The Cell Membrane What do you notice about the picture below? What parts can you name? Do you know their functions?

Cell Membrane 8,000 membranes to equal one sheet of paper

Functions of Cell Membrane 1.Control what enters and exits the cell 2.Help cell keep its shape 3.Communicate with other cells

Selectively Permeable? WHY? The structure of the membrane makes it determine what substances can enter and not enter! Controls traffic in & out of the cell –Selectively permeable - allows some substances to cross more easily than others. –WHY? Hydrophobic tails vs hydrophilic heads

What has to get in and out of the cell? OxygenCO2 GlucoseWaste Amino acidnew proteins Vitamins water

Parts of the Cell Membrane 1.Phospholipids 3. Proteins 2.Cholesterol 4. Carbohydrates

Phospholipids Fatty acid Phosphate 1. Fatty acid tails –hydrophobic 2. Phosphate group 3. Glycerol –Hydrophilic Aaaah, one of those structure–function examples

Why are the phosolipids arrange this way? Heads - hydrophilic face outward Tails - Hydrophobic face inward Water surrounds the cell and is inside the cell. Hydrophilic must face outward. Arranged as a bilayer

The Arrangement of the Phosolipids determine how particles pass through the cell membrane ? If a particle is small and not charged then it can move straight through the membrane. If the particle is large and charged, then it has to move through the cell proteins. Aquaporins - protein channel that water moves through.

5 Functions of Proteins 1.Pumps material through the membrane 2.Channels 3. Proteins on the inside of cell. Attach to cytoskeleton. Help with structure!! 4. Receptors – Carbohydrates are attached to proteins! 5. Enzymes!

Membrane carbohydrates Play a key role in cell-cell recognition –ability of a cell to distinguish one cell from another antigens –important in organ & tissue development –basis for rejection of foreign cells by immune system

Function of Cholesterol Strengthen cell membrane – phosolipids are not bonded so membrane is not strong!

Fluid Mosaic Model Describes the characteristics of the cell membrane 1.Cell membrane is flexible not rigid. Acts as a fluid. The double bonds between the tails keep them from attaching because of kinks. 2.Cell membrane is constructed for many different parts.

Selective Permeability Cell membrane allows some materials in and others not. Homeostasis: Cell maintenance of stable internal conditions in a changing environment. How a molecules moves across a membrane depends on the size, polarity, and concentration of the molecules.

Do you Agree that Molecules Must Move Across Membrane? VIDEO – molecules moving This is called Brownian Movement

Molecules are constantly moving!! You must understand that molecules are constantly moving. The more energy added the faster they move. Move from an area of a higher concentration to an area of lower concentration across the membrane.

3 Ways Particles Move Across Membrane!! 1. Small and non charged particles can just move through the membrane. 2. Small polar molecules move through the protein channels. 3. Large particles move in vesicles or pumps.

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

Passive Transport The energy behind this type of transport is caused by a CONCENTRATION GRADIENT!!!

Concentration Gradient The difference in the concentration of molecules in two different regions. Can be a room or a cell!!!! Equilibrium: molecules will continue to move until equal on both sides.

Transport summary simple diffusion facilitated diffusion active transport ATP

Passive Transport – movement of molecules across cell membrane without energy. 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) CAN BE THROUGH A CHANNEL!!!

3 Types of Passive Transport 1.Diffusion 2.Facilitative Diffusion – diffusion with the help of transport proteins 3.Osmosis – diffusion of water through aquaporin.

Passive Transport: 1. Diffusion 1.Diffusion: random movement of particles from an area of high concentration to an area of low concentration. (High to Low) Diffusion continues until all molecules are evenly spaced (equilibrium is reached)-Note: molecules will still move around but stay spread out. Simple Diffusion AnimationSimple Diffusion Animation

Diffusion Move from HIGH to LOW concentration –“passive transport” –no energy needed –Small and non charged –Straight through membrane diffusionosmosis

Diffusion through phospholipid bilayer What molecules can get through directly? –fats & other lipids –SMALL & NONPOLAR inside cell outside cell lipid salt aa H2OH2O sugar NH 3 What molecules can NOT get through directly? –polar molecules H 2 O –ions salts, ammonia –large molecules starches, proteins

2.Osmosis: facilitated diffusion of water through a selectively permeable membrane Water moves from high to low concentrations AQUAPORIN Water moves freely through pores. Solute (green) to large to move across. Osmosis Osmosis animation Passive Transport: 2. Osmosis

Effects of Osmosis on Life Osmosis- diffusion of water through a selectively permeable membrane Water is so small and there is so much of it the cell can’t control it’s movement through the cell membrane.

