1 The Plasma Membrane The Plasma Membrane - Gateway to the Cell

2 Cell Membrane flexible The cell membrane is flexible and allows a unicellular organism to move

3 Homeostasis Balanced internal condition of cells Also called equilibrium Maintained by plasma membrane controlling what enters & leaves the cell

4 Functions of Plasma Membrane Protective barrier Regulate transport in & out of cell (selectively permeable) Allow cell recognition Provide anchoring sites for filaments of cytoskeleton

5 Functions of Plasma Membrane Provide a binding site for enzymes Interlocking surfaces bind cells together (junctions) Interlocking surfaces bind cells together (junctions) Contains the cytoplasm (fluid in cell) Contains the cytoplasm (fluid in cell)

6 Structure of the Cell Membrane

7 Cholesterol= another form of lipid that add flexibility to the membrane Glycocalyx= (aka glycoprotein) cell recognition Membrane Components

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9 Phospholipids Make up the cell membrane Contains 2 fatty acid chains that are nonpolar Head is polar & contains a phosphate group & glycerol

10 FLUID- because individual phospholipids and proteins can move side-to-side within the layer, like it’s a liquid. MOSAIC- because of the pattern produced by the scattered protein molecules when the membrane is viewed from above. FLUID MOSAIC MODEL

11 hydrophilic Polar heads are hydrophilic “water loving ” hydrophobic Nonpolar tails are hydrophobic “water fearing” Cell Membrane Makes membrane “Selective” in what crosses

12 Cell Membrane Hydrophobic molecules pass easily; hydrophilic DO NOT phospholipid bilayer The cell membrane is made of 2 layers of phospholipids called the lipid bilayer

13 Solubility Materials that are soluble in lipids can pass through the cell membrane easily

14 Small molecules and larger hydrophobic molecules move through easily. e.g. O 2, CO 2, H 2 O Semipermeable Membrane

15 Ions, hydrophilic molecules larger than water, and large molecules such as proteins do not move through the membrane on their own. Semipermeable Membrane

16 Proteins Are Critical to Membrane Function

17 Types of Transport Across Cell Membranes

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

What happens with a tea bag in water? What effects the rate of making tea? Passive Transport: 1.Diffusion: random movement of small molecules from an area of high concentration to an area of low concentration. 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

20 Passive Transport Simple Diffusion  Example: Oxygen or water diffusing into a cell and carbon dioxide diffusing out  Example: Oxygen or water diffusing into a cell and carbon dioxide diffusing out.  Name a scenario where this happens in the body.

21 Diffusion of Liquids What does the rate of diffusion depend on?

22 2. Facilitated diffusion: diffusion of large molecules through transport proteins Transport Proteins are specific – they “select” only certain molecules to cross the membrane Facilitated diffusion (Channel Protein) Diffusion (Lipid Bilayer) Passive Transport: AB

23 Passive Transport Facilitated diffusion Examples: Glucose or amino acids moving from blood into a cell.

24 Types of Transport Proteins Channel proteins are embedded in the cell membrane & have a pore for materials to cross Carrier proteins can change shape to move material from one side of the membrane to the other

25 Facilitated Diffusion Molecules will randomly move through the pores in Channel Proteins. copyright cmassengale

26 Facilitated Diffusion Some Carrier proteins do not extend through the membrane.Some Carrier proteins do not extend through the membrane. They bond and drag molecules through the lipid bilayer and release them on the opposite side.They bond and drag molecules through the lipid bilayer and release them on the opposite side.

27 Carrier Proteins Other carrier proteins change shape to move materials across the cell membraneOther carrier proteins change shape to move materials across the cell membrane

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

29 Aquaporins Water Channels Protein pores used during OSMOSIS WATER MOLECULES

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

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

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

33 Isotonic Solution NO NET MOVEMENT OF H 2 O (equal amounts entering & leaving) Hypotonic Solution CYTOLYSIS Hypertonic Solution PLASMOLYSIS

34 hypotonichypertonic isotonic hypertonicisotonic hypotonic

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 turgor 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.

Active Transport cell uses energy actively moves molecules to where they are needed Movement from an area of low concentration to an area of high concentration (Low  High) against the gradient Three Types:

Types of Active Transport 1. Protein Pumps - transport proteins that require energy to pump ions against the gradient 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!

38 Sodium-Potassium Pump 3 Na+ pumped in for every 2 K+ pumped out; creates a membrane potential

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

40Pinocytosis Most common form of endocytosis Most common form of endocytosis. Takes in dissolved molecules as a vesicle Takes in dissolved molecules as a vesicle.

41 Pinocytosis Cell forms an invaginationCell forms an invagination Materials dissolve in water to be brought into cellMaterials dissolve in water to be brought into cell Called “Cell Drinking”Called “Cell Drinking”

42 Receptor-Mediated Endocytosis Some integral proteins have receptors on their surface to recognize & take in hormones, cholesterol, etc.

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44 Endocytosis – Phagocytosis Used to engulf large particles such as food, bacteria, etc. into vesicles Called “Cell Eating”

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46 Phagocytosis About to Occur

47 Phagocytosis Phagocytosis - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue)

Types of Active Transport 3. Exocytosis: Forces material out of cell in bulk 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

49 Moving the “Big Stuff” Molecules are moved out of the cell by vesicles that fuse with the plasma membrane. This is how many hormones are secreted and how nerve cells communicate with one another This is how many hormones are secreted and how nerve cells communicate with one another.

50 Exocytosis The opposite of endocytosis is exocytosis. Large molecules that are manufactured in the cell are released through the cell membrane. Inside Cell Cell environment

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