1. Introductory Questions #4
Name the major molecules that make up the cell membrane. How thick is the membrane?
How does the fluid mosaic model proposed by Singer & Nicholson (1972) compare with the Daveson & Danielli (1935) model?
Briefly explain how the membrane remains fluidic in lower temperatures?
What did the freeze fracture process and electron microscope reveal about the membrane?
How does cholesterol act as a “buffer” for the membrane? How does a hypotonic solution differ from a hypertonic solution?
What are the three forms of endocytosis? Explain how they are different.

2. Chapter 7~ Membrane Structure & Function Cellular Transport

3. Membrane Structure-Two Models Proposed
Amphipathic Lipids~ hydrophobic & hydrophilic regions
Singer-Nicholson:
fluid mosaic model
proposed in 1972
(Current model)

4. The Phospholipid Bilayer
The heads face outward and the tails face inward
In water, phospholipids form a stable bilayer
Water
Hydrophilic heads
Hydrophobic tails
Water
Figure 5.11B

5. Closer View of the Cell Membrane

6. Membrane Structure Approx. 10 nm thick Phospholipid Bilayer
-Amphipathic molecules
-Saturated and Unsaturated lipids
Proteins: integral &* peripheral
Cholesterol
-acts as a buffer
-increases membrane integrity
-increases fluidity

7. Membranes organize the chemical activities of cells
Membranes organize the chemical reactions making up metabolism  
Cytoplasm
Figure 5.10

8. Function of the Plasma Membrane
They control the flow of substances into and out of a cell
Membranes are selectively permeable
**Small, Nonpolar molecules easily pass through the membrane: O2, CO2, H2O, Hormones, Steroids
**Large, Charged do not pass through easily and must be
helped in. These molecules would include:
C6H12O6 , Proteins, and Ions
Membranes regulate chemical reactions and can hold teams of enzymes that function in metabolism

10. A Phospholipid

11. Membrane Phospholipids
Head
Phospholipids are the main structural components of membranes
They each have a hydrophilic head and two hydrophobic tails
Hydrophilic head
Hydrophobic tail

12. Membrane Structure - 2nd Look
Phospholipids~ membrane fluidity
Cholesterol~ membrane stabilization
“Mosaic” Structure~
Integral proteins~ transmembrane proteins
Peripheral proteins~ surface of membrane
Membrane carbohydrates ~ cell to cell recognition; oligosaccharides (cell markers); glycolipids; glycoproteins

13. Phospholipid Fluidity

14. Mouse-Human Hybrid Cell (Pg. 108)
David Frye & Micheal Edin (1970)

15. Fluidic Nature of the Membrane
To function properly:
Lipids must be in a state of optimal fluidity
Too much fluidity weakens the membrane
-not enough cholesterol
-too many unsaturated phospholipids
Also, the membrane cannot be too rigid because transport through the membrane is inhibited
Temperature changes can severely effect the membrane. HOW?

16. Freeze Fracture Method (Pg. 126)

18. Typical (integral)Transmembrane Protein

19. Proteins: Six Major Functions Observed- Pg. 128
C,D A G F G B

20. Lateral Transfer Across the Membrane
See Pgs (Ch. 11- Cell Communication)
Begins w/ signaling molecule called a Ligand
Ligands-examples are hormones & proteins
Involves several proteins:
Receptor (1st messenger) binds w/the ligand
Protein Kinases: an enzyme that transfers phosphate groups from ATP to a protein (uses ATP & moves phosphates)
G proteins & Adenylyl cyclase
Cyclic AMP: 2nd messengers

21. Lateral Transfer of Information Across the Membrane
Adenylyl Cyclase
Ligand
Enzymatic Rxns
G Protein
Receptor
cAMP
2nd messenger
Figure 5.13

22. Passive transport: Diffusion across a membrane
In passive transport, substances diffuse through membranes without work by the cell
They spread from areas of high concentration to areas of lower concentration
Molecule of dye
Membrane
EQUILIBRIUM
EQUILIBRIUM
Figure 5.14A & B

25. Membrane Traffic - (Pg. 132)
Diffusion~ tendency of molecules to move from
areas of high concentration to areas of low. Concentration gradient
Passive transport~ diffusion of a substance across a biological membrane
Osmosis~ the diffusion of water across a selectively permeable membrane

26. Osmosis is the passive transport of water
Hypotonic solution
Hypertonic solution
In osmosis, water travels from an area of lower solute concentration to an area of higher solute concentration
Selectively permeable membrane
Solute molecule
HYPOTONIC SOLUTION
HYPERTONIC SOLUTION
Water molecule
Selectively permeable membrane
Solute molecule with cluster of water molecules
NET FLOW OF WATER
Figure 5.15

27. Two Models of Facilitated Diffusion

28. Dialysis Tubing Experiment

29. OSMOSIS DEMONSTRATION (DIALYSIS BAGS)

30. Water balance between cells and their surroundings is crucial to organisms
Osmosis causes cells to shrink in a hypertonic solution and swell in a hypotonic solution
The control of water balance (osmoregulation) is essential for organisms
ISOTONIC SOLUTION
HYPOTONIC SOLUTION
HYPERTONIC SOLUTION
ANIMAL CELL
(1) Normal
(2) Lysing
(3) Shriveled
Plasma membrane
PLANT CELL
Figure 5.16
(4) Flaccid
(5) Turgid
(6) Shriveled

