Cell Membranes Structure Function and Transport Cell Membranes

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.

Let’s Look at the Structure 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) Phospholipid Lipid Bilayer

B A C D F G H E

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

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

Cell Membranes 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? Pores

Types of Cellular Transport • Animations of Active Transport & Passive Transport • Weeee!! ! 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 to Low high low Low to High This is gonna be hard work!! high low

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 • Simple Diffusion Animation 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. http: //bio. winona. edu/berg/Free. htm

Passive Transport: Facilitated Diffusion A B Facilitated diffusion (Channel Protein) Diffusion (Lipid Bilayer) 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. Carrier Protein

Passive Transport: Facilitated Diffusion Glucose molecules Cellular Transport From a. High Concentration High • Channel Proteins animations Cell Membrane Low Concentration Through a Go to Section: Transport Protein channel Low

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

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 (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 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 • Osmosis Animations for isotonic, hypertonic, and hypotonic solutions 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)!

Hypertonic Solution • Osmosis Animations for isotonic, hypertonic, and hypotonic solutions 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? shrinks Result: Water moves from inside the cell into the solution: Cell can shrink drastically (Plasmolysis)!

• Isotonic Solution Osmosis Animations for isotonic, hypertonic, and hypotonic solutions 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!!!

What type of solution are these cells in? A B C hypertonic isotonic hypotonic

How Organisms Deal with Osmotic Pressure • Paramecium (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.