1. CH. 5 CELL MEMBRANE AND TRANSPORT
A Closer Look at Cell Membranes

2. BOZEMAN VIDEO—CELL MEMBRANES

3. http://www. youtube. com/watch. v=y31DlJ6uGgE http://www. youtube

4. Lipid Bilayer
Cell membranes consist of a lipid bilayer containing different proteins
Membrane is a continuous boundary layer that selectively controls the flow of substances across it

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

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

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

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

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

10. Overview of Membrane Proteins
Receptor
Proteins
Recognition
Proteins
Passive
Transporters
Active
Transporters
Fig. 5.6, p.79

11. Transport Proteins Span the lipid bilayer
Interior is able to open to both sides
Change shape 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 different than the number in another region
In the absence of other forces, a substance moves from a region where it is more concentrated to one one where it’s less concentrated - “down” gradient

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

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

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

16. Membrane Crossing Mechanisms
Diffusion across lipid bilayer Passive transport Active transport Endocytosis Exocytosis

17. Cell Membranes Show Selective Permeability
oxygen, carbon
dioxide, and other
small, nonpolar
molecules; some
water molecules
glucose and other large,
polar, water-soluble
molecules; ions (e.g.,
H+, Na+, K+, Ca++,
Cl–); water molecules
Fig. 5-8, p.80

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

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

20. TYPES OF PASSIVE TRANSPORT
DIFFUSION
FACILITATED DIFFUSION—diffusion that is “helped out” by membrane transport proteins (such as helping larger molecules pass)

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

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

23. TYPES OF ACTIVE TRANSPORT
SODIUM-POTASSIUM PUMP—3 Na move out and allow 2 K to enter; needs net 1 ATP molecule to dothis
PROTON PUMP– pushes H ions out of the membrane allowing them to eventually diffuse back in; generates ATP for the cell; used in cell respiration
This uses ATP synthase enzyme
COTRANSPORT– when molecules travel together across the membrane

24. Types of active transport Continued
Endocytosis—”engulfing “things into cell membrane; difficult for plants to do
Ex: white blood cells engulfing bacteria—to fight infections
phagocytosis (large food)
pinocytosis (small things)
Receptor-mediated endocytosis—use of receptor proteins to help pull things into cell
Exocytosis—”spitting” things out of cell

25. Osmosis
Diffusion of water molecules across a selectively permeable membrane
Direction of net flow is determined by water concentration gradient
Side with the most solute molecules has the lowest water concentration

26. Osmosis
p.84

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

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

30. DIALYSIS BAG % MASS CHANGE

31. Pressure and Osmosis Hydrostatic pressure Osmotic 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 compartment
second compartment
hypotonic
solution
hypertonic
solution
membrane permeable to
water but not to solutes
fluid volume rises in second compartment
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. active transporter (calcium pump) active transporter (ATPase pump)
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