Not only is water the most abundant in cells, but because it has some unique physical and chemical properties, it plays a key role in the origin of life and the formation of ordered cells. It can be said that there is no life without water. Water exists in two forms in cells: one is free water, which accounts for about 95%; the other is bound water, which is bound to proteins through hydrogen bonds or other bonds, which accounts for about 4% to 5%. As the cell grows and ages, the water content of the cell gradually decreases, but the water content of the living cell is not less than 75%.
The main functions of water in cells are to dissolve inorganic substances, regulate temperature, participate in enzyme reactions, participate in material metabolism and form ordered cells. The reason why water has so many important functions is inseparable from the unique properties of water.
1. Water molecules are dipoles
From the chemical structure point of view, water molecules seem to be very simple, only composed of 2 hydrogen atoms and 1 oxygen atom (H2O). However, the charge distribution in water molecules is asymmetric, showing positive charge on one side and negative charge on the other side, thus showing electrical polarity, which is a typical dipole (Figure 3-31). Because of this characteristic, water molecules can combine with both positive and negative charges in proteins. Each amino acid in protein can bind an average of 2.6 water molecules.
Because water molecules have polarity and produce electrostatic effects, it is a good solvent for some ionic substances (such as inorganic salts).
2. Hydrogen bonds can be formed between water molecules
Since water molecules are dipoles, weak hydrogen bonds can be established between water molecules and between water molecules and other polar molecules. Each oxygen atom in water can form two hydrogen bonds with the hydrogen atoms of two other water molecules. The hydrogen bonding force is very weak, so the hydrogen bonding between molecules is often in the process of breaking and rebuilding.
3. Water molecules can dissociate into ions
Water molecules can dissociate into hydroxide ions (OH-) and hydrogen ions (H +). Under standard conditions, there are always a small number of water molecules dissociated into ions, about 107mol / L water molecules dissociated, which is equivalent to 2 out of every 109 water molecules. However, the electrolysis of water molecules is not stable, and is always in a dynamic balance between the conversion of molecules and ions.
(2) Inorganic salt
The content of inorganic salts in the cells is very small, accounting for about 1% of the total cell weight. Salt dissociates into ions in cells, and the ion concentration has many important functions in addition to regulating osmotic pressure and maintaining acid-base balance.
The main anions are Cl —, PO 4 — and HCO 3 —, among which phosphate ions are the most important in cell metabolic activities: ①plays a key role in the energy metabolism of various cells; The composition of phosphorylated sugar; ③ adjust the acid-base balance, buffer the pH of blood and tissue fluid.
The main cations are: Na +, K +, Ca2 +, Mg2 +, Fe2 +, Fe3 +, Mn2 +, Cu2 +, Co2 +, Mo2 +.
Table 3-4 The role of cations in cells
The role of ion species in cells
Composition of Fe2 + or Fe3 + hemoglobin, cytochrome, peroxidase and ferritin
Na + maintains membrane potential
K + is involved in protein synthesis and certain enzymatic synthesis
Mg2 + chlorophyll, phosphatase, Na'—K 'pump
Mn2 + peptidase
Cu2 + tyrosinase, ascorbate oxidase
Co2 + peptidase
Mo2 + nitrate reductase, xanthine oxidase
Ca2 +, calmodulin, actin, ATPase
2. Organic molecules of cells
There are thousands of organic substances in the cell, accounting for more than 90% of the dry weight of the cell. They are mainly composed of carbon, hydrogen, oxygen, nitrogen and other elements. Organic matter is mainly composed of four types of molecules, namely proteins, nucleic acids, lipids and sugars. These molecules account for more than 90% of the dry weight of cells.
(1) Protein
In life activities, proteins are extremely important macromolecules. Almost all kinds of life activities are related to the existence of proteins. Protein is not only the main structural component of the cell, but more importantly, the biological proprietary catalyst-the enzyme is a protein, so the cell's metabolic activity cannot be separated from the protein. A cell contains about 104 kinds of proteins, and the number of molecules reaches 1011.
