1. Lecture Cell Chapters 5 and 6 Biological Membranes and
Cell Communication

2. Membrane structure, I Selective permeability
Amphipathic~ hydrophobic & hydrophilic regions
Singer-Nicolson: fluid mosaic model

3. Carbohydrate chains Glycoprotein Carbohydrate chain
Extracellular fluid
Hydrophobic
Hydrophilic
Glycolipid
Figure 5.6: Detailed structure of the plasma membrane.
Although the lipid bilayer consists mainly of phospholipids, other lipids, such as cholesterol and glycolipids, are present. Peripheral proteins are loosely associated with the bilayer, whereas integral proteins are tightly bound. The integral proteins shown here are transmembrane proteins that extend through the bilayer. They have hydrophilic regions on both sides of the bilayer, connected by a membrane-spanning α-helix. Glycolipids (carbohydrates attached to lipids) and glycoproteins (carbohydrates attached to proteins) are exposed on the extracellular surface; they play roles in cell recognition and adhesion to other cells.
Cholesterol
Hydrophilic
α-helix
Integral
proteins
Peripheral
protein
Cytosol
Fig. 5-6, p. 111

4. Membrane structure, II 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

5. (b) Fluid mosaic model. According to this model, a cell
Hydrophilic
region of protein
Hydrophobic
region of protein
Phospholipid
bilayer
Figure 5.2: Two models of membrane structure.
Integral
(transmembrane)
protein
Peripheral
protein
(b) Fluid mosaic model. According to this model, a cell
membrane is a fluid lipid bilayer with a constantly changing
“mosaic pattern“ of associated proteins.
Fig. 5-2b, p. 108

6. The Lipid Bilayer Lipids of the bilayer
fluid or liquid-crystalline state
Proteins move within the membrane

7. Membrane Proteins

8. Functions of Membrane Proteins

9. Membrane traffic
Diffusion~ tendency of any molecule to spread out into available space
Concentration gradient
Passive transport~ diffusion of a substance across a biological membrane without using energy
Osmosis~ the diffusion of water across a selectively permeable membrane

10. Diffusion

11. Osmosis

12. Pressure applied to piston to resist upward movement Water plus solute
Pure water
Selectively
permeable
membrane
Figure 5.12: Osmosis.
The U-tube contains pure water on the right and water plus a solute on the left, separated by a selectively permeable membrane. Water molecules cross the membrane in both directions (red arrows). Solute molecules cannot cross (green arrows). The fluid level would normally rise on the left and fall on the right because net movement of water would be to the left. However, the piston prevents the water from rising. The force that must be exerted by the piston to prevent the rise in fluid level is equal to the osmotic pressure of the solution.
Molecule
of solute
Water
molecule
Fig. 5-12, p. 117

13. Water balance 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

14. Osmotic Pressure

15. When a cell is placed in an isotonic solution, water
Outside
cell
Inside
cell
H20
molecules
Solute
molecules
No net water
movement
Figure 5.13: The responses of animal cells to osmotic pressure differences.
(a) Isotonic solution.
When a cell is placed in an
isotonic solution, water
molecules pass in and out
of the cell, but the net
movement of water
molecules is zero.
Fig. 5-13a, p. 118

16. (b) Hypertonic solution. When a cell is placed in a
Outside
cell
Inside
cell
Net water movement
out of the cell
Figure 5.13: The responses of animal cells to osmotic pressure differences.
(b) Hypertonic solution.
When a cell is placed in a
hypertonic solution, there
is a net movement of
water molecules out of the
cell (blue arrow). The cell
becomes dehydrated and
shrunken.
Fig. 5-13b, p. 118

17. (c) Hypotonic solution. When a cell is placed in a
Outside
cell
Inside
cell
Net water movement
into the cell
Figure 5.13: The responses of animal cells to osmotic pressure differences.
(c) Hypotonic solution.
When a cell is placed in a
hypotonic solution, the net
movement of water
molecules into the cell
(blue arrow) causes the cell
to swell or even burst.
10 μm
Fig. 5-13c, p. 118

