1. THE CELL MEMBRANE The Key to Cellular Transport

2. Some Membrane Terms  Many substances can diffuse across biological membranes, but some are too large or too strongly charged to cross the lipid bilayer.  If a substance is able to diffuse across a membrane, the membrane is said to be permeable to it.  A membrane is impermeable to substances that cannot pass across it.  Most biological membranes are selectively permeable, meaning that some substances can pass across them and others cannot.

3. Characteristics of the Cell Membrane  Made of phospholipids – arranged in two layers called a bilayer  Selectively permeable - it controls “selects” what can enter or leave the cell -some materials are allowed through others aren’t  Fluid Mosaic Model - made of different molecules – phospholipids, proteins, cholesterol - the molecules aren’t static but can move “fluid”

4. Lipid bi-layer – the heart of the membrane  Phospholipids are arranged into 2 layers - called a bilayer

5. Phospholipids: Phosphate Heads  Polar/hydrophillic – attracted to water and charged particles

6. Phospholipids: Lipid Tails  Nonpolar/hydrophobic – repel water and charged particles

7. Cholesterol  Found in bilayer – helps to hold the membrane together while adding to fluidity of the membrane

8. Glycoproteins  Proteins with carbohydrates attached – identifies the cell type -allows it to bind with other cells of the same type

9. Receptor Proteins  recognize and bind with substances outside of the cell, causing changes inside the cell

10. Enzymes  Allow reactions to occur- light reactions and ETS occur with enzymes in membrane

11. Transport Proteins  Proteins that extend across the membrane – provide a way for large or charged molecules to cross the membrane

12. Types of Transport Proteins  Ion Channels- allow certain charged particles to cross the membrane – passive transport  Carrier Proteins – bind to a specific molecule and carry it across the membrane - facilitated diffusion – proteins carry molecules with the concentration gradient /no cellular energy is required - active transport – proteins carry molecules against the concentration gradient/ cellular energy is required