Glucid

glucids or carbohydrates are a class of of . Their chemical formula is based on the model CN(H2O)p.

They form part, with and them , of the essential components of the alive beings and of their , because they are one of the principal biological intermediaries of storage and consumption of. At the organizations , like , them is converted into for storage. At the organizations , like , they are used as source of energy in the metabolic reactions.

Synopsis

Categories

glucids (improperly named carbohydrates) are usually distributed enters (monosaccharides and disaccharides) with the sweetened taste and , insipid, like.

  • (or monosaccharides) is simple molecules, not hydrolysables, forming crystals, commonly called sugars
  • glycosides, hydrolysables is polymers of oses bound by one osidic connection :
    • holosides are exclusively of oses;
      • oligoholosides (oligosides) have an index of polymerization lower than 10;
      • polyholosides (polyosides) have an index of polymerization higher than 10 (example: , amylopectin, , ).
    • heterosides are of oses and nonglucidic molecule itaglycone :

Structure, classification and nomenclature

Simple oses

The oses have a whole a function carbonyl :

  • for aldoses (example: );
  • for the ketoses (example: ).

They are characterized by their number of :

Linear representation: model of Fischer

All the oses have one optical activity because of the presence of one asymmetrical carbon, the oses are known as chiral.

Figure 1 : représentation de Fischer des formes D et L du glucose. Les deux sont symétriques par rapport à un plan.
Figure 1: representation of Fischer of the forms D and L of glucose. Both are symmetrical compared to a plan.

Two (antipodes optical) has same the properties except for only one: their optical activity opposed. Figure 1 accounts for both of , the form D-glucose is the natural form.

  • In the form D, the grouping alcohol (- OH) carried by carbon <maths>n-1</maths> is with right-hand side (of representation of Fischer);
  • In the form L, the grouping alcohol (- OH) carried by carbon <maths>n-1</maths> is with left (of representation of Fischer).

Cyclic representation: model of Haworth

When one leaves a solution in the water of glucose beforehand cristalized in water, the capacity passes from +112° to +52,5°. When one leaves a solution in the water of glucose beforehand cristalized in acid ethanoïc, the capacity passes from +19° to +52,5°.

Figure 2 : cyclisation du D-glucose. Les formes cycliques sont des hémiacétals
Figure 2: cyclization of D-glucose. The cyclic forms are hémi

This observation is due to the fact that the function of glucose is hydrated to form a function which will react with the another function alcohol (that of carbon 5). Glucose becomes cyclic then, it derives from pyrane. Carbon n°1 is a carbon anomère, the grouping of the function alcohol which it door can be "in top" or "bottom". If it is in top, carbon is in form beta, if not, it is the form alpha. Figure 2 explains the cyclization of glucose. In aqueous solution, it is in tautomeric balance: 65 % in form?-D-glucopyrannone, 0,1% pennies form D-glucose (linear) and 35 % of?-D-glucopyrannose.

Figure 3 : formes α et β du fructofurannose.
Figure 3: forms? and? fructofurannose.

, cétohexose, cyclise by reaction is entered carbons 1 and 4, this form derives from furane, it is the furannic form (figure 3). Glucose also but D-glucofurannose is not stable and is transformed quickly into D-glucopyrannose.

cyclisant itself in furan form is:

  • giving ribofurannose;
  • 2 giving 2-désoxyribofurnannose;
  • giving fructofurannose.

cyclisant itself in pyranic form is:

  • giving glucopyrannose;
  • giving galactopyrannose.

Glycosides

Glycosides are of bound by a osidic connection.

Formation of the osidic lisaison

One osidic connection is one produces reaction between the hemiacetalic function alcohol (- OH formed by carbon anomère) and another molecule (glucidic or not).

To consult the article about osidic connection for more information.

