The Cell Membrane 1

Cell membranes are composed of two phospholipid layers called a phosholipid bilayer. The cell membrane has two major functions: 1. Forms a boundary between inside and outside of the cell 2. Controls passage of materials into & out of the cell – Semi-permeable cell membrane outside cell inside cell 2

Phospholipid Composition 3 Parts – Polar Head – 1) Phosphate Group – 2) Glycerol – Nonpolar Tails – 3) Two chains of fatty acids Arrangement: – Outside: Polar heads Hydrophilic – Inside: Nonpolar Tails Hydrophobic 3

Phospholipid Bilayer

cell membrane The Fluid Mosaic Model – There are other molecules embedded in the membrane. Cholesterol strengthens Carbohydrate chains identify other cells Protein channels allow the passage of certain materials protein cholesterol protein carbohydrate chain protein channel 5

Semi-permeability. – The cell membrane is selectively permeable. Some molecules can cross the membrane while others cannot. 6

Chemical signals are transmitted across the cell membrane. – Receptors bind with ligands and change shape. – There are two types of receptors. intracellular receptor – The ligand binds to receptor INSIDE the cell 7

Chemical signals are transmitted across the cell membrane. – Receptors bind with ligands and change shape. – There are two types of receptors. intracellular receptor – Ligand binds to receptor INSIDE the cell membrane receptor – Ligand binds in the MEMBRANE 8