The Plasma Membrane (Cell Membrane) The Fluid Mosaic Model

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Functions Separates the cell’s interior environment from the external environment. Regulates what enters and exits the cell. Communicates with other cells.

Selectively Permeable Based on size and solubility of molecule as well as specific protein channels.

Cell Membrane Structure Phospholipid bilayer Proteins Glycoproteins (protein + carbohydrate) Cholesterol molecules Isolation function Regulation and Communication Functions

The Phospholipid Bilayer Phospholipids arranged as a continuous double layer.

The Fluid Mosaic Model Fluidity of Membrane Mosaic-like Phospholipids and proteins move laterally. Components are not static. Mosaic-like Composed of many different macromolecules.

The Fluid Mosaic Model

Components Phospholipids Bilayer acts as a barrier. Hydrophobic nature causes membrane to be impermeable to water- soluble molecules. Phospholipids are not bonded to one another, so this double layer is quite FLUID with the individual molecules moving about easily. Phospholipid molecules have polar hydrophilic (water-loving) phosphate-based heads and nonpolar, hydrophobic (water-fearing) fatty acid tails. The plasma membrane is two layers, where the the tails become sandwiched so that the heads can interact with the water-based cytoplasm on one side and the water-based extra-cellular fluid on the other side.

Components Cholesterol Structural support – prevents fatty acids from tangling Regulates fluidity of membrane. High temps: makes outer membrane less fluid. Low temps: prevents the membrane from freezing and maintains membrane fluidity.

Components Membrane Protein Classification Integral Embedded (integrated) in the phospholipid bilayer Recognition proteins (special binding sites) Receptor proteins (receives signals) Transport proteins (channel or gated) Can be attached to other proteins Peripheral (smaller) Bound to Integral Proteins or embedded in membrane (one side only), attached to cytoskeleton Structural support

Components Membrane Proteins

Components Glycoproteins Carbohydrate chains attached to membrane proteins. On outer surface only. http://www.cs.stedwards.edu/chem/Chemistry/CHEM43/CHEM43/Glycoproteins/Glycoproteins.HTML Bind to molecules and guide them to Integral proteins (to transport or receive messages) Unique to each individual Very important as part of immune response system

Components Glycolipids Carbohydrate chains attached to the phospholipids. On outer surface only. Lipid and proteins on the cell membrane surface often have short carbohydrate chains protruding out from the cell surface, known as glycolipids and glycoproteins. They form hydrogen bonds with the water molecules surrounding the cell and thus help to stabilise membrane structure. However, more importantly, they are used as receptor molecules, binding with hormones or neurotransmitters to trigger a series of chemical reactions within the cell itself. Using insulin as an example, only some cells within the body (liver, muscles), have receptors