18. Turgor and Plasmolysis

19. Plasma membrane Nucleus Vacuole Vacuole Vacuolar membrane (tonoplast)
Figure 5.14: Turgor pressure and plasmolysis.
Vacuolar
membrane
(tonoplast)
Plasma
membrane
Cytoplasm
Fig. 5-14, p. 119

20. 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

21. Facilitated Diffusion

22. Outside cell Glucose High concentration of glucose Low concentration
Figure 5.16: Facilitated diffusion of glucose molecules.
Glucose
transporter
(GLUT 1)
Cytosol 1
Glucose binds to GLUT 1.
Fig. 5-16a, p. 120

23. glucose is released inside cell.
Figure 5.16: Facilitated diffusion of glucose molecules. 2
GLUT 1 changes shape and
glucose is released inside cell.
Fig. 5-16b, p. 120

24. GLUT 1 returns to its original shape.
Figure 5.16: Facilitated diffusion of glucose molecules. 3
GLUT 1 returns to its original
shape.
Fig. 5-16c, p. 120

25. Types of Active Transport
Sodium-potassium pump
Exocytosis~ secretion of macromolecules by the fusion of vesicles with the plasma membrane
Endocytosis~ import of macromolecules by forming new vesicles with the plasma membrane •phagocytosis •pinocytosis •receptor-mediated endocytosis (ligands)

26. concentration gradient concentration gradient
Higher
Lower
Outside
cell
Active
transport
channel
concentration gradient
Potassium
concentration gradient
Sodium
Figure 5.17: A model for the pumping cycle of the sodium–potassium pump.
Lower
Cytosol
Higher
(a) The sodium–potassium pump is a carrier protein that requires
energy from ATP. In each complete pumping cycle, the energy of
one molecule of ATP is used to export three sodium ions (Na+)
and import two potassium ions (K+).
Fig. 5-17a, p. 121

27. causes carrier protein to change shape, releasing 3 Na+ outside cell.
2. Phosphate group is
transferred from ATP
to transport protein.
3. Phosphorylation
causes carrier protein
to change shape, releasing
3 Na+ outside cell.
1. Three Na+ bind
to transport protein.
4. Two K+ bind to
transport protein.
Figure 5.17: A model for the pumping cycle of the sodium–potassium pump.
6. Phosphate release causes
carrier protein to return
to its original shape. Two
K+ ions are released inside
cell.
5. Phosphate is released.
Fig. 5-17b, p. 121

28. Phagocytosis
Large particles enter cell

29. Receptor-Mediated Endocytosis

30. Intracellular junctions
PLANTS:
Plasmodesmata: cell wall perforations; water and solute passage in plants
ANIMALS:
Tight junctions~ fusion of neighboring cells; prevents leakage between cells
Desmosomes~ riveted, anchoring junction; strong sheets of cells
Gap junctions~ cytoplasmic channels; allows passage of materials or current between cells

31. Tight Junctions

32. Gap Junctions

33. Cell Signaling Synthesis, release, transport of signaling molecules
neurotransmitters, hormones, etc
ligand binds to a specific receptor
2. Reception of information by target cells

34. Cell Signaling 3. Signal transduction 4. Response by the cell
receptor converts extracellular signal into intracellular signal
causes change in the cell
4. Response by the cell

35. Cell Signaling

36. 1 Cell sends signal Signaling molecules Receptor 2 Reception Signaling
protein 3
Signal
transduction
Figure 6.2: Overview of cell signaling.
Protein
Enzyme
Protein that
regulates a gene 4
Response
Altered
membrane
permeability
Altered
metabolism
Altered
gene activity
Fig. 6-2, p. 136

37. Local Regulators Paracrine regulation Local regulators
diffuse through interstitial fluid
act on nearby cells
Local regulators
histamine
growth factors
prostaglandins
nitric oxide

38. Local Signals

39. Neurotransmitters
Chemical signals
released by neurons (nerve cells)

40. Hormones Chemical messengers Secreted by endocrine glands
in plants and animals
Secreted by endocrine glands
in animals
Transported by blood
to target cells

41. Hormones