Lecture 13 Summary

Carbohydrates are the prime example of metabolic "fuel" for cells. The stepwise degradation of the monosaccharide glucose is a nearly universal pathway that yields biochemical energy in the form of adenosine triphosphate (ATP). Plants, in carrying out photosynthethesis, harvest the energy of sunlight by using it to convert carbon dioxide and water into carbohydrates. Glucose, fructose, and ribose are among the most common monosaccharides in biochemistry, a monosaccharide being a carbohydrate that cannot be broken down into simpler carbohydrate fragments. Polymeric forms of such simple carbohydrates are the complex carbohydrates. Furthermore, carbohydrate moeities are linked to or incorporated in other biomolecules, forming nucleotides, glycolipids, and glycoproteins. Glycobiology examines the roles of carbohydrates, glycoproteins, and other glycoconjugates in cellular and multicellular structure and function.

Glycobiology

Glycobiology is a relatively new branch of molecular and cell biology that is centered on the role of oligosaccharides (or glycans) as essential biochemical and structural components of eukaryotic cells. For the most part, glycans are attached to macromolecules at the surface of cells, and form a dense layer called the glycocalyx. Cell surface glycoproteins play important mediating roles in cell-matrix and cell-cell interactions. These roles are further elaborated in the context of complex multicellular organisms, where glycans participate in tissue and organ development and structure, and are involved in molecular mechanisms of pathogenesis, such as those occurring when a parasite gains access to a host.

The types of monosaccharide units common in animal glycans are sialic acids, hexoses, hexosamines, deoxyhexoses, pentoses, and uronic acids (Ref 2, §64). The term glycoconjugate is used to refer in general to glycans or oligosaccharides attached to another class of biological molecules, forming glycolipids and glycoproteins.

For more about glycobiology, see Ch.11 of Ref.1, starting at the bottom of p.312, and Ref.2 for a more comprehensive view.

Learning objectives

Page updated 8-16-09

References

1. Berg JM, Tymoczko JL, Stryer, L.  Biochemistry (6th edition)  Ch.11 - Carbohydrates (pp.303-325)
2. Varki A, Cummings R, Esko J, Freeze H, Hart G, Marth J (eds.) Essentials of Glycobiology (Cold Spring Harbor Press, 1999)