(2) Nucleic acid
Nucleic acid is the carrier molecule of biological genetic information. All living things contain nucleic acid. Nucleic acids are large molecules made from the polymerization of nucleotide monomers. Nucleic acids can be divided into ribonucleic acid RNA and deoxyribonucleic acid DNA. When the temperature rises to a certain height, the double-stranded DNA is dissociated into single strands, called denaturation or melting. This temperature is called melting temperature (Tm). DNAs with different base compositions have different melting temperatures. DNAs with many G-C pairs (3 hydrogen bonds) have high Tm; those with many A-T pairs (2 hydrogen bonds) have low Tm. When the temperature drops below a certain temperature, the complementary single strand of denatured DNA can restore the double helix structure of the DNA by forming hydrogen bonds between the paired bases. This process is called renaturation or annealing.
There are three main conformations of DNA (Figure 3-35):
B-DNA: right-handed spiral model proposed by Watson & Click, with 10 bases per turn, helix twist angle of 36 degrees, pitch 34A, helix rise value of each base pair is 3.4A, base inclination is -2 degrees .
A-DNA: It is a right-handed helix, with 10.9 bases per turn, a torsion angle of 33 degrees, a pitch of 32A, a helix ascent of each base pair of 2.9A, and a base inclination of 13 degrees.
Z-DNA: a left-handed helix, with 12 bases per turn, helix twist angles of -51 degrees (G-C) and -9 degrees (C-G), pitch 46A, and helix rise value of each base pair It is 3.5A (G-C) and 4.1A (C-G), the base inclination is 9 degrees.
(3) Sugar
The sugars in cells include both monosaccharides and polysaccharides. Monosaccharides in cells exist as raw materials for energy and sugar-related compounds. The important monosaccharides are five-carbon sugars (pentoses) and six-carbon sugars (hexoses), of which the most important five-carbon sugar is ribose and the most important six-carbon sugar is glucose. Glucose is not only the key monosaccharide of energy metabolism, but also the main monomer constituting polysaccharides.
Polysaccharides play a major role in cell structural components. Polysaccharides in cells can be basically divided into two categories: one is nutrient reserve polysaccharides; the other is structural polysaccharides. There are two main types of polysaccharides used as food reserves, starch in plant cells and glycogen in animal cells. The structural polysaccharides in eukaryotic cells are mainly cellulose and chitin.
(4) Lipids
Lipids include: fatty acids, neutral fats, steroids, waxes, glycerol phosphates, sphingolipids, glycolipids, carotenoids, etc. Lipid compounds are difficult to dissolve in water, but easily soluble in non-polar organic solvents.
1. Neutral fat
â‘ Glycerin: It is a triglyceride formed by combining the carboxyl group of fatty acid with the hydroxyl group of glycerin. Glycerides are the main storage form of fat in animals and plants. When carbohydrates, proteins or lipids are in excess, they can be converted into glycerides and stored. Glycerin is an energy substance, which can release twice as much energy as sugar or protein during oxidation. When nutrition is lacking, it is necessary to use glycerides to provide energy.
â‘¡Wax: esterification of fatty acid with ethanol to form wax (such as beeswax). The hydrocarbon chain of wax is very long and its melting point is higher than that of glyceride. The cells do not contain wax, but some cells can secrete wax. Such as: wax film secreted by plant epidermal cells; wax glands of homoptera insects, such as cerumen glands of the external auditory meatus of higher animals.
2. Phospholipids
Phospholipids are essential for the structure and metabolism of cells. They are the basic components of biofilms and are participants in many metabolic pathways. Divided into two major categories of glycerophospholipid and sphingomyelin.
3. glycolipid
Glycolipids are also components of cell membranes, which are related to cell recognition and surface antigenicity.
4. Terpenes and steroids
Both of these compounds are derivatives of isoprene and neither contain fatty acids.
The main terpenoids in organisms are carotene and vitamins A, E, and K. There is also a polyterpene phosphate, which is a carrier of glycosyltransferases in the cytoplasm.
