monosaccharide

[d ā n táng]

chemical compound

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Monosaccharides are molecules that can no longer be simply hydrolyzed into smaller sugars. According to the position of carbonyl group aldose (aldose) and Ketose (ketose). According to the number of carbon atoms in the monosaccharide, it can also be divided into triose, butanose, pentose, hexose, heptosaccharide. The most abundant monosaccharides in nature are pentose and hexose^[6] 。 Tricarbonic Glyceraldehyde ； Tetracarbonic Erythrin Sulitose; Pentacarbonic Arabinose 、 Ribose 、 xylose 、 Lysose ； Hexacarbonic glucose 、 mannose 、 fructose 、 Galactose 。 The main monosaccharide in food is hexose (hexose).^[1]

Chinese name: monosaccharide
Foreign name: Monosaccharide
Definition: Non hydrolyzable sugars

Category: Triose , butyl sugar Pentose 、 Hexose etc.
Structure: Ring structure and chain structure
physical property: Colorless crystal, sweet, hygroscopic

catalog

▪ Nomenclature of chain monosaccharides
▪ Nomenclature of cyclic monosaccharides
five nature
▪ physical property
▪ chemical property

definition

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Monosaccharides just can't hydrolysis Sugar of Disaccharide And the basic unit of a polysaccharide molecule.^[2]

Encyclopedia x confusion: diagram of monosaccharide and polysaccharide

classification

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According to the number of carbon atoms, monosaccharides can be divided into Triose , butyl sugar Pentose , hexose, etc. The monosaccharides in nature are mainly pentose and Hexose 。 According to structure, monosaccharides can be divided into aldose and Ketose 。 Polyhydroxy aldehyde is called aldose hydroxyl Ketone is called ketose. For example, glucose is Hexaldose ， fructose It is hexulose. Among monosaccharides, glucose is the most important and closely related to people. The common monosaccharides are fructose Galactose 、 Ribose and Deoxyribose etc.^[3] 。