Aquaporins Water moves rapidly into & out of cells –evidence that there were water channels 1991 | 2003 Peter Agre John Hopkins Roderick MacKinnon Rockefeller

Concentration of water Direction of water movement is determined by the amount of solution in or out of the cell because water is not all that the cell contains.

3 Types of Solutions For a Cell 1. Hypertonic - more solute, less water. More water inside cell; it leaves 2. Hypotonic - less solute, more water. More water outside cell; water enters 3. Isotonic - equal solute, equal water Equal – net movement equal!

Hypotonic Solution Hypotonic: The solution has a lower concentration of solutes and a higher concentration of water than inside the cell. (Low solute; High water) Result: Water moves from the solution to inside the cell): Cell Swells and bursts open (cytolysis)! Osmosis Animations for isotonic, hypertonic, and hypotonic solutionsOsmosis

Managing water balance Hypotonic –a cell in fresh water example: Paramecium problem: gains water, swells & can burst –water continually enters Paramecium cell solution: contractile vacuole –pumps water out of cell –ATP –plant cells turgid freshwater ATP

freshwaterbalancedsaltwater Managing water balance Cell survival depends on balancing water uptake & loss

Hypertonic Solution Hypertonic: The solution has a higher concentration of solutes and a lower concentration of water than inside the cell. (High solute; Low water) Result: Water moves from inside the cell into the solution: Cell shrinks (Plasmolysis)! Osmosis Animations for isotonic, hypertonic, and hypotonic solutionsOsmosis shrinks

Managing water balance Hypertonic –a cell in salt water example: shellfish problem: lose water & die solution: take up water or pump out salt –plant cells plasmolysis = wilt saltwater

Isotonic Solution Isotonic: The concentration of solutes in the solution is equal to the concentration of solutes inside the cell. Result: Water moves equally in both directions and the cell remains same size! (Dynamic Equilibrium) Osmosis Animations for isotonic, hypertonic, and hypotonic solutionsOsmosis

Managing water balance Isotonic –animal cell immersed in mild salt solution example: blood cells in blood plasma problem: none –no net movement of water »flows across membrane equally, in both directions –volume of cell is stable balanced

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.

2. Facilitated diffusion: diffusion of specific particles through transport proteins found in the membrane a.Transport Proteins are specific – they “select” only certain molecules to cross the membrane b.Transports larger or charged molecules Facilitated diffusion (Channel Protein) Diffusion (Lipid Bilayer) Passive Transport: Facilitated Diffusion Carrier Protein AB

Facilitated Diffusion Diffusion through protein channels –channels move specific molecules across cell membrane –no energy needed “The Bouncer” open channel = fast transport facilitated = with help high low

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

Active Transport “The Doorman” conformational change 1. Cells may need to move molecules against concentration gradient –shape change transports solute from one side of membrane to other –protein “pump” –“costs” energy = ATP ATP low high

Active Transport 1. cell uses energy 2. Movement from an area of low concentration to an area of high concentration AGAINST THE CONCENTRATION GRADIENT! (Low  High) 3. Move molecules in vesicles that are too large!

Types of Active Transport 1. 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 2. Endocytosis: taking bulky material into a cell in a vesicle. Uses energy Cell membrane in-folds around food particle “cell eating” forms food vacuole & digests food This is how white blood cells eat bacteria!

Endocytosis phagocytosis pinocytosis receptor-mediated endocytosis fuse with lysosome for digestion non-specific process triggered by molecular signal

Types of Active Transport 3. Exocytosis: Forces material out of cell in bulk in a vesicle membrane surrounding the material fuses with cell membrane Cell changes shape – requires energy EX: Hormones or wastes released from cell Endocytosis & Exocytosis Endocytosis & Exocytosis animations

How about large molecules? Moving large molecules into & out of cell –through vesicles & vacuoles 1. endocytosis phagocytosis = “cellular eating” pinocytosis = “cellular drinking” 2. exocytosis exocytosis