1. Cell Membranes and Cell Transport Lecture

2. Cell Diversity

3. General Structure of Cells

4. Cell Membrane Protects the Cell

5. Cell Membrane Structure

6. Phospholipid Bilayer

7. Proteins in Cell Membrane
These are the “windows” and “doors” of the cell.

8. Cell Membrane Controls What Enters/Leaves the Cell
The small, curved arrows indicate that these structures cannot cross the plasma membrane, and the large arrows indicate that these substances can cross the plasma membrane.

9. Membrane Proteins Form Channels

10. Membrane Proteins Act as Receptors

11. Membrane Proteins Connect Cells Together

12. Membrane Proteins Allow Cells to Communicate

13. Cholesterol in Cell Membrane

14. Glycoproteins and Glycolipids in Cell Membrane

15. Cell membranes allow materials to enter or leave the cell
Membrane Transport
Cell membranes allow materials to enter or leave the cell

16. Diffusion
Random movement leads to net movement down a concentration gradient
Lump
of sugar
Water
No net movement at equilibrium

17. Diffusion
Diffusion Animation

18. Diffusion

19. Diffusion of water across a cell membrane
Osmosis:
Diffusion of water across a cell membrane
Osmosis Animation

20. Human Red Blood Cells Hyperosmotic solution Isosmotic solution
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Human Red Blood Cells
Cells swell and
eventually burst
Shriveled cells
Normal cells
Hyperosmotic
solution
Isosmotic
solution
Hypoosmotic
solution

21. Facilitated Diffusion
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Facilitated Diffusion _ _ -
Outside
Plasma
membrane
Inside
Transport Protein

22. Facilitated Diffusion
Facilitated Diffusion Animation

23. A Channel Protein H+ H+

24. Carrier Protein

25. Facilitated Diffusion with a Carrier Protein
Outside of cell
Inside of cell
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

26. Active transport
Active transport allows a solute (ion or molecule) to cross the membrane against its concentration gradient – from lower solute concentration to higher solute concentration. At (1), the molecule enters the carrier. During (2), the breakdown of ATP induces a change in shape that drives the molecule across the membrane. At (3), the carrier protein returns to its former shape or state.

27. Active Transport
Sodium Potassium Pump Animation

28. Endoctytosis
Phagocytosis
Pinocytosis
Receptor-Mediated Endocytosis

29. The substance engulfed is a solid particle
Phagocytosis
The substance engulfed is a solid particle
Phagocytosis occurs when the substance to be transported into the cell is large; amoebas ingest food by phagocytosis. Certain types of human white blood cells are amoeboid and engulf worn-out cellular debris or bacteria using phagocytosis. When an endocytic vesicle fuses with a lysosome, digestion of the vesicle contents occurs.

30. Process of Phagocytosis
Substance engulfed is a solid particle

31. Pinocytosis The substance engulfed is a liquid
Pinocytosis occurs when a macromolecule, such as a polypeptide, is to be transported into the cell. The resulting vesicle or vacuole is small. Pinocytosis occurs continuously, but the loss of plasma membrane due to vesicle formation is offset by exocytosis.

32. Receptor-Mediated Endocytosis
Particles join to specific receptors on the membrane causing it to indent, engulfing the particles in a vesicle
Receptor-mediated endocytosis is a form of pinocytosis. The substance to be taken in binds with a specific receptor protein, which migrates to a pit or is already in a coated pit. The resulting vesicle contains the substance and the receptor. Receptor-mediated endocytosis is responsible for cells taking uplow-density lipoprotein (LDL) when LDL receptors gather in a coated pit. In individuals with a genetic disorder called familial hypercholesterolemia, the LDL receptor is unable to properly bind to the coated pit, and cells are unable to take up cholesterol. Cholesterol accumulates in the walls of arterial blood vessels, causing severe health problems.

33. Transport of Cholesterol Receptor Mediated Endocytosis
Phospholipid outer layer
LDL particle
Vesicle
Cholesterol
Protein
Plasma
membrane
Receptor
protein
Cytoplasm

34. Exocytosis The reverse of endocytosis
During this process, the membrane of a vesicle fuses with the plasma membrane and its contents are released outside the cell:

35. Exocytosis