Warmup Name two parts of the cell membrane

Warm-up • Name two parts of the cell membrane and explain the function of each. copyright cmassengale 1

The Plasma Membrane - Gateway to the Cell copyright cmassengale 2

Photograph of a Cell Membrane copyright cmassengale 3

Cell Membrane The cell membrane is flexible and allows a unicellular organism to move copyright cmassengale 4

Homeostasis • Balanced internal condition of cells • Also called equilibrium • Maintained by plasma membrane controlling what enters & leaves the cell copyright cmassengale 5

Functions of Plasma Membrane ü Protective barrier ü Regulate transport in & out of cell (selectively permeable) ü Allow cell recognition ü Provide anchoring sites for filaments of cytoskeleton copyright cmassengale 6

Functions of Plasma Membrane ü Provide a binding site for enzymes ü Interlocking surfaces bind cells together (junctions) üContains the cytoplasm (fluid in cell) copyright cmassengale 7

Structure of the Cell Membrane copyright cmassengale 8

Membrane Components Phospholipids Cholesterol Proteins (peripheral and integral) copyright cmassengale 9 Carbohydrates (glucose)

Phospholipids Make up the cell membrane Contains 2 fatty acid chains that are nonpolar Head is polar & contains a –PO 4 group & glycerol copyright cmassengale 10

FLUID MOSAIC MODEL FLUID- because individual phospholipids and proteins can move around freely within the layer, like it’s a liquid. MOSAIC- because of the pattern produced by the scattered protein molecules when the copyright cmassengale 11 membrane is viewed from above.

Cell Membrane Polar heads are hydrophilic “water loving” Nonpolar tails are hydrophobic “water fearing” Makes membrane “Selective” copyright cmassengale in what crosses 12

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Cell Membrane The cell membrane is Hydrophobic made of 2 layers of molecules pass phospholipid called the easily; hydrophilic lipid bilayer copyright cmassengale 14 DO NOT

Solubility • Materials that are soluble in lipids can pass through the cell membrane easily copyright cmassengale 15

Semipermeable Membrane Small molecules and larger hydrophobic molecules move through easily. e. g. O 2, CO 2, H 2 O copyright cmassengale 16

Semipermeable Membrane Ions, hydrophilic molecules larger than water, and large molecules such as proteins do not move through the membrane on their own. copyright cmassengale 17

Aquaporins • Water Channels • Protein pores used during OSMOSIS WATER MOLECULES copyright cmassengale 18

Osmosis in Red Blood Cells Isotonic Hypotonic copyright cmassengale Hypertonic 19

Warm-Up • Assume a cell is 80% salt and the solution outside is 15% water. • In what direction does the water move? This type of solution would be called? Will the cell be larger, smaller, or have no change? copyright cmassengale 20

Proteins Are Critical to Membrane Function copyright cmassengale 21

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 copyright cmassengale 22

Facilitated Diffusion Molecules will randomly move through the pores in Channel Proteins. copyright cmassengale 23

Facilitated Diffusion • 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. copyright cmassengale 24

Carrier Proteins • Other carrier proteins change shape to move materials across the cell membrane copyright cmassengale 25

Active Transport v. Requires energy or ATP v. Moves materials from LOW to HIGH concentration v. AGAINST concentration gradient copyright cmassengale 26

Sodium-Potassium Pump 3 Na+ pumped in for every 2 K+ pumped copyright cmassengale 27 out; creates a membrane potential

Moving the “Big Stuff” Exocytosis - moving things out. 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 copyright cmassengale 28 cells communicate with one another

Exocytosis Exocytic vesicle immediately after fusion with plasma membrane. copyright cmassengale 29

Moving the “Big Stuff” Large molecules move materials into the cell by one of three forms of endocytosis copyright cmassengale 30

Pinocytosis Most common form of endocytosis Takes in dissolved molecules as a vesicle copyright cmassengale 31.

Pinocytosis • Cell forms an invagination • Materials dissolve in water to be brought into cell • Called “Cell Drinking” copyright cmassengale 32

Example of Pinocytosis mature transport vesicle pinocytic vesicles forming copyright cmassengale Transport across a capillary cell (blue). 33

Receptor-Mediated Endocytosis Some integral proteins have receptors on their surface to recognize & take in hormones, cholesterol , etc. copyright cmassengale 34

Receptor-Mediated Endocytosis copyright cmassengale 35

Endocytosis – Phagocytosis Used to engulf large particles such as food, bacteria, etc. into vesicles Called “Cell Eating” copyright cmassengale 36

Phagocytosis About to Occur copyright cmassengale 37

Phagocytosis - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue) copyright cmassengale 38

Exocytosis The opposite of endocytosis is exocytosis. Large molecules that are manufactured in the cell are released through the cell membrane. Inside Cell copyright cmassengale Cell environment 39

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