1. 2.4 Cell Membranes and Transport
Phospholipids: foundation of cell membrane
Hydrophilic: polar, water loving head made of phospholipid.
Hydrophobic: nonpolar, water fearing tails made of 2 fatty acid chains

3. The cholesterol makes the phospholipid bilayer less fluid at moderate temperatures, but slightly more liquid than it normally would be at cold temperatures. This helps maintain its functionality and strength over a wide range of temperatures.

4. Fluid Mosaic Model of Cell Membranes
Proposes that proteins float in the fluid lipid bilayer (like boats on a pond)
It states that proteins float in the lipid bilayer, some anchored, others floating freely. Occasional cholesterol molecules add extra fluidity. Because it is fluid, the membrane's shape may be altered.

5. Proteins Found within the Plasma Membrane

6. The plasma membranes of eukaryotic cells are made of bilayer lipid molecules. Suspended within this double layer of phospholipid molecules are numerous proteins, which play varied roles in relation to the membrane. These proteins float within the phospholipids and can move about, just like the phospholipids can move!

7. Examples of Proteins in the Plasma Membrane Include:
1. Transport Channel Proteins (D):
Proteins pores (w/ 'lock & key gate') through which ions and macromolecules may pass.
2. Enzymes (I):
Membranes provide a convenient surface for enzymes to be embedded. Enzymes for related reactions are organized next to each other, organizing the reactions for greater efficiency.
(ex. Electron transport chain)

8. 3. Cell Surface Receptors (B):
Many proteins have 'lock & key' surfaces, which will only fit to specific substances. When the chemical binds to the protein, it is brought into the cell (via facilitated diffusion). This is how some large food macromolecules, chemical messengers, or even viruses enter cells.

9. 4. Cell Surface Identity Markers (E):
Each cell carries its own ID markers (glycoproteins- proteins with carbohydrate markers) which identify the cell as belonging to that individual organism.
5. Cell Adhesion Proteins (A):
Adjacent cells stick together via interlocking proteins on their membranes.

10. permeable- holes in membrane are large & all molecules pass through.
Membrane permeability (ability to allow chemicals to pass / not pass across it):
permeable- holes in membrane are large & all molecules pass through.
semi-permeable- smaller holes in membrane allow only small molecules to pass through.
non-permeable - no holes in membrane. Nothing passes through.

11. Examples of Cell Transport
Passive Transport - Movement of molecules from high to low concentration. Needs no energy input.
Active Transport - Movement of molecules from low to high concentration (opposite the flow of diffusion). Needs input of energy (ATP).

12. Concentration

13. Examples of Passive Transport:
1. Diffusion: Random movement of any molecules from higher to lower concentration.
Animation:
[Diffusion / Osmosis #1]
2. Osmosis: Diffusion of water across a membrane. Occurs from high concentration of H2O to low conc. H2O, (or low solute conc. to high solute conc.).

14. Terms Associated with Osmosis in Cells:
Hypertonic: (hyper = more / tonic = solute)
a) Any solution having more solute (less H2O) than inside cell. More water flows out of cell so cell shrinks.

15. Terms Associated with Osmosis in Cells:
Hypotonic: (hypo = less / tonic = solute)
a) Any solution having less solute (more H2O) than the cell contents. Water diffuses into the cell (which has more solute, less H2O) so cell expands.

16. Terms Associated with Osmosis in Cells:
Isotonic: (iso = equal / tonic = solute)
2 solutions 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

19. 3. Facilitated Diffusion: passive transport (no energy required).
Passage of molecules from high to low concentration (diffusion) across membrane via binding to a membrane protein which carries it across.
Animation: [Facillitated Diffusion]
4. Ion channels: Special channel proteins allow ions to pass through membrane w/out interacting with hydrophobic lipid tails.

20. Cell Transport, Part II
Active Transport: requires large amounts of energy (ATP) to 'pump' materials against force of diffusion (low to high).
A. Endocytosis (bulk passage): move large polar molecules. This action requires energy input (ATP) by cell.
Animation: [Receptor-mediated Endocytosis]

21. Types of Endocytosis:
1) Phagocytosis: cell eating of large particles by formation of vacuoles.

22. 2) Pinocytosis: cell drinking, liquid material brought into cell by vacuole formation.
Animations: [Pinocytosis] [Pinocytosis]

23. B. Exocytosis: materials discharged from cell (vacuole passes plasma membrane to dump contents out of cell).

24. C. Sodium-potassium pump. Moves 3 Na + out of cell & 2 K+ into cell
C. Sodium-potassium pump. Moves 3 Na + out of cell & 2 K+ into cell. Both Na+ and K+ are moved from low to high concentration.

25. Sodium Potassium action potential video