structure

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cyclic structure	In solution, monosaccharides containing more than 4 carbon atoms mainly exist in a ring structure. The hydroxy group in the monosaccharide molecule can be inversely condensed with the aldehyde or ketone group to form a cyclic semi acetal (emiacetal). Cyclization Then, the carbonyl C becomes a chiral C atom, which is called end isomerism carbon atom (anomic carbon atom), two types formed after cyclization Diastereomer be called Terminal base Isomers, or head isomers, are called α- Type and β- Head isomers. The ring structure is generally represented by the Haworth structural formula. It is not convenient to use Fischer projection to express the ring structure. Haworth structural formula is more accurate than Fischer projection formula in reflecting the Bond angle And key length. Conversion method: ① Draw a five or six yuan ring ② Start from the anomerio carbon on the right side of the oxygen atom and draw Semiacetal hydroxyl In Fischer projection formula, the right side is below the ring and the left side is above the ring. The molecular formula of glucose is C six H twelve O six The molecule contains five hydroxyl groups and one aldehyde group, which is hexaldose. C-2, C-3, C-4 and C-5 are different Chiral carbon Atoms, 16（ α 4=16) with optical rotation Isomers of, D-glucose Is one of them. Glucose in nature Fischer Projection, four Chiral carbon atom Except the - OH on C-3 is on the left, the - OH on other chiral carbon atoms is on the right. D/L method is still used to determine monosaccharide configuration. This method only considers carbonyl The configuration of a chiral carbon farthest from each other. The hydroxyl group on the chiral carbon is D-type on the right and L-type on the left. Most monosaccharides in nature belong to D-type sugar.
The ring structure of glucose and its spin change	There are two kinds of crystalline glucose, one is crystallized from ethanol, melting point 146 ℃. Its new solution[ α] D is+112 °, and the specific rotation of this solution gradually decreases during storage, and remains unchanged after reaching+52.17 °; The other is from pyridine With melting point of 150 ℃ and newly prepared solution[ α] D is+18.7 °, and the specific rotation of this solution is gradually It also rises and remains unchanged after reaching+52.7 °. The phenomenon that the specific rotation of sugar in solution automatically changes to a fixed value is called the phenomenon of rotation change. Obviously, the open chain structure of glucose can not explain this phenomenon. It can be seen from the open chain structure of glucose that it has both aldehyde groups and alcohol hydroxyl groups, so it can form cyclic semi acetals within the molecule. During cyclization, the carbonyl group of glucose reacts with the hydroxyl group on C-5 to form a stable six membered ring. Although glucose molecule has Aldehyde group However, there are many differences with general aldehydes in reaction performance. For example, the addition of NaHSO3 is very slow, because glucose almost exists in the form of cyclic semi acetal structure in solution. After cyclization, the original carbonyl carbon atom (C-1) becomes chiral carbon atom There are two possible spatial arrangements of the newly formed semi acetal hydroxyl groups on C-1. Semi acetal hydroxyl and hydroxyl (hydroxyl on C-5) determining monosaccharide configuration Carbon chain The same side is called α Type, on the opposite side is called β Type. α Type and β Type yes no Enantiomer 。 Their difference is the configuration on C-1, so they are also called Heterocephaly (terminal isomers). Their melting point and specific optical rotation are different. Grape The phenomenon of sugar spin change is caused by the change of specific rotation in the process of forming an equilibrium system between the open chain structure and the ring structure. In solution α- D-glucose can be transformed into open chain structure, and then from open chain structure to β- D-glucose ； same β- D-glucose is also transformed into an open chain structure, and then into α- D-glucose. After a period of time, the three isomers reach equilibrium, forming a Tautomerism In the equilibrium system, the specific optical rotation does not change. Not only do grapes have the phenomenon of rotation change, but all monosaccharides that can form a circular structure will have the phenomenon of rotation change.^[4]
Haworthian and Conformational Forms of Ring Structure	The above vertical ring Fischer projection Although it can represent the cyclic structure of monosaccharides, it can not accurately reflect the spatial arrangement of atoms or atomic groups in monosaccharides. For this reason, Haworth proposed to use perspective expression. Haworth rewrote the vertical ring form into the flat ring form. Because the ring structure of glucose is composed of five carbon atoms and one Oxygen atom A heterocycle composed of Heterocyclic compound In Pyran Similar, so it is called Pyranose 。 The atoms or atomic clusters connected to the ring are written on the top and bottom of the ring respectively to indicate the arrangement of their positions. In writing Hastwald's form, carbon atoms are often omitted as rings, and the three C-C bonds facing the front are represented by thick solid lines. For D-glucose, the hydroxyl group on the right side of the vertical ring type is below the ring plane in the Hass type; The left hydroxyl in the vertical ring form is above the ring plane. During cyclization, in order to make the hydroxyl group on C-5 Aldehyde group Approach. The C (4) - C (5) single bond must be rotated by 120 °. Therefore, the hydroxymethyl group at the end of D-type sugar is above the ring plane. Newly formed on C-1 Semiacetal The hydroxyl group below the ring plane is α Type; Those above the ring plane are called β Type. In fact, the atoms forming the pyran ring are not completely in one plane, but exist in a more stable chair conformation. Therefore, in order to reflect its structure more reasonably, it is often expressed by conformational formula. α- D-glucopyranosyl, except for the connection of - OH on C-1 α - OH and - CH on the other three carbons two OH is connected to the e bond, and β- D - OH on glucopyranosyl C-1 and all relatively large atomic groups (- OH, - CH two OH) are connected to the e bond, so β The conformation of type A is more stable. So when equilibrium is reached in the solution, β Type accounted for 64%, while α Type A only accounted for 36%.

name

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"Monosaccharide" refers to a single (sugar) unit that does not exist with other similar units Glycosidic bond Connected compounds. From the functional group analysis, the monosaccharide parent is a polyhydroxyaldehyde H - [CHOH] containing three or more carbon atoms n - CHO or polyhydroxy ketone H - [CHOH] n —CO—[CHOH] m - H, some sugars have amino groups. It includes aldose , dialdehyde sugar, aldehyde ketose Ketose , diketose, deoxysaccharide, amino sugar and their derivatives.^[8]

