Topic 3 Cell Membrane

Phospholipids Primary component of the cell membrane OBJ 9 Phospholipids Primary component of the cell membrane Phosphate - Hydrophilic head Fatty Acids - Hydrophobic tails

How do phospholipids interact with water?     OBJ 9 How do phospholipids interact with water? Spontaneous formation!

Detailed view of an animal cell membrane OBJ 10 Phospholipid

Cell Membrane – Structure and Function OBJ 10 Cell membrane also called Plasma membrane Phospholipids Bilayer Main component of the cell membrane Hydrophilic head points in and out Hydrophobic tails Carbohydrates Cell to cell recognition Extracellular Connected to proteins and/or lipids Glycoproteins Glycolipids Cholesterol Imbedded into the phospholipid bilayer Increases fluidity of membrane

Cell Membrane – Structure and Function (continued) Obj 10 Cell Membrane – Structure and Function (continued) Proteins Glycoproteins – cell to cell recognition Important in immune system Junctions between cells Enzymes - imbedded in membrane Receptors – trigger a chain reaction inside the cell Transport proteins Integrins – attach to cytoskeleton Connect cells to cells or cells to the extracellular matrix

Cell membrane – TEM image OBJ 10 Cell membrane – TEM image Start here G block

Transmembrane protein or integral protein OBJ 10 Transmembrane protein or integral protein Spans the width of the bilayer Often are transport proteins

Fluid Mosaic Model Phospholipids bilayer is in constant motion. Obj 11,12 Phospholipids bilayer is in constant motion. Cholesterol - imbedded in membrane - adds to fluidity Selectively permeable Some molecules can pass though because of the fluidity

Cell membranes – “the gate keeper of the cell” What does a cell need to bring in? What does a cell need to get rid of?

Selective Permeability OBJ 12 Only some substances can pass into the cell What limits it? Polarity of molecule Size of molecule Charge of molecule Size Passes freely through the membrane Needs a special protein transporter Needs to use other methods to pass through Polarity and Size Nonpolar molecules (steroids, N2, O2) Some very small polar molecules (water, ethanol, etc) Small polar molecules (amino acids, sugars, etc) Large polar molecules (proteins) Electric Charge No charge Charged atoms (H+ or Ca+)