The Key to Cellular Transport 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 Amount of cholesterol varies depending on the amount of fluidity needed in a membrane. Ranges from 25% of total lipid to 0%

Glycoproteins Proteins with carbohydrates attached – identifies the cell type -allows it to bind with other cells of the same type The carbohydrates are oligosaccharides (chains of no more 15 monosaccharides) Glycoproteins also are responsible for cell adhesion. Two cells with matching glycoproteins will bind together – allows the creation of tissues. Glycolipids exist as well they serve as recognition signals for cell interactions. The carbohydrate of glycolipids in cancer cells change. This signals to white blood cells that the cell needs to be destroyed

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