Common names are often used for monosaccharides. The configuration of monosaccharides is marked by the configuration of the chiral center with the highest position, and its configuration is divided into D or L configuration by the relative configuration representation; Racemate Represented by the prefix DL -, Racemate Use prefix“ meso ”To represent; The optical activity of sugar can be marked with (+) -, (−) - or (±) - before the configuration prefix; The end group configuration of the cyclic structure of sugar α or β Marking, α The isomer refers to that the oxygen atom outside the ring on the end group center and the oxygen atom on the configuration label atom are cis in the Fischer projection formula（ cis ）Isomers of; β The isomer is trans（ trans ）Isomers of; Terminal isomer symbol α or β Write before the sugar configuration symbol D or L, and connect them with a short line. Oligosaccharides, polysaccharides and sugar derivatives are named by common names of monosaccharides plus semi systematic names.^[8]

Nomenclature of chain monosaccharides

Nomenclature of monosaccharides	Monosaccharides are named according to the name of the open chain structure of the parent monosaccharide. Monosaccharide parent can be named systematically, according to the number of carbon atoms of sugar, it can be named as three carbon sugar (triose), four carbon sugar (butanose), five carbon sugar (pentose), six carbon sugar (hexose), etc; The configuration of sugar is indicated by the prefix of common name, such as D-glucose hexose. Compared with the systematic naming of sugar, common names of sugar are more commonly used, and most of C3~C6 sugars have common names.^[8]	The structure, system name and common name of the D-configuration parent aldose and ketose with 3-6 carbon atoms (3 sheets)
Nomenclature of high carbon sugar	For aldoses and ketoses containing more than four chiral centers, two or more configuration prefixes should be added before the main words when naming them. The first part written should be the part furthest from C-1 (maybe less than 4 atoms). The configuration of sugar depends on the configuration of the chiral carbon with the highest number.^[8]	Nomenclature of high carbon sugar (3 sheets)

Nomenclature of cyclic monosaccharides

Most monosaccharides exist in the form of five membered ring, six membered ring semi acetals or semi ketals. The five membered cyclic semi acetal or semi ketose is called furanose, and the six membered cyclic semi acetal or semi ketose is called pyranose. When naming, add "furan" or "pyran" before the name of raw sugar (note: naming according to custom, this is different from the word formation in IUPAC's English naming), such as Furan glucose (glucofuranose) or glucopyranose. The novice center formed by the closed loop is called the end group center, and the two stereoisomers are called the end group isomers α or β Identification. α The isomer refers to that the oxygen atom outside the ring on the end group center and the oxygen atom on the configuration label atom are cis in the Fischer projection formula（ cis ）Isomers of, β The isomer is trans（ trans ）The isomer of, indicating the symbol of end group isomer“ α” Or“ β” Write the connection number before the symbol "D" or "L" indicating the configuration.^[8]

Fischer Projection Representation of Ring Structure	If you want to use Fischer projection formula to express a ring sugar, you can use a long bond to connect specific alcohol hydroxyl groups and terminal carbon.
Haworth Representation of Ring Structure	Write the sugar pyranoside in the shape of a six membered ring, which is nearly perpendicular to the paper surface. When observing from the top to the bottom, the oxygen on the ring is at the rear and C-1 is at the right. Therefore, the side close to the observer should be at the bottom of the far side. In order to mark the perspective situation more clearly, the keys on the side close to the observer are usually bold. The right facing group in Fischer projection formula is below the ring plane in Haworth perspective formula; The left is above the ring plane. The Haworth formula of some other sugars can be expressed similarly. The six membered ring of Haworth type is not a plane, but exists in a chair conformation like cyclohexane. In order to clearly mark the conformation of pyranose, the Haworth type is written as a chair type conformation, and the hydrogen atom on the carbon is often omitted.
Mills Representation of Ring Structure	The circular structure of monosaccharides can also be written in Mills, especially when additional ring structures appear, the structural formula of Mills is clearer. Mills type representation is to draw the main semi acetal ring on the paper plane, the substituent connected by the dotted line bond refers to the group in the paper plane, and the group connected by the thickened bond refers to the group outside the paper plane.^[8]

Fischer Projection Representation of Ring Structure

Haworth Representation of Ring Structure

Haworth representation of ring structure (chair conformation)

Mills Representation of Ring Structure

nature

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physical property

Monosaccharides are usually colorless crystals that are easily soluble in water, and most of them are hygroscopic. Insoluble in ethanol, insoluble in Ether 。 Monosaccharides are optically active, and solutions of monosaccharides with more than four carbons are Trochanter phenomenon 。

chemical property

Monosaccharides with more than four carbons mainly exist in the form of ring structure, but can react in the form of open chain structure in solution. Therefore, some chemical reactions of monosaccharides are carried out in a ring structure, and some are carried out in an open chain structure.

