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Glucose is more stable than galactose and is less susceptible to the formation of nonspecific glycoconjugates, molecules with at least one sugar attached to a protein or lipid. Many speculate that it is for this reason that a pathway for rapid conversion from galactose to glucose has been highly conserved among many species.
To name conformations of pyranose, first the conformer is determined. The common conformers are similar to those found in cyclohexane, and these form the basis of the name. Common conformations are chair (C), boat (B), skew (S), half-chair (H) or envelope (E). The ring atoms are then numbered; the anomeric, or hemiacetal, carbon is always 1 ...
A open-chain form of glucose makes up less than 0.02% of the glucose molecules in an aqueous solution at equilibrium. [57] The rest is one of two cyclic hemiacetal forms. In its open-chain form, the glucose molecule has an open (as opposed to cyclic) unbranched backbone of six carbon atoms, where C-1 is part of an aldehyde group H(C=O)−.
O-GlcNAc differs from other forms of protein glycosylation: (i) O-GlcNAc is not elongated or modified to form more complex glycan structures, (ii) O-GlcNAc is almost exclusively found on nuclear and cytoplasmic proteins rather than membrane proteins and secretory proteins, and (iii) O-GlcNAc is a highly dynamic modification that turns over more ...
The chair conformation of six-membered rings have a dihedral angle of 60° between adjacent substituents thus usually making it the most stable conformer. Since there are two possible chair conformation steric and stereoelectronic effects such as the anomeric effect, 1,3-diaxial interactions, dipoles and intramolecular hydrogen bonding must be taken into consideration when looking at relative ...
For example, the aldohexose glucose may form a hemiacetal linkage between the aldehyde group on carbon 1 and the hydroxyl on carbon 4, yielding a molecule with a 5-membered ring, called glucofuranose. The same reaction can take place between carbons 1 and 5 to form a molecule with a 6-membered ring, called glucopyranose.
The two have equal free energy; neither is more stable, so neither predominates compared to the other. A negative difference in free energy means that a conformer interconverts to a thermodynamically more stable conformation, thus the equilibrium constant will always be greater than 1.
However, in order for anomers to exist, the sugar must be in its cyclic form, since in open-chain form, the anomeric carbon atom is planar and thus achiral. More formally stated, then, an anomer is an epimer at the hemiacetal/hemiketal carbon atom in a cyclic saccharide. [1] Anomerization is the process of conversion of one anomer to the other.