The Plasma Membrane

Thinking question: What do you know about the CELL MEMBRANE?

1. The PLASMA MEMBRANE’s overall function is to maintain cell HOMEOSTASIS. Thinking question: What is HOMEOSTASIS? A. Plasma Membrane

2. PLASMA MEMBRANE forms a thin, flexible boundary between a cell and its environment.

3. PLASMA MEMBRANES have a property called SELECTIVE PERMEABILITY. a 3. PLASMA MEMBRANES have a property called SELECTIVE PERMEABILITY. a. SELECTIVE PERMEABILITY - some substances pass through, others are kept out of the cell.

b. The MEMBRANE controls how, when, and how much substance enters and leave a cell.

-Ex: Similar to a fish net – the holes keep fish in, but let water pass through.

c. In doing this, the MEMBRANE ensures that what is required for HOMEOSTASIS enters/exits the cell.

1. The PLASMA MEMBRANE is made of a PHOSPHOLIPID BILAYER. a 1. The PLASMA MEMBRANE is made of a PHOSPHOLIPID BILAYER. a. Two layers of phospholipids, arranged tail to tail. B. Membrane Structure

2. A PHOSPHOLIPID has two parts: HYDROPHOBIC, non- polar fatty acid tails and HYDROPHILIC, polar head.

a. The head touches the water inside and outside of the cell a. The head touches the water inside and outside of the cell. The tails don’t.

3. PLASMA MEMBRANE contains other MACROMOLECULES. a 3. PLASMA MEMBRANE contains other MACROMOLECULES. a. Receptor PROTEINS transmit signals inside of the cell.

b. TRANSPORT PROTEINS move substances and wastes through the membrane.

c. CHOLESTEROL between the PHOSPHOLIPID tails keeps the membrane “fluid” or moving (so it doesn’t solidify)

d. CARBOHYDRATES on the membrane surface help the cell to “identify” itself to other cells.

4. CARBS and PROTEINS "float" in the PHOSPHOLIPID BILAYER. a 4. CARBS and PROTEINS "float" in the PHOSPHOLIPID BILAYER. a. This is called the FLUID MOSAIC MODEL. (FLUID = moving, MOSAIC = contains many parts, forms a pattern.)

b. The parts of the membrane are not bonded together – they constantly move around.

The Fluid Mosaic Model