THE CELL MEMBRANE The Key to Cellular Transport

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”

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

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

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

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

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

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

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

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

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