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Glycosidic bonds of the form discussed above are known as O-glycosidic bonds, in reference to the glycosidic oxygen that links the glycoside to the aglycone or reducing end sugar. In analogy, one also considers S-glycosidic bonds (which form thioglycosides ), where the oxygen of the glycosidic bond is replaced with a sulfur atom.
Glycolipid. Glycolipids are lipids with a carbohydrate attached by a glycosidic (covalent) bond. [1] Their role is to maintain the stability of the cell membrane and to facilitate cellular recognition, which is crucial to the immune response and in the connections that allow cells to connect to one another to form tissues. [2]
Much of the chemistry of glycosides is explained in the article on glycosidic bonds. For example, the glycone and aglycone portions can be chemically separated by hydrolysis in the presence of acid and can be hydrolyzed by alkali. There are also numerous enzymes that can form and break glycosidic bonds.
The glycosidic bond can be formed between any hydroxy group on the component monosaccharide. So, even if both component sugars are the same (e.g., glucose), different bond combinations (regiochemistry) and stereochemistry (alpha-or beta-) result in disaccharides that are diastereoisomers with different chemical and physical properties ...
One of the first and only examples of O-glycosylation on tyrosine, rather than on serine or threonine residues, is the addition of glucose to a tyrosine residue in glycogenin. [7] Glycogenin is a glycosyltransferase that initiates the conversion of glucose to glycogen, present in muscle and liver cells.
Amylopectin is synthesized by the linkage of α(1→4) Glycosidic bonds. The extensive branching of amylopectin (α(1→6) Glycosidic bond) is initiated by BE and this is what differentiates amylose from amylopectin. DBE is also needed during this synthesis process to regulate the distribution of these branches. [19] [22]
Cytosine, thymine, and uracil are pyrimidines, hence the glycosidic bonds form between their 1 nitrogen and the 1' -OH of the deoxyribose. For both the purine and pyrimidine bases, the phosphate group forms a bond with the deoxyribose sugar through an ester bond between one of its negatively charged oxygen groups and the 5' -OH of the sugar. [2]
This can result in different regioselectivity depending on the acceptor resulting in products with different glycosidic linkages. One example is the Agrobacterium sp. β-glucosynthase, which forms a β-1,4-glycoside with glucose as the acceptor, but forms a β-1,3-glycoside with xylose as the acceptor.