2. Cell Physiology: Membrane Transport

3. Selective Permeability
Plasma membrane allows some materials to pass while excluding others

4. SOLUTION CONCENTRATIONS

5. I. Passive Transport Processes
Diffusion = Particles distribute evenly within a solution
Movement = high to low concentration
NO Energy required !
Figure 3.9

6. Simple diffusion: CAN pass through membrane !

7. b. Osmosis—water

8. 2. Facilitated diffusion
Require a protein carrier !
Lipid-insoluble & LARGE substances

9. 3. Filtration
Hydrostatic pressure  pressure gradient
Solute-containing fluid is pushed from high to lower pressure area

10. <BREAK>  LAB #6 – Part A: Transport Mechanisms

11. II. Active Transport Processes
Substances UNABLE to pass by diffusion
too LARGE !
HYROPHILIC --insoluble in lipid membrane
move AGAINST a concentration gradient
ATP is used for transport

12. 1. Solute pumping ex. “Na+ - K+ Pump”
Extracellular fluid K+ P
Na+ P
Cytoplasm K+
ADP
Loss of phosphate restores the original conformation of the pump protein. K+ is released to the cytoplasm and Na+ sites are ready to bind Na+ again; the cycle repeats.
The shape change expels Na+ to the outside. Extracellular K+ binds, causing release of the phosphate group.
Binding of cytoplasmic Na+ to the pump protein stimulates phosphorylation by ATP, which causes the pump protein to change its shape.

13. 2. Exocytosis
Moves materials OUT of the cell
Vesicle combines with plasma membrane

14. 3. Endocytosis
Extracellular substances are engulfed by being enclosed in a membranous vesicle

15. Endocytosis Exocytosis
Recycling of membrane and receptors (if present) to plasma membrane
Cytoplasm
Extracellular fluid
Plasma membrane
Detachment of vesicle
Vesicle containing ingested material
Vesicle
Vesicle fusing with lysosome for digestion
Release of contents to cytoplasm
Lysosome
Transport to plasma membrane and exocytosis of vesicle contents
Ingested substance
Pit
(a)
Figure 3.13a, step 6