CHAPTER 5: Cellular Processes Section Plasma Membrane Pgs Objective: I can explain the properties and “behavior” of the plasma membrane based on its structure and how it is put together.

Homeostasis (what is this?) Property of Life  Maintain a stable internal environment Cells have homeostasis  Take in food (maintain energy)  Get rid of waste (maintain cleanliness) Since cell (normally) has no mouth, absorbs through “skin” = Plasma membrane

Plasma Membrane Separates inside from outside Selects what goes in & out = selectively permeable  Structure (made of?):  Made of phospholipids  Forms (phospho)lipid bilayer  Arranged in a Fluid Mosaic Model

Phospholipid  Lipid Bilayer Polar hydrophilic heads (phosphate)  Faces watery environment (in/out of cell) Nonpolar hydrophobic tails (hydrocarbon)  Middle area to try to keep water (& other polar molecules from) passing through TWO Layers

Fluid Mosaic Model Phospholipids can move around and still maintain barrier (Fluid)  NOT connected, but stable (yet flexible) Other molecules can “float” and move in phospholipid bilayer (Mosaic) Inner Life of Cell – focus on phospholipids

Structure Details Cholesterol: steroid lipid to stabilize (make more rigid) Lots of proteins (stick through)  Polar A.A.  Nonpolar A.A.

Types of Membrane Proteins Some fixed, some movable Cell surface proteins  Can stick in or out (on one side)  Usually has a carbohydrate flag  Acts as a marker or identifier (communicates) Transmembrane proteins (channels/gates)  Almost always transports (act as gate)  Requires polar A.A. & non polar A.A. in chain Why? Can it move horizontally? Vertically?