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Carbohydrates

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The phosphorylation of sugars is an indispensable step in the assembly of the building blocks of living matter. One of the carbon atoms is double bonded to an oxygen atom to form a carbonyl group;. In the figures given, not all of the hydrogen atoms attached to the ring carbons of cyclohexane are equivalent.

Table 1  Complexity Simple  Carbohydrates
Table 1 Complexity Simple Carbohydrates

Fructose or laevulose) is a simple reducing sugar (monosaccharide) (Fig. 3) found in many foods and is one of the three most important blood sugars along with glucose and galactose. As a component of the RNA used for genetic transcription, ribose is critical to living things. It is a deoxysugar derived from the pentose sugar ribose by replacing the hydroxyl group at the 2-position with hydrogen, resulting in the net loss of an oxygen atom.

The second carbon and a hydroxyl group are attached to one of the carbon atoms adjacent to the oxygen. In deoxyribose, the carbon farthest from the attached carbon is removed for the oxygen atom in what would be a. One of the common bases is adenine (a purine derivative); coupled to ribose it is called adenosine; linked to deoxyribose it is called deoxyadenosine.

In these structures, carbon 3 of one monomer unit is attached to a phosphate that is attached to carbon 5 of the other unit, and so on. One end of the backbone has a free 5'phosphate, and the other end has a free 3'OH group.

Disaccharide a. Sucrose

In plants, the presence of trehalose is seen in sunflower seeds, selaginella mosses and seaweed. The mushroom family is dominated by shiitake (Lentinula edodes), maitake (Grifola fondosa), nameko (Pholiota nameko) and Jew's ear (Auricularia auricula-judae) mushrooms, which contain 1% to 17% of trehalose in dry form. . Trehalose is metabolized by many bacteria, including Streptococcus mutans, the common oral bacteria responsible for dental plaque.

The enzyme trehalase, a glycoside hydrolase, breaks trehalose into two glucose molecules, which can then be easily absorbed in the intestine. Trehalose is the main carbohydrate energy storage molecule used by flying insects to be used as glucose for the rapid energy demand during flight. Thus, it is very difficult for them to digest milk and can contribute to gas, cramps and diarrhea.

The production of maltose from germinating grains, such as barley, is an important part of the brewing process. When barley is malted, it is brought to a state where the concentration of maltose-producing amylases has been maximized.

Trisaccharides a. Raffinose

The metabolism of maltose by yeast during fermentation then leads to the production of ethanol and carbon dioxide. Melesitose, also called melicitose, is a non-reducing trisaccharide sugar (Figure 22) produced from aphids such as Cinara pilicornis by an enzymatic reaction. This is beneficial to insects as it reduces osmotic stress by reducing their own water potential.

Melesitose is part of the honeydew produced by bees and acts as an attractant for ants. Since acarbose prevents the breakdown of complex carbohydrates into glucose, the carbohydrates will remain in the intestine. In the colon, bacteria will digest complex carbohydrates, causing gastrointestinal side effects such as bloating (78% of patients) and diarrhea (14% of patients).

Polysaccharides

Derivatives of Monosaccharide

Significant amounts of glucosamine have been found in the intestinal mucosa, which binds chloresterol and thereby limits its absorption. Glucosamine is an amino sugar derived from glucose, produced in the body from sugar glucose and the amino acid glutamine through the action of the enzyme glucosamine synthetase (Fig. 34). It therefore plays a role in the formation of cartilage and the cushioning synovial fluid between the joints; therefore it is.

Deficiencies or malfunctions in the ability to metabolize this sugar are linked to diseases of the bowel and bladder. Concentrated amounts of N-acetylglucosamine are found in the testes, liver, small intestine, epithelial cells of the endocrine and sebaceous glands and endothelial cells of blood vessels. N-. acetylgalactosamine is distributed to various other tissues, suggesting that it is important in the functional role of these tissues.

It is part of a biopolymer in the bacterial cell wall, built from alternating units of N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (MurNAc) linked by β(1→4) glycosidic bonds, cross-linked by oligopeptides at the lactic acid. acid residue of MurNAc. Peptidoglycan serves a structural role in the bacterial cell wall, providing structural strength, as well as counteracting the osmotic pressure in the cytoplasm.

Fig. 34: Glucosamine
Fig. 34: Glucosamine

Sugar phosphates

Derivatives of polysaccharides

Functions: The functions of chondroitin are largely dependent on the properties of the total proteoglycan of which it is a part. Structural: Chondroitin sulfate is an important component of the extracellular matrix and is important in maintaining the structural integrity of the tissue. In the nervous system, chondroitin sulfate proteoglycans regulate the growth and development of the nervous system, as well as the nervous system's response to injury.

Heparin is a member of the glycosaminoglycan family of carbohydrates (which includes the closely related molecule heparan sulfate). Heparin is a member of the glycosaminoglycan family of carbohydrates (which includes the closely related molecule heparan sulfate) and consists of a variably sulfated repeating disaccharide unit (Fig. 48). HS structure and differences from heparin: Heparan sulfate is a member of the glycosaminoglycan family of carbohydrates and is very closely related in structure to heparin.

