Transport Across a Membrane SEPT. 22, 2017

Transcription

1 Transport Across a Membrane SEPT. 22, 2017

2 Function (1) Passive Transport (2) Active Transport (3) Endocytosis/Exocytosis TOPICS

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4 Function

5 Function Maintains internal cell environment at a steady state, regardless of changes in the environment Acts as a selective barrier, regulating the movement of substances into and out of the cell

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7 Passive Membrane Transport SIMPLE DIFFUSION FACILITATED DIFFUSION OSMOSIS

8 Passive Transport Does not require energy Movement of molecules from area of [high] to [low]

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10 Dynamic Equilibrium Dynamic Equilibrium = the state in which continuous action results in balanced conditions

11 (1) Simple Diffusion Movement of molecules Across a semi-permeable membrane Down a concentration gradient From an area of [high] to [low] No energy required Simple transport W/O assistance of membrane proteins Occurs with small neutral molecules (O2, CO2)

12 (2) Facilitated Diffusion Similar to simple diffusion Across a semi-permeable membrane Passive transport Continues until equilibrium is achieved Difference is that a transport protein is involved Channel protein Carrier protein

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14 Transport Proteins Transport protein = An integral membrane protein that provides a pathway for molecules to cross a membrane 2 types: 1) channel 2) carrier

15 Channel Proteins Acts like a tunnel Moves by: Diffusion (passive transport down concentration gradient) Small dissolved charged molecules (e.g. ions)

16 Channel Proteins Aquaporins = specific type of channel protein that facilitate movement of water Question: Why can t water molecules cross a cell membrane by simple diffusion?

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18 Carrier Proteins Acts like a revolving door Undergo conformational change to allow molecules through Moves a variety of substances from charged particles to large uncharged molecules (e.g. glucose)

19 (3) Osmosis Diffusion of water Water moves from area of high [water] to low [water] Movement of water is in the opposite direction of the solute

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21 Osmotic Environments Hypotonic = hypo = less Hypertonic = hyper = more Isotonic = iso = same

22 Isotonic Isotonic = a solution that has the same [solute] as another solution Equal movement in and out of the cell

23 Hypotonic Hypotonic = a solution that has a lower [solute] than another solution Thus, higher [solute] inside the cell Which direction will the water move?

24 Water moves into the cell Cell expands Lysis = disintegration of cell by rupture of cell wall/membrane

25 Hypertonic Hypertonic = a solution that has a higher [solute] than another solution Thus, higher [solute] outside the cell Which direction will the water move?

26 Water moves out of the cell Cell shrinks

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28 Endocytosis/Exocytosis

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30 Endocytosis/Exocytosis Bulk membrane transport Molecules that are too large or too polar to pass through the membrane Folding of cell membrane to form a vesicle Vesicle = small, membrane-found organelle that may transport, store, or digest substances in a cell

31 (1) Endocytosis Endocytosis = Entry into the cell Phagocytosis Pinocytosis Receptor-mediated endocytosis

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33 (A) Phagocytosis Cellular eating Process by which living cells ingest other cells/large particles Found in simpler forms of life for feeding (e.g. amoebas) Used in higher order organisms as defense mechanism Phagocyte = white blood cell specialized for protecting the body

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35 (B) Pinocytosis Cellular drinking Ingestion of dissolved materials Occurs in most cell types Cell folds inwards to take in fluid containing desired substance

36 (C) Receptor-Mediated Intake of molecules that bind specifically to a receptor on the surface of the cell After binding, receptors collect into a pit coated with a network of proteins (clathrin) that reinforce the cytosol side

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39 (2) Exocytosis Endocytosis = Exiting the cell Movement of materials from the cell to the cell surface within membrane bound vesicles Secretory vesicles move through cytosol and contact plasma membrane à fuses à releases content Reverse of endocytosis

40 Exocytosis Secretion à release of waste, toxins, signaling molecules Cells lining the digestive tract à secrete mucus and digestive enzymes Plant cells secrete carbohydrates à build cell wall

41 Active Membrane Transport