Question

Discuss the location, general characteristics, and relative abundance of glycolipids and glycoproteins in cellular membranes

Describe the general functions of the glycolipids and glycoproteins

Compare the mobility of membrane proteins to that of membrane lipids and explain the factors that influence the mobility of membrane proteins

Answer 1

1. Lipid and proteins on the cell membrane surface with short carbohydrate chains protruding out from the cell surface, are known as glycolipids and glycoproteins.

Glycoproteins are simply proteins with a carbohydrate attached to them. The sugars can be attached to a protein in two locations in the cell -- the endoplasmic reticulum and Golgi apparatus

Glycolipids comprise a hydrophobic lipid tail and one or more hydrophilic sugar groups linked by a glycosidic bond. It is generally found on the outer leaflet of cellular membranes. Glycolipids are found widely distributed throughout all cells and primarily localized to the plasma membrane.

Proteins are much larger than lipids, this percentage corresponds to about one protein molecule per every 50 to 100 molecules of lipid.

2. Both, glycolipids and glycoproteins act as receptors for molecules. Both of them stabilise the membrane by forming hydrogen bonds with surrounding water molecules. They also form the sites for binding hormones and antibodies and act as receptors for cell signalling. When the chemical binds to the receptor, it signals a response from the cell.

3. Lipids and membrane proteins diffuse rapidly in the plane of the membrane. The diffusion coefficient of lipid is about 1 μm² s^-1. A phospholipid molecule diffuses an average distance of 2 μm in 1 s. The magnitude of diffusion coefficient indicates that the viscosity of the membrane is about 100 times that of water.