A Closer Look at Cell Membranes

Transcription

1 A Closer Look at Cell Membranes

2 BOZEMAN VIDEO CELL MEMBRANES

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4 Lipid Bilayer Cell membranes consist of a containing Membrane is a continuous boundary layer that controls the flow of substances across it

5 parts parts fluid fluid one layer of lipids b one layer of lipids a cross-section through lipid bilayer Fig. 5.3, pg. 76

6 Model Every cell membrane has a mixed composition of phospholipids, glycolipids, sterols, and proteins KNOW THE CAMPBELL DIAGRAM CELL MEMBRANE MOSAIC

7 Fig. 5.4, pg. 77 Fluid Mosaic Model protein active transporter (calcium pump) passive transporter protein active transporter ( pump) receptor phospholipid cholesterol Lipid bilayer Cytoplasm proteins just beneath the plasma membrane Plasma Membrane

8 Fig. 5.5a, pg. 77 Studying Membranes Stepped Art

9 Overview of Membrane Proteins Proteins Proteins Fig. 5.6, p.78

10 Fig. 5.6, p.79 Overview of Membrane Proteins Proteins Proteins Transporters Transporters

11 Transport Proteins the lipid bilayer Interior is able to open to both sides Change when they interact with solute Play roles in active and passive transport

12 Concentration Gradient Means the number of molecules or ions in one region is than the number in another region In the absence of other forces, a substance moves from a region where it is concentrated to one where it s concentrated - AKA the gradient

13 Diffusion The net movement of like molecules or ions a concentration gradient Although molecules collide randomly, the net movement is from the place with the collisions (down gradient)

14 Diffusion Stepped Art Fig. 5.7a, p.80

15 Factors Affecting Diffusion Rate of concentration gradient Steeper gradient, faster diffusion Molecular Smaller molecules, diffusion Temperature Higher temperature, diffusion Electrical or pressure gradients

16 Membrane Crossing Mechanisms across lipid bilaye transport transport cytosis cytosis

17 Cell Membranes Show Selective Permeability Fig. 5-8, p.80

18 Membrane Crossing: Overview I Concentration gradient across cell membrane ATP Diffusion of lipid-soluble Substances across bilayer transport of watersoluble substances through protein; no energy input needed transport through ; requires input from ATP Fig. 5-9, p.81

19 Passive Transport Flow of solutes through the interior of passive transport proteins their concentration gradients Passive transport proteins allow solutes to move both ways Does not require any input

20 TYPES OF PASSIVE TRANSPORT diffusion that is helped out by (such as helping larger molecules pass)

21 Passive Transport glucose transporter solute (glucose) high low Stepped Art Fig. 5.10, p.80

22 Transport Net diffusion of solute is concentration gradient Transport protein must be activated (requires an ) ATP gives up phosphate to activate protein Binding of ATP changes protein shape and affinity for solute

23 TYPES OF ACTIVE TRANSPORT PUMP 3 move and allow 2 to ; needs net 1 ATP molecule to do this PUMP pushes H ions out of the membrane allowing them to ; generates ATP for the cell; used in This uses enzyme when molecules travel together across the membrane

24 Types of active transport Continued engulfing things into cell membrane; difficult for Ex: phagocytosis ( food) pinocytosis ( things) use of receptor proteins to help pull things into cell spitting things out of cell

25 Osmosis Diffusion of molecules across a selectively permeable membrane Direction of net flow is determined by water molecules protein molecules Side with the molecules has the lowest water concentration semipermeable membrane between two compartments

26 Osmosis p.84

27 Tonicity Refers to relative solute concentration of two fluids - having fewer solutes - having more solutes - having same amount

28 2% sucrose solution Tonicity and Osmosis 1 liter of distilled water 1 liter of 10% sucrose solution 1 liter of 2% sucrose solution Conditions Conditions Conditions Fig. 5-13, p.85

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30 DIALYSIS BAG % MASS CHANGE

31 Pressure and Osmosis Hydrostatic pressure Pressure exerted by fluid on the walls that contain it The greater the solute concentration of the fluid, the greater the hydrostatic pressure Osmotic pressure Amount of pressure necessary to prevent further increase of a solution s volume

32 Increase in Fluid Volume first compartmen t solution second compartmen t solution membrane permeable to water but not to solutes fluid volume in second compartmen t Fig. 5.14, p.85

33 ENDOCYTOSIS AND EXOCYTOSIS VIDEO

34 Endocytosis and Exocytosis Exocytosis: A cytoplasmic vesicle fuses with the plasma membrane and contents are released outside the cell 3 types: phagocytosis engulfs large molecules; difficult for plant cells to do (WHY??) pinocytosis engulfs small molecules receptor-mediated uses receptor membrane proteins to pull things in Endocytosis: A small patch of plasma membrane sinks inward and seals back on itself, forming a vesicle inside the cytoplasm membrane receptors often mediate this process

35 Macrophage engulfing Leishmania mexicana parasite macrophage Fig 5.17, p.87

36 Phagocytosis bacterium phagocytic vesicle Fig. 5-17b, p.87

37 Contractile Vacuole contractile vacuole filled contractile vacuole emptied Fig. 5.21, pg. 89

38 Plasmolysis Plasmolysis

39 adhesion protein passive transporter recognition protein receptor protein lipid bilayer cytoskeletal proteins cytoplasm active transporter (calcium pump) active transporter (ATPase pump) Fig. 5-19, p.88

40 BOZEMAN VIDEO CELL TRANSPORT ACROSS MEMBRANES AND ANIMATION