Alpha and Beta linkages in Polysaccharides - (Jul/08/2014 )
Hi, maybe a stupid question and I should already know this, but when linkages in polysaccharides are mentioned it has either alpha or beta mentioned before them. what does this refer to? e.g. α (1→4) linkages in glucans and β-1,4 linkage in chitin.
Thanks for any help
It refers to the position of the carbon from which the linkages are made.
Here's the appropriate quote from wikipedia http://en.wikipedia.org/wiki/Oligosaccharide_nomenclature:
Naming of oligosaccharides proceeds from left to right (from the non-reducing end to the reducing end) as glycosyl
n glycoses or glycosyl n glycosides, depending on whether or not the reducing end is a free hemiacetal group.%5B3%5D In parentheses, between the names of the monosaccharide residues, the number of the anomeric carbon atom, an arrow symbol, and the number of the carbon atom bearing the connecting oxygen of the next monosaccharide unit are listed.%5B3%5D Appropriate symbols are used to indicate the stereochemistry of the glycosidic bonds (α or β), the configuration of the monosaccharide residue (D orL), and the substitutions at oxygen atoms (O).%5B2%5DMaltose and a derivative of sucrose illustrate these concepts: