Passive and Active transport across a cell membrane REVIEW MEMBRANE TRANSPORT

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1 Passive and Active transport across a cell membrane REVIEW MEMBRANE TRANSPORT

2 Cell (plasma) membrane Thin, flexible barrier

3 Membranes also organize the interior of a cell. Cell organelles are defined by membranes.

4 Cell (plasma) Membrane What does it do for cell? Controls what goes in and out Every cell is covered by a membrane that controls what can enter and leave the cell. Protects/isolates Communicates Identification

5 Homeostasis Maintaining a Balance The plasma membrane is selectively permeable it will allow some things to pass through, while blocking other things. Cells must keep the proper concentration of nutrients and water and eliminate wastes.

6 Structure of the Plasma Membrane Lipid bilayer two sheets of lipids (phospholipids). Embedded with proteins and strengthened with cholesterol molecules.

7 Membrane Proteins Determine what particles can pass through the membrane. Serve as enzymes (may speed reactions). Act as markers that are recognized by chemicals and molecules from the inside and the outside of the cell.

8 Proteins Proteins help things get across membrane Some go all the way through like a channel Some use energy

9 Cell Function: transport osmosis and diffusion

10 homeostasis and transport Cell membranes help organisms maintain homeostasis by controlling what substances may enter or leave cells To stay alive, a cell must exchange materials with its environment These materials must cross the cell (plasma) membrane

11 Remember Cell membranes have protein channels Selectively permeable: Allows some molecules in and keeps other molecules out The structure helps it be selective!

12 the cell regulates movement in and out by two main methods: simple diffusion facilitated diffusion osmosis NO expenditure of Energy uses concentration gradient protein pumps endocytosis exocytosis expenditure of Energy does NOT use concentration gradient

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14 Biological membranes are SEMI-PERMEABLE -- A.K.A. Selectively permeable Cell membranes are picky

15 What diffuses across the membrane??? Small, uncharged (non-polar) molecules Examples: Carbon dioxide Oxygen

16 Types of Cellular Transport 111/animations/transport1.html Passive Transport cell does not use energy diffusion facilitated diffusion osmosis high Weeee!!! low Active Transport cell does use energy protein pumps exocytosis endocytosis high low This is gonna be hard work!!

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18 Diffusion Particles constantly move Collide randomly Spread out randomly Diffusion is moving from area of HIGH conc. to area of LOW conc. This is what we call the CONCENTRATION GRADIENT

19 diffusion Caused by Brownian motion (movement of particles because of the movement of their atoms). Continues until an equilibrium is reached (no gradient). Dynamic equilibrium particles continue to move freely and are evenly distributed. biology1111/animations/transport1.html

20 What happens when we reach equilibrium? Particles continue moving across membrane but in both directions! ***No more changes in concentration

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22 Osmosis Diffusion of water across a selectively permeable membrane. Occurs until water is balanced on both sides of the membrane.

23 How Osmosis works We have water molecules and some other molecules, let s say sugar If we have more solute concentration on one side of the membrane, then the water will diffuse across Membrane will let water thru but not sugar Water can move back and forth (not sugar)

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26 Cell Concentrations Hypertonic solutions more dissolved solute. Hypotonic solutions less dissolved solute. Isotonic solutions the same dissolved solute.

27 hypotonic solutions

28 hypertonic solutions

29 isotonic solutions

30 Why don t all our cells burst? What are our cells (animal) contained in? Fresh water? No..blood or other fluids, which are ISOTONIC The conc. Of sugars, salts, proteins and molecules in these fluids is the same as the conc. in the cell Bacteria and plant cells They DO come in contact with fresh water what do they have PROTECTING them? CELL WALL Prevent cells from expanding even when there s a lot of osmotic pressure But, cell walls are prone to injuries when there is too much osmotic pressure

31 Overcoming Osmosis Contractile vacuoles expel excess water from bacterial cells that live in water. Turgor pressure water pressure in a plant cell. Loss of turgor pressure causes wilting (plasmolysis).

32 Osmotic Pressure Central vacuole fills with water and exerts and out ward pressure on cell membrane and cell wall Cell wall does NOT allow cell to expand past a certain size Osmoregulation Osmoregulation means by which cells keep the concentration of cell cytoplasm or blood at a suitable concentration.

33 Problems in Plant Cell

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35 How do big molecules diffuse across a membrane so quickly if the membrane is selectively permeable?

36 Problems for diffusion Things too large (like Glucose!) Charged molecules and Polar molecules Positive/negative Opposites attract but likes do not These all present serious problems for things getting across membranes

37 Facilitated Diffusion What does facilitate mean? Proteins are the extra help escorts across the membrane We call these membrane proteins Protein channels Carrier proteins LIGAND receptor proteins

38 Facilitated Diffusion takes place through proteins, or assemblies of proteins, embedded in the plasma membrane Protein channels Carrier proteins LIGAND receptor proteins

39 Facilitated Diffusion (continued) FAST SPECIFIC Still diffusion so we only see it from high concentration to low Does NOT require energy

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41 What about when we want to go against the concentration? (From low concentration to high?)

42 What do we need??? ENERGY!!!!

43 Cellular Transport [2] Active transport energy is needed to move particles. Carrier proteins embedded proteins change shape to open and close passages across the membrane. Endocytosis taking something into the cell. Exocytosis expelling something from the cell.

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45 Exocytosis Exo- means Cyto means Sis means When cell releases large amounts of material Excretes stuff Membrane of vacuole surrounding particle inside cell fuses with the cell membrane The contents in vacuole are then forced out of the cell We see this in removal of water by contractile vacuoles

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