Holosides

It is a diholoside not reducer, its name official is the <maths>\alpha - D-glucopyrannosyl(1\rightarrow 2)\beta - D-fructofurannoside</maths>

It is a reducing diholoside, it is the glucid of , its name official is the <maths>\beta - D-galactopyrannosyl(1\rightarrow 4)-D-glucopyrannose</maths>

It is a diholoside homogeneous reducer, its name official is the <maths>\alpha - D-glucopyrannosyl(1\rightarrow 4)D-glucopyrannose</maths>

cellobiose

It is a diholoside homogeneous reducer, its name official is the <maths>\beta - D-glucopyrannosyl(1\rightarrow 4)D-glucopyrannose</maths>

raffinose

It is a triholoside not reducer, its name official is the <maths>\alpha - D-galactopyrannosyl(1\rightarrow 6)\alpha - D-glucopyrannosyl(1\rightarrow 2)\beta - D-fructofurannoside</maths>.

Determination of the structure of a diholoside

(to be supplemented)

Polyholosides

It is a homogeneous polyholoside not reducer made up of two made up:

  • The amylose, polymer of glucose bound by a connection?(1 -- >4);
  • The amylopectin, amylose ramified by a connection?(1 -- >6).

The starch is a polymer of . It is the glucidic substance of reserve of plants. The starchy foods are a major source of starch in the human consumption.

It is structurally identical to. But its is higher (about <maths>10^{6} G.mol^{-1}</maths>). It is the glucidic substance of reserve of the animals.

at summer extracted by in 1856 in the liver. It is the shape of storage of surplus glucose at the animals and mushrooms. It also acts of a polymer of ramified glucose (a connection every 6 to 8 units glucose). The glycogen is formed by and broken up by glycogénolyse.

It is a homogeneous polyholoside of glucose bound by a laison?(1 -- >4).

The principal molecule structural of the plants is . Wood is partly composed of cellulose, while paper and cotton are almost pure cellulose. The cellulose is a polymer of glucose. It is a very long and rigid molècule, of which the structure confers its mechanical properties to him as observed at the plants.

It is a mixed polyholoside made up of D and L-galactose esterified by. Extracted from algae, it is used in bacteriology and in food industry like gelling.

acid hyaluronic

It is a mucopolysaccharide consists ofacid-?-glucuronique and of N-acétylglucosamine connected by a connection?(1 -- >3). It is one of the principal components of fundamental substance .

They consist of one base nitrogenized, of one (, 2)) and of a grouping . It is N-heterosides

Let us quote it, and its derivatives used in the transport of intracellular energy, the ribonucleic acid (ARN) charged to guide the cellular synthesis of , desoxyribonucleic acid (ADN) carrying heredity...

ONPG

Used in systematic bacteriology, itorthonitrophényl-?-D-galactopyrannoside is hydrolized by a?-galactosidase.

It is one O-heteroside.

Chemical properties

Reducing properties

Simple oses and diholosides having free their carbon hemiacetalic free are reducing from their function . The function is oxidized in function . One of the functions primary can be oxidized in function .

The diholosides not reducers are those of which no carbon hemiacetalic is not free, it is brought into play in osidic connection.

  • Reduction of the ions metalic

Reduction of the ion II (Cu2+) out of copper oxide II (Cu2O) (Fehling's solution). This property is used in method of Bertrand for the proportioning of glucids.

  • Reduction of organic compounds

For example 3,5-dinitrosalicylate (DNS) is tiny room in 3-amino-5-nitrosalicylate, made up brown red permentant to proportion the reducing oses by .

  • Oxidation by enzymatic way

In the presence of , glucose oxide it in gluconolactone (then acid gluconic) with release ofhydrogen peroxide. This is used to measure .

Hydrolize osidic connection

Chemical hydrolysis

The chemical hydrolysis is not specific, it leads to the smallest sub-unit of glucids : . It is réaliasée in the presence of

Enzymatic hydrolysis

The enzymatic hydrolysis, contrary to the chemical hydrolysis is specific. These is .

Metabolism of glucids

Degradation

glucids are or isomerized in (or ) then degraded in by , or, for bacteria, the way of. , is, according to the conditions, fermented out of lactate or ethanol. Into aerobiosis, it is transformed into acétylCoA and oxaloacétate. Lastly, the latter return in which releases from and of.

Synthesis

(to be supplemented)

Regulation

(to be supplemented)

See too

Internal bonds

External bonds

 

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