Epimerism	When glucose is treated with dilute lye, it will partially change into mannose And fructose, becoming a complex mixture. This change is accomplished through the enol type intermediate. D-fructose 、 D-mannose and D-glucose The structures of C-3. C-4, C-5 and C-6 are identical, only the structures of C-1 and C-2 are different, but their structures are identical when the structures of C-1 and C-2 become enol type. Therefore, not only D-glucose, but also D-fructose or D-mannose can be transformed into a mixture of the three under the catalysis of dilute alkali. Among optically active isomers containing multiple chiral carbon atoms, when the configuration of only one chiral carbon atom is different, they are called epimers. D-glucose and D-mannose are C-2 Epimer 。 Therefore, the reaction of treating D-glucose with dilute alkali to obtain a balanced mixture of D-glucose and D-fructose is called Epimerization 。
oxidation	Monosaccharides, whether aldose or ketose, can be mixed with weak oxidant Yellen reagent Fehling's solution and Benedet reagent Function to generate metal or low valence oxide of metal. The above three reagents are alkaline weak oxidants. Monosaccharides are heated in alkaline solution to form complex mixtures. Monosaccharides are easily oxidized by alkaline weak oxidants, indicating that they are reducible, so they are called reducing sugar 。 When monosaccharides are oxidized under acidic conditions, the oxidation products of monosaccharides are different due to the different strength of oxidants. For example, glucose is brominated During oxidation Gluconic acid ； And use Strong oxidant When nitric acid is oxidized, glucose diacid is formed. Bromine water has weak oxidation ability, and it converts aldose Aldehyde group Oxidation to carboxyl group. When bromine water is added to aldose and heated slightly, the brown color of bromine water will fade, while ketose will not be oxidized, so bromine water can be used to distinguish aldose from ketose Ketose 。
Glycosidation	When the semiacetal hydroxyl group in the cyclic semiacetal structure of monosaccharide interacts with another alcohol or hydroxyl group, one molecule of water is removed to form acetal. This acetal of sugar is called Glycoside 。 for example α- and β- A mixture of D-glucopyranose at Hydrogen chloride Under catalysis, it reacts with methanol to remove a molecule of water and generate α- and β- D-methylpyran Glucoside A mixture of. α- and β- D-pyran grape mixture β- D-methylglucopyranoside α- D-methylglucopyranoside, which is composed of sugar and non sugar parts. The non sugar part is called Glycoside ligand or Aglycone 。 Sugar and glycoside ligands are connected through "oxygen bridge" after dehydration, and this bond is called Glycosidic bond 。 Because the cyclic structure of monosaccharide has α- and β- Two configurations, so it can generate α- and β- Two glycosides without configuration. Natural glycosides are mostly β- Configuration. Glycosides are named according to their components, and glycoside bonds and sugar configurations are pointed out. Natural glycosides are commonly known according to their origin. There is no semi acetal hydroxyl group in the glycoside structure, and it can no longer be converted into an open chain aldehyde structure in the solution, so the glycoside has no reducibility and no spin change. Glycosides are relatively stable in neutral or alkaline environments, but in acidic solutions or under the action of enzymes, they hydrolyze to form sugar and non sugar parts. Glycoside is one of the effective ingredients of Chinese herbal medicine, which is mostly colorless, odorless, and bitter solid, but flavonoid glycosides and anthraquinone glycosides are yellow. Glycosides contain sugar, so they are soluble in water. Glycosides are optically active, and most natural glycosides are Levorotator 。
Esterification	Monosaccharides contain multiple hydroxyl groups, which can react with acids to form esters. Glucose in human body generates glucose phosphate under the action of enzyme, such as 1-glucopyranosyl phosphate and 6-glucopyranosyl phosphate. Monosaccharide phosphate They are important in the process of life. They are the intermediate products of many metabolism in the human body.
Osazone reaction	Monosaccharide molecules interact with three molecules of phenylhydrazine to produce a product called osazone. For example, glucose reacts with excessive phenylhydrazine to produce glucose Osazone. Both aldose and ketose can form osazone, and osazone formation reaction can be regarded as α- Hydroxy aldehyde or α- Specific reactions of hydroxy ketones. Osazone is a yellow crystal that is insoluble in water. Different osazone have characteristic crystal shape and certain melting point. Osazone and these properties are often used to identify different sugars. Osazone reaction only occurs on C-1 and C-2 of monosaccharide molecules, and does not involve others carbon atom Therefore, except for C-1 and C-2, sugars with the same carbon atom configuration can all generate the same osazone. For example, D-glucose and D-fructose both produce the same osazone.
Reduction reaction	Monosaccharides can be reduced to corresponding sugar alcohols. D-glucose is reduced to D-glucose alcohol, also known as D-Sorbitol. Sugar alcohol is mainly used in food processing industry and medicine, and sorbitol is added to candy It can extend the shelf life of candy, because it can prevent the candy from losing water. The juice treated with saccharin usually has aftertaste d-Sorbitol It can remove the aftertaste. After human consumption, melitol will be converted into fructose in the liver^[5] 。