31. Osmosis and Animal Cells
NO CHANGE
CRENATION
WILL LYSE

32. OSMOSIS AND ANIMAL CELLS

33. The role of contractile vacuole in protists

34. OSMOSIS IN PLANT CELLS HYPOTONIC SOLUTION= NORMAL TURGOR PRESSURE
HYPERTONIC SOLUTION= PLASMOLYSIS

35. OSMOSIS IN PLANT CELLS (Elodea)
Plasmolyzed cells

36. An Artificial Cell Permeable to: monosaccharides & water Impermeable to: Disaccharides

37. Active Transport (Pg. 135)

38. Active transport in two solutes across a membrane
FLUID OUTSIDE CELL
Phosphorylated transport protein
Active transport in two solutes across a membrane
Transport protein
First solute 1
First solute, inside cell, binds to protein 2
ATP transfers phosphate to protein 3
Protein releases solute outside cell
Second solute 4
Second solute binds to protein 5
Phosphate detaches from protein 6
Protein releases second solute into cell
Figure 5.18

39. Common Type of Active Transport
Utilizes ATP and a protein
Moves substances against the concentration gradient
(Low to High)
Typical example is:
Na/K pump
(Observed in nerve cells)

40. Generating a Membrane Potential
Membrane potential: a charge difference across the membrane
Most commonly seen in nerve cells (sodium & potassium pump) – see pg 135
Achieved through actively pumping ions on one side of the membrane. (Na+ and K+)
All cells have a potential with a slight negative charge on the inside a positive charge on the outside. Why???

41. Specialized Transport
Transport proteins
Facilitated diffusion~ passage of molecules and ions with transport proteins across a membrane down the concentration gradient
Active transport~ movement of a substance against its concentration gradient with the help of cellular energy

42. Introductory Questions #4
Name the major molecules that make up the cell membrane. How thick is the membrane?
How does the fluid mosaic model proposed by Singer & Nicholson (1972) compare with the Daveson & Danielli (1935) model?
Briefly explain how the membrane remains fluidic in lower temperatures?
What did the freeze fracture process and electron microscope reveal about the membrane?
How does cholesterol act as a “buffer” for the membrane? How does a hypotonic solution differ from a hypertonic solution?
What are the three forms of endocytosis? Explain how they are different.

43. Introductory Questions #5
What did the freeze fracture process and electron microscope reveal about the membrane?
How is diffusion different from facilitative diffusion?
Name some factors that can affect diffusion rates of molecules.
Name the ions used to show how active transport works in a the cell membrane. What role does ATP play during this process?
What is the charge range difference across the membrane? Which side is positive and which side is negative?

44. Water Balance (pg. 133) Osmoregulation~ control of water balance
Hypertonic~ higher concentration of solutes
Hypotonic~ lower concentration of solutes
Isotonic~ equal concentrations of solutes
Cells with Walls:
Turgid (very firm)
Flaccid (limp)
Plasmolysis~ plasma membrane pulls away from cell wall

45. Endocytosis vs. Exocytosis
Endocytosis~ import of macromolecules by forming new vesicles with the plasma membrane
•phagocytosis
•pinocytosis
•receptor-mediated
Exocytosis~ secretion of macromolecules by the fusion of vesicles with the plasma membrane

46. EXOCYTOSIS To move large molecules or particles through a membrane
a vesicle may fuse with the membrane and expel its contents
FLUID OUTSIDE CELL
CYTOPLASM
Figure 5.19A

47. ENDOCYTOSIS
or the membrane may fold inward, trapping material from the outside (endocytosis)
Figure 5.19B

48. Three Types of Endocytosis

49. Material bound to receptor proteins
EXAMPLES OF ENDOCYTOSIS
Three kinds of endocytosis
Pseudopod of amoeba
Food being ingested
Plasma membrane
Material bound to receptor proteins
PIT
Cytoplasm
Figure 5.19C

50. CHOLESTEROL
Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors
Phospholipid outer layer
LDL PARTICLE
Receptor protein
Protein
Cholesterol
Plasma membrane
Vesicle
CYTOPLASM
Figure 5.20

51. The plasma membrane of an animal cell
Glycoprotein
Carbohydrate (of glycoprotein)
Fibers of the extracellular matrix
Glycolipid
Phospholipid
Cholesterol
Microfilaments of the cytoskeleton
Proteins
CYTOPLASM
Figure 5.12

52. Introductory Questions #5
What did the freeze fracture process and electron microscope reveal about the membrane?
How is diffusion different from facilitative diffusion?
Name some factors that can affect diffusion rates of molecules.
Name the ions used to show how active transport works in a the cell membrane. What role does ATP play during this process?
What is the charge range difference across the membrane? Which side is positive and which side is negative?
Name the three types of endocytosis observed in cells. (pg. 138)

53. Introductory Questions #4
Name the major molecules that make up the cell membrane. How thick is the membrane?
How does the fluid mosaic model proposed by Singer & Nicholson (1972) compare with the Daveson & Danielli (1935) model?
Briefly explain how the membrane remains fluidic in lower temperatures?
What did the freeze fracture process and electron microscope reveal about the membrane?
How does cholesterol act as a “buffer” for the membrane? How does a hypotonic solution differ from a hypertonic solution?
What are the three forms of endocytosis? Explain how they are different.