1. 1.3 & 1.4 Membrane Structure and Membrane Transport

2. Phospholipids PHOSPHOLIPIDS: are the foundations of the cell membrane.
The are amphipathic (are both hydrophilic and hydrophobic)
Hydrophilic: polar, water loving head
Hydrophobic: nonpolar, water fearing tails, made of 2 fatty acid chains

5. Lipid Bilayer
The phospholipids form a lipid bilayer (2 layers of phospholipids, with the adjacent hydrophobic tails)
This prevents the tail from having contact with “water” environments

6. Fluid Mosaic Model of The Cell Membrane
The cell membrane is fluid (ie not rigid)
Thus, it can change shape
Cholesterol molecules in the bilayer allow for this fluidity
(At moderate temperatures, cholesterol makes the bilayer less fluid. At colder temperatures, it makes it slightly more liquid. This helps maintain functionality and strength of the membrane over a wide range of temperatures)

7. The fluid mosaic model proposes that proteins float in the fluid lipid bilayer (like boats on a pond)
Some are anchored and cannot move
These tend to be Integral Proteins, which span the bilayer
Some can float freely and can move within the membrane
These tend to be Peripheral or Surface Proteins, which are found only on one side of the bilayer

8. Proteins found in the Plasma Membrane

9. Transport Protein
These are protein pores which allow ions and molecules to pass into or out of the cell.
They can be:
Protein Channels (which do not require energy to transport material)
Protein Pumps (require energy to transport material)

10. Enzymes Biological Catalysts (speed up chemicals reactions)
Membranes provide a convenient surface for enzymes to be embedded.
Enzymes for related reactions are organized next to each other in order to organize the reactions for greater efficiency.

11. Cell Surface Receptors
Many proteins have a “lock and key” surface to which only specific substances can fit.
When the appropriate substance binds to the proteins, it may initiate a reaction in the cell or cause the substance to be brought into the cell (receptor mediated transport)
This is how some large food molecules, chemical messengers, or even viruses enter cells

12. Cell Surface Identity Markers
Each cell carries its own ID markers (glycoproteins – proteins with carbohydrate molecules attached to them)
These molecules identify the cell as belonging to that individual organism

13. Cell Adhesion Proteins
Allow adjacent cells to stick together via interlocking proteins on their membranes

15. Membrane Permeability
Permeable: all molecules can pass though (ie: pores in the membrane)
Non-permeable: nothing can pass through (ie: no pores in the membrane)
Semi-permeable: allows only small molecules to pass through (because there are small pores in the membrane)
The cell membrane is semi-permeable

16. Cell Transport How do molecules move through the cell membrane?
PASSIVE TRANSPORT
Movement of molecules from high to low concentration
Does not require energy
ACTIVE TRANSPORT
Movement of molecules from low to high concentration
Requires energy (ATP energy)

17. Passive Transport Diffusion
Random movement of any molecule from high to low concentration (with the concentration gradient)

18. Animations

19. Passive Transport 2. Osmosis Diffusion of water across a membrane
Water moves from high concentrations of water to low concentrations of water OR
Water move from low solute concentration to high solute concentration

20. Osmosis

21. Terms Associated with Osmosis
ISOTONIC
(iso = equal / tonic = solute)
2 solutions (inside and outside the cell) with equal concentrations of solute and water.
Net flow of water between the 2 is equal.
We say both are in equilibrium.
H2O diffusion still occurs in both directions at equilibrium

22. Cells want to reach equilibrium (have an equal concentration of solutes inside and outside the cell)
If the concentration of solutes is too high inside the cell or too low, the cell will either take in or release water

23. Terms Associated with Osmosis
HYPERTONIC
(hyper = more / tonic = solute)
Any solution having more solute (less H2O) than inside cell.
Water will flow out of cell so cell shrinks.
Ex: If a cell was put into a salt water solution, water would move out of the cell to “dilute” the extracellular fluid

24. Terms Associated with Osmosis
HYPOTONIC
(hypo = less / tonic = solute)
Any solution having less solute (more H2O) than the cell contents.
Water moves into the cell (which has more solute, less H2O) so cell expands.
(Think of a hippopotamus with bloated cheeks)

25. Animations

26. Passive Transport 3. Facilitated Diffusion
Passage of molecules from high to low concentration (diffusion) through a protein channel
The protein channels are unique in size and shape and only allow particular molecules to move through them.
Used when the molecules are too large to diffuse directly through the phospholipid bilayer or do not have the proper charge

28. ACTIVE TRANSPORT
Movement of materials AGAINST the concentration gradient (from low to high concentration)
Requires ATP enery
1. Endocytosis
Movement of molecules INTO the cell

29. Types of Endocytosis Phagocytosis
Movement of large particles into the cell by the formation of vacuoles
Cell “eating”
This is how some unicellular organisms (ie amoeba) eat
Involves the formation of pseudopods (false feet)
Usually receptor mediated endocytosis (the molecule entering the cell activates endocytosis by binding to receptors)

31. Types of Endocytosis b) Pinocytosis Cell “drinking”
The movement of liquid material or small particles into the cell by vacuole formation

32. Active Transport 2. Exocytosis Movement of materials out of the cell
Vacuole passes plasma membrane to dump contents out of the cell

35. Active Transport 3. Protein Pump
Transport protein that moves materials in or out of the cell (against the concentration gradient) but requires energy (ATP) to be activated
Ex: Sodium-Potassium Pump
Moves 3 Na+ out of the cell and 2 K+ into the cell

36. http://highered. mcgraw-hill

37. Homework
Read about the Davson-Danielli Model (of the membrane) pages 26-28