Monosaccharide classification

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The monosaccharides discovered in nature are mainly pentose and hexose. The common pentoses are D - (-)- Ribose 、D-（-）-2- Deoxyribose 、D-（+）- xylose And L - (+)- Arabinose 。 They are aldoses, which exist in animals and plants in the form of polysaccharides or glycosides. Common hexoses are D - (+) - glucose, D - (+) - mannose, D - (+)- Galactose D - (-) - fructose, the latter is ketose. Hexose exists in animals and plants in free or combined form.

Name of monosaccharide	introduce
Ribose	Ribose, which exists in yeast and cells in the form of glycoside, is an integral part of nucleic acid, some enzymes and vitamins. In addition to ribose, there is also 2-deoxyribose (called deoxyribose for short) in nucleic acid. The ring of ribose and deoxyribose is furan ring, so it is called furanose. β- D - (-) - furan ribose β- D - (-) - deoxyfuran Ribonucleic acid Ribose in or deoxyribose on C-1 β- Glycoside bond to ribonucleoside or Deoxyribonucleoside , collectively referred to as nucleosides. The ribose or deoxyribose in the nucleoside is combined with phosphoric acid by ester bond with the hydroxyl group on C-5 or C-3 nucleotide 。 Nucleotides containing ribose are collectively referred to as Ribonucleotide , the basic unit of RNA; Nucleotides containing deoxyribose are collectively referred to as Deoxyribonucleotide Is the basic unit of DNA.
glucose	D - (+) - glucose is widely distributed in nature, especially in grapes, so it is called glucose. Glucose also exists in human blood (389-555umol/l) blood sugar 。 The urine of diabetic patients contains glucose, and the sugar content varies with the severity of the disease. Glucose is a variety of sugars, such as sucrose malt dust 、 lactose , starch Glycogen , cellulose, etc. Glucose is a colorless crystal or white crystalline powder, melting point 146 ℃, easily soluble in water, and difficult to dissolve in alcohol , sweet. Natural glucose is dextral, so it is also called Dextrose 。 In the liver, glucose is oxidized into grapes by enzymes Uronic acid That is, the hydroxymethyl group on the end of glucose is oxidized to carboxyl group. Glucuronic acid In the liver, it can combine with toxic substances such as alcohol and phenol to form non-toxic compounds, which can be discharged from the body by urine Detoxification 。
Galactose	Galactose combines with glucose to form lactose, which is found in mammal Galactose is also found in some cerebrosides with complex structure in the brain marrow. Galactose is hexaldose, the diastereomer of glucose. The only difference between the two is that the configuration of C-4 is just opposite, so they are the epimers of C-4. Galactose also has a ring structure, also on C-1 α- and β- Two configurations. α- D-galactopyranose β- D-galactopyranose Galactose is a colorless crystal with a melting point of 165-166 ℃. half lactose yes Reducibility There is also the phenomenon of rotation change, and the specific rotation at equilibrium is+83.3 °. Galactose in human body is the hydrolysate of lactose in food. Galactose can be converted into glucose under the catalysis of enzyme. Some derivatives of galactose are widely distributed in the plant kingdom. For example, Galacturonic acid It is the main component of plant mucus; Carrageenin 9 is also called agar ）The main composition of is the high polymer of galactose derivatives.
fructose	D-fructose, a constituent unit of sucrose, exists in fruits and honey in a free state semen It also contains a considerable amount of fructose. Fructose is colorless crystal, easy to use and soluble in water, and its melting point is 105 ℃. D-fructose is Levulose There is also the phenomenon of rotation change, and the specific rotation at equilibrium is - 92 °. This equilibrium system is a mixture of open chain and ring fructose. β- D - (-) - Fructopyranose β- D - (-) - furan fructose When fructose is free, it mainly exists in the form of pyran ring; when it is bound, it mostly exists in the form of furan ring. Fructose can also form phosphate esters. Fructose-6-phosphate ester (represented by F-6 -) and fructose-1,6-diphosphate (represented by F-1,6-di) are present in the body. Fructose phosphate in vivo Carbohydrate metabolism It plays an important role in sugar metabolism. F-1,6-di can be produced under the catalysis of enzyme Glyceraldehyde -3-phosphate and dihydroxy acetone Phosphate ester. The body changes hexose into triose through this reaction, which is an intermediate step in the process of sugar metabolism. This reaction is similar to Aldol condensation reaction The reverse reaction of.
