Technically Sweet

Ever wondered how the sugar that you consume everyday serves many important functions in your body? Doesn't it sounds technically sweet as well? Read on...

Out of the many wonders of nature, sugar molecules are a must for human survival. Not that a sweet tongue cannot live without a chocolate brownie for long, but these sugars serve important biological functions when it comes to the human physiology.

Sugars are carbohydrates (remember that easy formula for glucose; 1:2:1?) and can be broadly classified into:

a) Monosaccharides: These are the simple sugars that contain 2-6 carbon atoms.
Example: Glucose (or grape sugar or corn sugar or dextrose), Fructose (fruit sugar), Galactose, Ribose

b) Disaccharides: These are composed of two simple sugars or monosaccharide units bound by a glycosidic linkage.
Example: Sucrose, Maltose, Lactose (milk sugar)

c) Oligosaccharides and Polysaccaharides: Longer units of monosaccharides bound by glycosidic bonds constitutes oligosaccharides and polysaccharides.

These long sugars are known as glycans and they can be attached to various other natural wonder molecules such as proteins, fats, inorganic compounds such as sulfur etc. The systematic study of these glycans is called as glycomics or the sweet science.

When the human genome project got completed, a lot of interest was generated glycomics. We began to understand that these sweet molecules play an important role in biological processes such as growth and development of mind and body, proper functioning of human organs and utmost, in the survival of organisms. Glycans also act as biochemical messengers transmitting important signals between cells and even help in maintaining a proper equilibrium in physiological functions. Thus, the effective cellular communication by glycans aids in the developmental process of cells and tissues.

Glycans seldom function on their own. They usually combine with lipids (fats) and proteins to form glycolipid and glycopeptide compounds, respectively. Their study is known as glycosylation. Based on the glycosylation patterns, glycans can be divided in six different classes.

1. Glycolipids
2. Hyaluronan
3. GPI Anchors
4. Glycosaminoglycans
5. O-Linked Glycans
6. N-Linked Glycans

Out of the above classes, N-linked and O-linked glycans are of great importance as they act as the signaling molecules in cell-cell interactions, help in protein stabilization and immune reactions which occur via glycan-glycan interactions.

Glycan Structures

Glycan functioning and their interaction depends on their structures. Determining the glycan structure is the first part of the glycomics riddle that the researchers at major universities across the world are trying to solve. Nuclear Magnetic Resonance (NMR) Spectroscopy, Mass Spectrometry, Analytical Chromatography which includes High Pressure Liquid Chromatography (HPLC) and Gas Chromatography(GC) are required for the complete structural characterization of glycans. There techniques break up the sweet molecules and determine the stereochemistry and bonding between the molecules.

Nuclear Magnetic Resonance (NMR) Spectroscopy: Information including the identity, anomeric configuration and the number of monosaccharides in a glycan can be easily determined by NMR. It reveals the stereochemistry of the monosaccharides involved in the complete sugar sequence and the nature of linkage. The major drawback associated with this technique is that it requires comparatively larger volume of sample for the structure determination.

Mass Spectrometry (MS): For systematic analysis of glycans, MS analysis is the approach. MS analysis determines the glycan masses and the composition. However, even this approach reveals limited structural information. Separation of fragments on the basis of their mass to charge ratio in the electrical or magnetic field is the fundamental principle of this technique.

Analytical Chromatographic Techniques: Before the sample containing glycans is introduced into a mass spectrometer, the different compounds present in the sample can be separated and analyzed with the help of chromatographic techniques. Direct analysis of glycopeptides can also be carried out without the need of derivitization through a technique called High Pressure Liquid Chromatography (HPLC).

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