Plasma Membrane – aka cell membrane THE FLUID MOSAIC MODEL Plasma Membrane – aka cell membrane What is it? What is it made of? What is its function?

Cell Membrane Structure: - A mosaic of lipids, proteins and carbohydrate, embedded in a fluid bilayer of phospholipids Cell Membrane Function: Controls what enters/exits a cell - maintains an internal balance called homeostasis b. Provides protection and support for the cell

Structure of the Cell Membrane Outside of cell Carbohydrate chains Proteins Lipid Bilayer Discuss integral and peripheral proteins Transport Protein Phospholipids Animations of membrane structure Inside of cell (cytoplasm) Go to Section:

Fluid Mosaic Model of the cell membrane Polar heads love water Membrane movement animation Non-polar tails hide from water. Carbohydrate cell markers selective permeability of membrane – presence of pores Proteins

HOW DOES THE MEMBRANE MOVE? A membrane is held in together by weak hydrophobic interactions. Most membrane lipids and some proteins can drift laterally within the membrane Molecules rarely flip transversely (flip-flop) across the membrane, because hydrophilic parts would have to cross the membrane’s hydrophobic core.

Why is fluidity important? Membrane must be fluid to work properly. Solidification may result in permeability changes Unsaturated hydrocarbon tails enhance membrane fluidity because kinks at the carbon-to-carbon double bonds hinder close packing of phospholipids.

What else helps to keep membrane fluidity? Cholesterol Cholesterol allows the cell membrane to stay fluid (esp. when temp drops), while at the same time keeping the cell from becoming too fluid (when temp rises) that it can no longer hold its shape