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 4
3.Structure of cell membrane Lipid Bilayer -2 layers of phospholipids a.Phosphate head is polar (water loving) b.Fatty acid tails non- polar (water fearing) c.Proteins embedded in membrane About Cell Membranes (continued) Phospholipid Lipid Bilayer 5
About Cell Membranes 1.All cells have a cell membrane 2.Functions: a.Controls what enters and exits the cell to maintain an internal balance called homeostasis b.Provides protection and support for the cell TEM picture of a real cell membrane. 6
8 Cell Membrane flexible The cell membrane is flexible and allows a unicellular organism to move
9 Homeostasis Balanced internal condition of cells Also called equilibrium Maintained by plasma membrane controlling what enters & leaves the cell
10 Functions of Plasma Membrane Protective barrier Regulate transport in & out of cell (selectively permeable) Allow cell recognition Provide anchoring sites for filaments of cytoskeleton
11 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)
15 Phospholipids Make up the cell membrane Contains 2 fatty acid chains that are nonpolar Head is polar & contains a –PO 4 group & glycerol
16 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
17 hydrophilic Polar heads are hydrophilic “water loving ” hydrophobic Nonpolar tails are hydrophobic “water fearing” Cell Membrane Makes membrane “Selective” in what crosses
28 Diffusion through a Membrane Cell membrane Solute moves DOWN concentration gradient (HIGH to LOW)
29 Osmosis Diffusion of water across a membraneDiffusion of water across a membrane Moves from HIGH water potential (low solute) to LOW water potential (high solute)Moves from HIGH water potential (low solute) to LOW water potential (high solute) Diffusion across a membrane Semipermeable membrane
30 Diffusion of H 2 O Across A Membrane High H 2 O potential Low solute concentration Low H 2 O potential High solute concentration
31 Aquaporins Water Channels Protein pores used during OSMOSIS WATER MOLECULES
32 Cell in Isotonic Solution CELL 10% NaCL 90% H 2 O 10% NaCL 90% H 2 O What is the direction of water movement? The cell is at _______________. equilibrium ENVIRONMENT NO NET MOVEMENT
33 Cell in Hypotonic Solution CELL 10% NaCL 90% H 2 O 20% NaCL 80% H 2 O What is the direction of water movement?
34 Cell in Hypertonic Solution CELL 15% NaCL 85% H 2 O 5% NaCL 95% H 2 O What is the direction of water movement? ENVIRONMENT
41 Three Forms of Transport Across the Membrane
42 Passive Transport Simple Diffusion Doesn’t require energy Moves high to low concentration 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.
43 Passive Transport Facilitated diffusion Doesn’t require energy Uses transport proteins to move high to low concentration Examples: Glucose or amino acids moving from blood into a cell.
45 These are carrier proteins. They do not extend through the membrane. They bond and drag molecules through the bilipid layer and release them on the opposite side.
46 Sodium-Potassium Pump 3 Na+ pumped in for every 2 K+ pumped out; creates a membrane potential
47 Cotransport also uses the process of diffusion. In this case a molecule that is moving naturally into the cell through diffusion is used to drag another molecule into the cell. In this example glucose hitches a ride with sodium.
48 Receptor Proteins These proteins are used in intercellular communication. In this animation you can see the a hormone binding to the receptor. This causes the receptor protein release a signal to perform some action.
49 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
50 Facilitated Diffusion Molecules will randomly move through the pores in Channel Proteins.
51 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.
52 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
53 Active Transport Requires energy or ATP Moves materials from LOW to HIGH concentration AGAINST concentration gradient
54 Active transport Examples: Pumping Na + (sodium ions) out and K + (potassium ions) in against strong concentration gradients. Called Na+-K+ Pump
58 Moving the “Big Stuff” Molecules are moved out of the cell by vesicles that fuse with the plasma membrane. Exocytosis Exocytosis - moving things out. 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.
59 Exocytosis Exocytic vesicle immediately after fusion with plasma membrane.
60 Moving the “Big Stuff” Large molecules move materials into the cell by one of three forms of endocytosis Large molecules move materials into the cell by one of three forms of endocytosis.
61Pinocytosis Most common form of endocytosis Most common form of endocytosis. Takes in dissolved molecules as a vesicle Takes in dissolved molecules as a vesicle.
62 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”
63 Example of Pinocytosis pinocytic vesicles forming mature transport vesicle Transport across a capillary cell (blue).
64 Receptor-Mediated Endocytosis Some integral proteins have receptors on their surface to recognize & take in hormones, cholesterol, etc.
73 Cotransport also uses the process of diffusion. In this case a molecule that is moving naturally into the cell through diffusion is used to drag another molecule into the cell. In this example glucose hitches a ride with sodium.
74 Exocytosis The opposite of endocytosis is exocytosis. Large molecules that are manufactured in the cell are released through the cell membrane.