Cell Membranes Structure, Function and Transport

Cell Membranes ALL CELLS HAVE A CELL MEMBRANE Why do all cells need a cell membrane? Functions: 1. Controls what enters and exits 2. Provides protection and support for the cell TEM picture of a real cell membrane.

Lipid Bilayer – 2 layers of phospholipids (chocolate chip ice cream sandwich) a.Fatty acid tails (ice cream) b.Phosphate head (cookie) c.Proteins- embedded in membrane: (chocolate chips) d.Carbohydrates-sticking out (label) Let’s Look at the Structure Phospholipid Lipid Bilayer

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Proteins Membrane movement animation Polar heads love water & dissolve. Non-polar tails hide from water. Carbohydrate cell markers Fluid Mosaic Model of the cell membrane

Outside of cell Inside of cell (cytoplasm) Lipid Bilayer Proteins Transport Protein Phospholipids Carbohydrate chains Structure of the Cell Membrane Go to Section: Animations of membrane structure

Cell membranes allow some molecules to move through but not others. This is called being Selectively Permeable. How is a cell membrane like a screen door? Cell Membranes Pores

Types of Cellular Transport Passive Transport cell doesn’t use energy 1.Diffusion 2.Facilitated Diffusion 3.Osmosis Active Transport cell does use energy 1.Protein Pumps 2.Endocytosis 3.Exocytosis high low This is gonna be hard work!! high low Weeee!! ! Animations of Active Transport & Passive TransportAnimations High to Low Low to High

Traits of Passive Transport 1.Cell uses no energy 2.Molecules move randomly 3.Molecules spread out from an area of high concentration to an area of low concentration. HIGH  LOW 4.Continues until all molecules are evenly spaced (equilibrium)-Note: molecules will still move around but stay spread out.

3 Types of Passive Transport 1.Diffusion -solutes move 2.Facilitated Diffusion – solutes move with the help of transport proteins 3.Osmosis – water moves HIGH  LOW

Passive Transport: Diffusion Random movement of particles (particles are always bumping into each other) from an area of high concentration to an area of low concentration. (High  Low) Particles move through pores (spaces) in cell membrane Molecules will still move around but stay spread out. Simple Diffusion AnimationSimple Diffusion Animation

Movement of specific particles through Transport Proteins Transport Proteins are specific – they “select” only certain molecules to cross the membrane Transports larger or charged molecules that can’t move through pores. Facilitated diffusion (Channel Protein) Diffusion (Lipid Bilayer) Passive Transport: Facilitated Diffusion Carrier Protein AB

High Concentration Low Concentration Cell Membrane Glucose molecules Protein channel Passive Transport: Facilitated Diffusion Go to Section: Transport Protein Through a  Cellular Transport From a- High Low Channel Proteins animationsChannel Proteins

diffusion of WATER ONLY through a selectively permeable membrane Water moves from high to low concentrations Continues until concentration reaches equilibrium Water moves freely through pores. Solute (green) to large to move across. Osmosis Osmosis animation Passive Transport: Osmosis

Traits of Active Transport 1.Cell uses energy 2.Actively moves molecules to where they are needed 3.Movement from an area of low concentration to an area of high concentration LOW  HIGH 4.Doesn’t move toward equilibrium

3 Types of Active Transport Protein Pumps-move solutes through membrane channels in either direction Endocytosis-move materials out Exocytosis-move materials in LOW  HIGH

Types of Active Transport Protein Pumps - transport proteins that require energy to do work Example: Sodium / Potassium Pumps are important in nerve responses. Sodium Potassium Pumps Sodium Potassium Pumps (Active Transport using proteins) Protein changes shape to move molecules: this requires energy!

Types of Active Transport Endocytosis (endo=in): taking bulky material into a cell A.K.A.“cell eating” Cell membrane in-folds around food particle forms food vacuole This is how white blood cells eat bacteria!

Types of Active Transport Exocytosis (exo=out): Forces material out of cell Membrane surrounding the material and forms a vacuole This fuses with cell membrane Materials are forces out Hormones or wastes released from cell Endocytosis & Exocytosis Endocytosis & Exocytosis animations

Effects of Osmosis on Life REMEMBER: Osmosis is the diffusion of water through a selectively permeable membrane HIGH CONC  LOW CONC This is great is most cases but can also cause some BIG PROBLEMS!

Hypotonic Solution Hypotonic: The solution the cell is found in has a lower concentration of solutes (hypo-low) and a higher concentration of water than inside the cell. (Low solute = High water) Which direction does the water move? Result: Water moves from the solution to inside the cell): Cell Swells and can burst open (cytolysis)! Osmosis Animations for isotonic, hypertonic, and hypotonic solutionsOsmosis

Hypertonic Solution Hypertonic: The solution the cell is found in has a higher concentration of solutes (hyper-high) and a lower concentration of water than inside the cell. (High solute = Low water) Which direction does the water move? Result: Water moves from inside the cell into the solution: Cell can shrink drastically (Plasmolysis)! Osmosis Animations for isotonic, hypertonic, and hypotonic solutionsOsmosis shrinks

Isotonic Solution Isotonic: The concentration of solutes in the solution the cell is found in is equal (iso-same) to the concentration of solutes inside the cell. Which directions does the water move? Result: Water moves equally in both directions and the cell remains same size! (Dynamic Equilibrium) This condition maintains HOMEOSTASIS!!! Osmosis Animations for isotonic, hypertonic, and hypotonic solutionsOsmosis

What type of solution are these cells in ? A CB hypertonicisotonichypotonic

How Organisms Deal with Osmotic Pressure Paramecium (protist) removing excess water videoParamecium (protist) removing excess water video Bacteria and plants have cell walls that prevent them from over-expanding. In plants the pressure exerted on the cell wall is called tugor pressure. A protist like paramecium has contractile vacuoles that collect water flowing in and pump it out to prevent them from over-expanding. Salt water fish pump salt out of their specialized gills so they do not dehydrate. Animal cells are bathed in blood. Kidneys keep the blood isotonic by remove excess salt and water.