Aminosugar	Amino sugar in nature is a derivative of hexaldose in which the hydroxyl group on C-2 is replaced by amino group. β- D- aminoglucose β- D-galactosamine Amino sugars are often present in mucin and glycoprotein However, free galactosamine is toxic to the liver.
Uronic acid	The hydroxyl group furthest from the aldehyde group in the aldose is oxidized to carboxyl It is made of sugar and acid. Natural uronic acids include D-glucose, D-mannose and D-galactose The three derived hexuronic acids are animal, plant and Microbial polysaccharide Of which only Galacturonic acid It can exist in plant fruits in free state. In animals, D- Glucuronic acid It has the function of detoxification. There are many kinds of glycosides that can combine with D-glucuronic acid, generally small molecule compounds, including phenols, aromatic acids, fatty acids Aromatic hydrocarbon Etc. Generally, the ratio of glycosyl group to D-glucuronic acid is 1 ∶ 1, with few exceptions. The binding site is mainly in the liver.
Deoxysaccharide	Monosaccharide hydroxyl A compound formed by the substitution of hydrogen. As D-2- Deoxyribose Is a component of DNA; L-fucose is a component of some glycoproteins, which is L-6-deoxygalactose.
Nucleoside diphosphate sugar	Nucleoside diphosphate sugar monosaccharide and nucleoside diphosphate terminal phosphate group are connected by glycosidic bond. The activated glycosyl group is involved in many metabolic reactions, especially oligosaccharide And polysaccharide biosynthesis 。 More than 100 kinds of natural nucleoside diphosphate sugars have been studied, such as UDP glucose, ADP glucose, CDP glucose, GDP glucose and TDP glucose. Uridine diphosphate glucose (uridine diphosphate glucose, UDPG) can be used as the representative of nucleoside diphosphate sugar.

absorb

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Sugar has been digested into monosaccharides in the small intestine, so it can be digested into monosaccharides in the small intestine epithelial cells Absorb into the blood. According to absorbed rate Monosaccharides can be divided into two categories: galactose and glucose belong to the category of fast absorption; Fructose is a kind of slow absorption.

The absorption of glucose (or galactose) is related to Na + Coupled, they use a carrier protein located on the striated edge of intestinal mucosa epithelium together. Because Na in intestinal cavity + The concentration of Na is higher than that of Na in cells + Accessible Carrier protein Combine with the concentration difference and enter the cell, as long as the intestinal cavity maintains a high concentration of Na + , can take the glucose to transport into the cells actively until the glucose in the intestinal cavity is completely transported. When Na + And glucose enter the cell, and then they are separated from the carrier. Na + It can be actively transported to the intercellular space by the sodium pump on the cell side membrane. Glucose molecules diffuse through the lateral membrane and Basement membrane Cell outgrowth. The fructose in the intestinal cavity may be Facilitation Diffuse transport into villous epithelium^[3] 。

scientific research

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In November 2022, Chinese scientists will study It was found that monosaccharide and disaccharide (sweet taste) were positively selected during watermelon domestication.^[7]

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