Steroids (steroids) compounds, also known as steroids, in which cholesterol is a component of the membrane. Other steroids are hormones, such as female hormones, male hormones, and adrenal hormones.
3. Enzymes and biocatalysts
(1) Enzyme
Enzymes are proteinaceous catalysts. Their main role is to reduce the activation energy of chemical reactions, increasing the probability of reactant molecules crossing the activation energy barrier and completing the reaction. The mechanism of action of the enzyme is that the enzyme and the substrate temporarily combine during the reaction to form an enzyme-substrate activation complex. The demand for activation energy of this complex is low, so the number of complex molecules crossing the activation energy barrier per unit time is greater than that of simple molecules. After the reaction is completed, the enzyme molecule is immediately released from the enzyme-substrate complex.
The main characteristics of the enzyme are: high efficiency catalytic ability, high specificity and adjustability; require suitable pH and temperature; only catalyze thermodynamically allowed reactions, both have positive and negative reactions catalytic ability, in essence, can accelerate the reaction Speed ​​of balance.
Some enzymes require a non-protein cofactor to be active. The cofactor can be a complex organic molecule, a metal ion, or both. The complete protein-cofactor complex is called holoenzyme. The whole enzyme removes the cofactor, and the remaining protein part is called apoenzyme.
(2) RNA catalyst
T. Cech 1982 found that Tetrahymena (Tetrahymena) rRNA precursors can self-process without the involvement of any protein to produce mature rRNA products. This processing method is called self splicing. Later, it was discovered that this cut RNA intron sequence, like enzymes, also has catalytic activity. This RNA sequence is about 400 nucleotides long and can be folded into a complex structure on the surface. It can also be combined with another RNA molecule to cut it at a localized point, so this RNA sequence with catalytic activity is called Ribozyme. Later, it was discovered that RNA with catalytic activity is not only present in Tetrahymena, but is widespread in prokaryotes and eukaryotes. A typical example of ribosomal peptidyl transferase, in the past it has been thought that the peptide chain synthesis is the role of the protein in the ribosome, but in fact the component with peptidyl transferase activity and catalyze the formation of peptide bonds is RNA, not protein The protein in the ribosome only serves as a scaffold.
A training chair is a seat designed specifically for activities such as training and meetings. It has the characteristics of comfort, durability, and ease of movement, which can meet the needs of different groups of people. Training chairs can be classified into various categories based on material, structure, function, and other aspects. Below will be a brief introduction to the classification of training chairs.
1. Material classification
The materials of the training chair mainly include metal, plastic, and fabric. Metal training chairs typically have strong stability and durability, making them suitable for long-term meetings or training activities. The training chair made of plastic material has the characteristics of lightweight and easy to clean, making it easy to arrange the meeting site at any time and suitable for use in multifunctional halls and other places. The training chair made of fabric has a comfortable sitting experience and good breathability, making it suitable for long-term meetings or training activities.
2. Structural classification
The structure of training chairs mainly includes single chairs, linked chairs, and foldable chairs. Single chairs are the most common training chairs, with each seat being independent and adjustable as needed. Chainage refers to the connection of multiple seats together, usually in the form of one or more rows, suitable for use in large training venues. Stackable chairs are training chairs that can be folded and stacked, saving space and facilitating storage and handling.
3. Functional classification
The main functions of the training chair are adjustable, rotatable, foldable, and storable. The adjustable training chair can adjust the height and angle according to personal needs, providing a more comfortable sitting posture. The rotatable training chair can rotate 360 degrees, facilitating communication and interaction with people around it. The foldable training chair can be conveniently stored and transported, making it suitable for use in multifunctional halls and other places. The training chair that can store items is designed with storage space below or behind the chair, making it convenient to store items such as stationery and documents.
In summary, the classification of training chairs mainly includes material classification, structural classification, functional classification, etc. Choosing a suitable training chair can provide a better user experience and improve the effectiveness of training and meetings.
Meeting Chair,,Foldable Chair,Customized Chair
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