The most common disaccharide unit within heparan sulfate is composed of a glucurone (GlcA) linked to N-acetylglucosamine (GlcNAc), typically making up about 50% of the total disaccharide units. For example, hyaluronan is an important component of synovial fluid and was shown to increase.

Fig. 47: Chondroitin sulfate
Fig. 47: Chondroitin sulfate

Sugars in the cell wall of bacteria

During birth, there is often a leak of the baby's red blood cells into the mother's circulation. The N-terminus of hydrophobic proteins attaches to the outer lipid membrane through a Ser (Fig. 55). The composition of the mold cell wall is characterized as a relatively simple structure consisting of "cellulose" and chitin.

The cell wall of the fungus can account for 30% or more of the dry weight of the fungus, and the fungi are characterized by external digestion of food followed by selective absorption of the digestive products. Where present, the α-glucan material appears as a fibrillar layer adjacent to the plasma membrane and is believed to play a largely structural role, stiffening the basal layer of the cell wall. The α-glucan layer is rarely shown in diagrams of the fungal cell wall because it does not appear in Saccharomyces, the usual model system.

This material may be peripheral to the bulk β(1→3)-glucan and is strongly involved in crosslinking the various cell wall components, as shown in the figure. The outer layer of the cell wall consists of various proteins with polysaccharide side chains consisting of mannose.

Fig. 53: Bacterial cell wall
Fig. 53: Bacterial cell wall

Derivatives with proteins

In N-glycosylation (Fig. 57), the addition of sugar chains to the amide nitrogen on the side chain of the asparagines can take place. For N-linked oligosaccharides, a 14-sugar precursor is first added to the asparagine in the polypeptide chain of the target protein. Proteoglycan-linking glycoproteins cross-link proteoglycan molecules and are involved in the formation of the ordered structure within cartilage tissue.

Actual binding of the sperm to the egg is mediated by glycoproteins that serve as receptors on the surface of each of the two membranes. The glycan moieties of the folding glycoprotein also lead to binding of the protein to lectins in the ER, which serve as molecular chaperones. On the other hand, the carbohydrate component of a glycoprotein is not a product of the ribosome.

For example, some bacteria use lectins to attach to the cells of the host organism during infection. The completed proteoglycan is then exported to the cell's extracellular matrix in secretory vesicles.

Fig. 57: Overview of the major types of vertebrate N-linked glycan glycosylation  There are two major types of N-linked saccharides: high-mannose oligosaccharides, in  essence, just two N-acetylglucosamines with many mannose residues, and complex  oligosac
Fig. 57: Overview of the major types of vertebrate N-linked glycan glycosylation There are two major types of N-linked saccharides: high-mannose oligosaccharides, in essence, just two N-acetylglucosamines with many mannose residues, and complex oligosac

Three-dimensional orientation

Synthesis: the protein component of proteoglycans is synthesized by ribosomes and transported into the lumen of the rough endoplasmic reticulum. In other words, two proteins would be identical glycoforms if they carried the same glycoprotein. It is very important to analyze the glycoform, since different glycoforms of the same glycoprotein have different biological properties.

Thus, i refers to a particular saccharide unit in the polymer chain, (i - 1) to the adjacent unit in the direction away from the non-reducing end, and (i + 1) in the direction of the non-reducing end. For these polysaccharides, the residue that forms this glycosidic bond is considered the first member of the chain. Because its position is important in unit specification, the torsion angle at the glycosidic bond is included in the sugar residue characteristics.

The torsion angle of the atoms A-B-C-D is the angle between A-B and C-D in a projection of the four atoms on a plane perpendicular to B-C. For the exact specification of the orientation of a polyatomic ring substituent, it is necessary to specify the torsion angle about the exo-cyclic bond.

Fig. 61: Atomic numbering
Fig. 61: Atomic numbering

Orientation of the glycosidic groups

Since this angle is related to the mode of attachment of the i-th residue, it can be designated ψ (i). However, it can be designated as ω (i ) since it refers to the adjacency of the ith residue. After mixing, tilt the tube and carefully add, without mixing, 0.5 mL of concentrated sulfuric acid down the side of the tube.

Prepare Bial's reagent by dissolving 0.3 g of reagent grade orcinol and 0.05 g of ferric chloride in 100 mL of concentrated (12 M) HCl. To test for pentoses, add 0.05 ml of 0.1% carbohydrate solution in water to 1 ml of Bial's reagent, and heat the solution in a boiling water bath for 2 minutes. To test for reducing sugars, add 0.2 ml of a 1% carbohydrate solution to 1 ml of Benedict's reagent and heat in a boiling water bath for 5 minutes.

Prepare Barfoed's reagent by dissolving 0.66 g copper acetate (monohydrate) and 0.18 mL glacial acetic acid in 10 mL distilled H2O. To test for reducing monosaccharides, add 0.3 mL of 1% carbohydrate solution to 0.6 mL of Barfoed's reagent and heat in a boiling water bath for 5 minutes,* then cool to room temperature.

Figure

Fig. 4: Epimers
Fig. 5: Disaccharide
Fig. 6:Cyclic form
Fig. 8: Enantiomers
+7

References

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