1. Part III: Cellular Processes
The Structure of the Cell Membrane and processes that move materials across the membrane

2. A. The Structure of the Cell Membrane
The Fluid Mosaic Model
Not rigid, fluid-like with movement of molecules.
Proteins drift from place to place among the phospholipids.
Semi-permeable (selectively Permeable) = a barrier that allows only certain substances to pass through

3. 2. Structure of the Cell Membrane

4. Animation of the Structure of the Cell Membrane
YouTube - Active transport

5. Letter a = Phospholipid Bilayer
= 1 phospholipid; 2 layers to create the main portion of the membrane.
Lipids: Form a barrier to most substances because most substances can not dissolve through lipid.

6. Primary Component of the cell membrane
Small molecules (water, carbon dioxide, oxygen) can pass directly between the heads of the phospholipids which do not fit tightly together. The membrane is permeable to these materials.

7. Letter b = Transport Proteins (AKA Channel Proteins or Carrier Proteins)
*Protein molecules embedded through entire phospholipid bilayer.
*Aid in the movement of molecules into and out of the cell.

8. Letter c = Receptor Proteins (AKA) Surface Proteins
* Help the cell to receive chemical information
* Allow substances to bind to the surface of the cell.
*Some act as enzymes to mediate chemical reactions

9. Letter d = Recognition Proteins (AKA) Glycoproteins with Carbohydrate Branches
*Help to identify cell type (mammal, human, liver, lung, etc.)
*Help with cell adhesion = cells stick together to form tissues

10. B. Processes that Move Materials Through the Cell Membrane
*Two categories of process =
Passive processes VS
Active Processes

11. 1. Passive Transport Does not require energy expenditure by the cell.
A concentration gradient must exist = a difference in the amount of a molecule in a given space (High vs Low)
Movement of molecules is from high concentration to low concentration
Movement continues until EQUILIBRIUM is reached = balanced amount of molecules throughout the space.

12. DIFFUSION
A type of passive transport

13. DIFFUSION =
*The movement of molecules of a solution from an area of high concentration to an area of low concentration until equilibrium is reached.

15. Two substances that move across the membrane by diffusion are oxygen (O2) and carbon dioxide (CO2)
capillary
Blood from lungs
muscle cell
Blood coming from lungs has a higher concentration of O2 than the cell.
O2 diffuses from the blood into the cell
Cell has higher concentration of CO2 than the blood
CO2 diffuses from the cell to the blood

16. b. OSMOSIS
The diffusion of WATER across a semi-permeable membrane (like the cell membrane).
*Dependent on the amount of solute in a solution where the solvent is water.

17. Solute = dissolved substances
Let’s Review: Properties of Solutions
NOT ON NOTE SHEET!
All solutions consist of a solvent and solutes.
Solvent = the liquid
In cells this would be water.
Solute = dissolved substances
In cells this would be substances like protein, carbohydrate, lipid, salt, minerals, vitamins, etc.

18. Cells are surrounded by tissue fluid
which fills up the spaces between them.
Cell membrane
Tissue fluid ( a solution!)
H2O
Cytoplasm ( a solution!)
H2O
Water can move from the surrounding solution into the
cell,
or from the cell into the surrounding solution.
The direction of water movement depends on the concentration
of water molecules on either side of the cell membrane

19. If the water concentration is the same in the cell and the surrounding fluid, water will move into and out of the cell at the same rate.
H2O
70%
H2O
30% solutes
70% H2O
H2O
H2O
H2O
H2O
The cell will STAY THE SAME SIZE
H2O
The surrounding solution is ISOTONIC with respect to the cell.

20. If water molecules are more highly concentrated inside the cell than in the surrounding solution, water will move out of the cell
70% H2O
30% solutes
50% H2O
50% solutes
The cell will SHRINK
H2O
H2O
The surrounding solution is HYPERTONIC with respect to the cell.
H2O
H2O
H2O

21. If water molecules are more highly concentrated in the surrounding solution than they are in the cell, water will move into the cell
70% H2O
30% solutes
90% H2O
10% solutes
The cell will SWELL
H2O
H2O
H2O
H2O
H2O
The surrounding solution is HYPOTONIC with respect to the cell.

22. Elodea cells in an isotonic solution
Elodea cells in an hypertonic solution

23. Human red blood cells in an isotonic solution
hypotonic
Human red blood cells in an isotonic solution
Human red blood cells in a hypotonic solution

24. A B C
Can you identify the type of solution surrounding each cell?

25. c. Facilitated Diffusion =
The diffusion of a large molecule that is aided by a transport protein.
Movement of the molecules is always from high concentration to low concentration

26. 1
Blood (outside cell)
EXAMPLE: Glucose 2
Cell membrane
Cytoplasm of cell 3
Frame #1 = After a meal, glucose is highly concentrated in the blood, and in low concentration in the cells.
Frame #2 = Carrier protein specific for glucose, accepts glucose molecule.
Frame #3 = Carrier protein helps glucose molecule to move into the cell.

27. 2.ACTIVE Transport
A cell must expend ATP energy to move molecules across the membrane.
*The movement of molecules is from low concentration to high concentration (against the concentration gradient).

28. a. Endocytosis Active transport of molecules INTO the cell.
Can involve a transport protein or the cell membrane engulfing molecules.

29. EXAMPLE #1: Transport of Amino Acids into the cell after the digestion of a protein.

30. View 1 = The cell requires amino acids to assemble proteins.
There is a higher concentration of amino acids inside the cell than outside the cell
A transport protein opens

31. View 3 = Active transport of an amino acid is complete.
View 2 = An amino acids is moved against the concentration gradient into the cell.
* Energy is used by the cell.
ATP
View 3 = Active transport of an amino acid is complete.

32. 1. Phagocytosis A specific type of endocytosis
Occurs when the cell membrane engulfs solid particles to carry them into the cytoplasm.
Nickname = “Cellular Eating”

33. Example: A White Blood Cell (Macrophage = a type of phagocyte) engulfing Bacteria.
View 1 = Bacteria (H) in the blood are approached by a white blood cell. The membrane begins to fold inward.

34. View 2 = The membrane continues to fold inward and surrounds the bacteria.
View 3 = The membrane pinches off around the bacteria. This creates a vacuole in the cytoplasm that will eventually fuse with a lysosome in order to destroy the bacteria.

35. Animation of Phagocytosis
YouTube - The Process Of Phagocytosis

36. Example: An Amoeba feeding

37. Animation of an amoeba using phagocytosis to eat.
YouTube - Amoeba Feeds!

38. 2. Pinocytosis A specific type of endocytosis
Occurs when the cell membrane engulfs liquids to carry them into the cytoplasm.
Nickname = “Cellular Drinking”

39. Pinocytosis

40. b. EXOCYTOSIS Active transport of molecules OUT OF the cell.
Can involve a transport protein or vacuole can push materials out through the cell membrane.

42. Passive Transport: REVIEW: *Diffusion *Osmosis *Facilitated Diffusion
NO USED BY THE CELL!
ATP

43. Active Transport: *Endocytosis *Exocytosis USED BY THE CELL!
- Phagocytosis
- Pinocytosis
*Exocytosis
ATP
USED BY THE CELL!