BIOLOGY Lecture Notes - Golden Pages 2003

1. THE CELL

Glycocalyx

Cell/30.html">The Plasma Membrane is surrounded by an outer coat known as the glycocalyx. The glycocalyx consists of complex carbohydrate-containing compounds. These CARBOHYDRATES are linked to Membrane Proteins, with their specific Composition and Structure being characteristic of each cell type.

The carbohydrate chains of these Glycoproteins play a crucial role in cell-Cell Recognition processes. Due to the high number of sugar residues and the diverse linkages between them, these macromolecules are capable of carrying a vast Amount of Information.

Sugar residues impart hydrophilicity to specific Regions of the membrane.

Erythrocyte Oligosaccharides exhibit the antigenic activity of the ABO and MN Blood Groups.

Most carbohydrates contain sialic and uronic acids, which give The Cell surface a negative electrical charge in a neutral medium. During The formation of intercellular contacts, Ca²⁺ ions appear to play an important role by bridging two negatively charged groups on the surfaces of adjacent Cells.

Carbohydrate residues:

1) are capable of modifying the PHYSICOCHEMICAL PROPERTIES OF Proteins;

2) are essential for proteins to acquire their correct conformation;

3) participate in the interaction of protein subunits;

4) help proteins find the proper orientation and anchor within The Lipid Bilayer;

5) protect proteins against proteolysis (enzymatic degradation);

6) viral oligosaccharides can mask the antigenic sites of proteins;

7) mediate intercellular contacts.