What is the difference between a glycosidic bond and peptide bond because both of them involve the elimination of water but what exactly is different in between them?
The bond connecting the anomeric carbon to the acetal oxygen is termed a glycosidic bond.
In general speaking, with respect to sugars, a bond between the anomeric carbon atom and the oxygen atom of the alcohol is called a glycosidic bond (this arrangement is termed an O-glycosidic bond).
Unlike peptide bond, the glycosidic bond can have several variations that it can be formed by through association of the anomeric carbon to other heteroatoms such as nitrogen as in nucleosides (anomeric carbon atom of a sugar linked to the nitrogen atom of an amine) and is specifically called an N-glycosidic bond.
e.g the glycosidic linkage is from the C-1’ carbon of the sugar to the N-1 nitrogen of pyrimidines or to the N-9 nitrogen of purines. Its not necessarily the bond between monosaccharides only
Another unique aspect of this bond is can exist in several structural forms depending on how anomeric form of the sugar is involved in the bond, and this is the basis of structural forms of polymers and physical properties (starch, cellulose, glycogen etc)
To illustrate this:
The notation for the glycosidic linkage between the two sugars specifies which anomeric form of the sugar is involved in the bond and also specifies which carbon atoms of the two sugars are linked together.
For example two ways in which two α-D-glucose molecules can be linked together are α(1>4) and α(1>6). Firstly, the α anomeric carbon (C-l) of the first glucose molecule is joined in a glycosidic bond to the fourth carbon atom (C-4) of the second glucose molecule; or the C-1 of the first glucose molecule is linked to the C-6 of the second glucose .
Another important difference with respect to resulting polymers formed from these bonds - polysaccharides, in contrast to proteins and nucleic acids, form branched as well as linear polymers
α-Amylose is a linear polymer of several thousand glucose residues linked by α(1 >4) bonds. Note that although α-amylose is an isomer of cellulose, it has very different structural properties. This is because cellulose’s β-glycosidic linkages cause each successive glucose residue to flip 180° with respect to the preceding residue, so that the polymer assumes an easily packed, fully extended conformation.
The resulting linkage formed when α-amino acids polymerize, through the elimination of a water molecule is known as a peptide bond (sometimes called an amide bond):
Peptide bond (shown in red)
Glycosidic bonds between monosaccharide units are the basis for the formation of oligosaccharides and polysaccharides.
The glycosidic bond is therefore the carbohydrate analog of the peptide bond in proteins. (The bond in a nucleoside linking its ribose residue to its base is also a glycosidic bond)