Hexose glucose

Hexoses glucose, fructose, mannose, sorbose, trehalose, galactose, JV-acetylglucosamine, j3-glucoside... 

Historically, techniques such as the formation of osazones and the demonstration of fermentation have contributed significantly to the separation and identification of carbohydrates. Observation of the characteristic crystalline structure and melting point of the osazone derivative, prepared by reaction of the monosaccharide with phenylhydrazine, was used in identification. This method is not completely specific, however, because the reaction involves both carbon atoms 1 and 2 with the result that the three hexoses, glucose, fructose and mannose (Figure 9.19), will yield identical osazones owing to their common enediol form. 

Specificity The transporter has a similar specificity to hexokinase it transports several hexoses, glucose, mannose, 2-deoxyglucose. Similarly, the optical isomer, D-glucose, but not L-glucose, is transported (Chapter 3). 

Six-carbon sugars (hexoses) and five-carbon sugars (pentoses) are the most frequently encountered monosaccharide carbohydrate units in nature. Primary examples of these two classes are the hexoses glucose and fructose, and the pentose ribose. Note the suffix -ose as a general indicator of carbohydrate nature. 

NADPH formed in the oxidative phase is used to reduce glutathione, GSSG (see Box 14-3) and to support reductive biosynthesis. The other product of the oxidative phase is ribose 5-phosphate, which serves as precursor for nucleotides, coenzymes, and nucleic acids. In cells that are not using ribose 5-phosphate for biosynthesis, the nonoxidative phase recycles six molecules of the pentose into five molecules of the hexose glucose 6-phosphate, allowing continued production of NADPH and converting glucose 6-phosphate (in six cycles) to C02. 

Monosaccharides carbohydrates that cannot be hydrolyzed (split, with the addition of HjO) into simpler carbohydrates. Typically, they contain 3,4,5, or 6 carbons (trioses, tetroses, pentoses, hexoses). Glucose (fig. 3.1) as well as fructose and galactose are examples of hexoses. 

Alcoholic Fennentation.—The statements, just made, in regard to the alcoholic fermentation of the di-saccharoses, need to be explained. Yeast, i.e., ordinary beer yeast, contains several enzymes. The definite enzyme present in yeast, and which, alone, produces alcoholic fermentation of sugars, is the enzyme Z3rmase. This enzyme acts only upon the hexoses glucose, fructose, and galactose. It has no action upon either of the three di-saccharoses we have mentioned. When, however, cane sugar or malt sugar is treated with ordinary yeast alcoholic fermentation takes place. This is due to a preliminary action of other enzymes upon the di-saccharoses by means of which they are converted into mono-saccharoses and then the mono-saccharoses are fermented... 

Figure 11 GC/MS assay of alditol hexa-acetates quantified against inositol internal standard (IS), (a) In the chromatogram shown here the monosaccharides making up a plant cell wall are being quantified as their alditol acetates, using inositol (Ino) as the (IS). The GC separation of these reduced sugars is essential for their identification. The mass spectra of the alditol acetates of the hexoses, glucose (Glc) (b), galactose (Gal) (c), and mannose (Man), are essentially identical, as are the mass spectra of the alditol acetates of the pentoses, xylose (Xyl) and arabinose (Ara), and the deoxysugars, rhamnose (Rhm) and fucose (Fuc).

Fig. 2.3. Glycolytic oscillations in a yeast extract subjected to constant injection of substrate. Chemical analysis shows that hexoses (glucose 6-phosphate, fructose 6-phosphate, fructose 1,6-bisphosphate) oscillate with the same frequency as NADH, whose fluorescence allows the continuous recording of the phenomenon (Hess et ai, 1969). 

The most important monosaccharide is glucose. Glucose is a hexose because it contains six carbon atoms. Like all hexoses, glucose has the formula C6H12O6. 

Ribose and deoxyribose are important as components of nncleic acids. The hexoses glucose, galactose, and fructose are the most important nutritionally and the most abundant in nature. Glucose, also known as blood sugar, is transported within the bloodstream to body tissues, where it supplies energy. 

The hexoses glucose and galactose differ in the positions of H and OH on carbon number 4. 

The number of bacterial strains that use peutoses beside hexoses is rather limited therefore, a multistep hydrolysis might be needed, followed by separation of the different sugars. In the case of lignoceUulose hydrolysate, pentoses are mainly represented by arabinose and xylose deriving from the hemicellulose fraction, whereas the hexose glucose is generated from the cellulose fraction. 

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