Topic 1.3: Membrane structure

1. 3. U2 List at least four functions of membrane bound proteins.

1. Receptor proteins communicate signals between the cells internal and external environments (i.e. hormone receptor) 2. Transport proteins move ions and molecules across the membrane (i.e. aquaporin transports water) 3. Enzymes catalyze reactions (i.e. ATP synthase) 4. Adhesion molecules anchor the cell to other cells (i.e. cadherin) 5. Recognition proteins identifiy the cell type (i.e. major histo-compatibility complex proteins)

1. 3. U1 Explain why phospholipids form bilayers in water, with reference to hydrophilic phosphate heads and two hydrophobic hydrocarbon tails.

Cell membranes are made up of a double layer of these phospholipid molecules. This is because in water the hydrophilic heads will face the water while the hydrophobic tails will be in the center because they face away from the water.

1. 3. U2 Contrast two types of transport proteins

Channel proteins are used for passive transport of molecules often shaped like pores/tunnels. Pump proteins are used for active transport of molecules.

1.3. U3 Describe the structural placement of cholesterol within the cell membrane.

Cholesterol fits between phospholipids in the cell membrane with its hydroxyl (-OH) group by the heads and the hydrophobic rings by the fatty acid tails.

1. 3. U3 Cholesterol is a component of animal cell membranes. Identify the structure of cholesterol in molecular diagrams

Cholesterol is a lipid that can be distinguished by its characteristic four-ring structure.

1.3. U2 Contrast the structure of integral and peripheral proteins

Peripheral proteins sit on the surface of have small sections that dip into the bilayer. Integral proteins have large sections embedded in the hydrophobic middle of the membrane. Some intergral proteins are "transmembrane" meaning they cross the membrane.

1.3.U2 Membrane proteins are diverse in terms of structure, position in the membranes and function. State the primary function of the cell membrane.

The cell membrane is semi-permeable and controls the movement of substances in and out of cells.

1. 3. U1 Define amphipathic and outline amphipathic properties of phospholipids.

amphipathic - molecule which has both hydrophobic and hydrophilic groups. They have hydrophilic heads and hydrophobic tails.

1. 3. U1 Define hydrophilic and hydrophobic

hydrophilic: water-loving hydrophobic: water repelling