1. Lecture 3.0 – Membrane and Membrane Transport Genalin Lagman Taguiam Spring 2012-2013

2. Course Outcomes
On completion of the week’s activity, the students should be able to
describe the basic transport mechanisms of cell membrane (selective permeability, diffusion, osmosis, active transport, passive transport, exocytosis, endocytosis, phagocytosis);
define the terms hypertonic, hypotonic, isotonic.

3. Plasma Membrane encloses cell contents
mediates exchanges with the extracellular environment
plays a role in cellular communication
acts as a selectively permeable barrier

4. Plasma Membrane
substances move across the plasma membrane by passive processes, which depend on the kinetic energy of molecules or on pressure gradients, and by active processes, which depend on the use of cellular energy adenosine triphosphate (ATP)

5. Membrane Transport diffusion
movement of molecules (driven by kinetic energy) down a concentration gradient
Movement of electrolytes and other substances from an area of higher concentration to an area of lower concentration
fat-soluble solutes can diffuse directly through the membrane by dissolving in the lipid

6. Diffusion

8. Membrane Transport facilitated diffusion
passive movement of certain solutes across the membrane either by their binding with a membrane carrier protein or by their moving through a membrane channel
as with other diffusion processes, it is driven by kinetic energy, but the carriers and channels are selective

10. Diffusion

11. Membrane Transport osmosis
diffusion of a solvent, such as water, through a selectively permeable membrane
water diffuses through membrane pores (aquaporins) or directly through the lipid portion of the membrane from a solution of lesser osmolarity (measure of solute concentration) to a solution of greater osmolarity

12. net osmosis ceases when the solute concentration on both sides of the plasma membrane reaches equilibrium

13. Osmosis
the presence of solutes unable to permeate the plasma membrane leads to changes in cell tone that may cause the cell to swell or shrink

14. Osmosis
hypotonic
solutions that cause a net water gain of the cells

15. Osmosis
hypotonic
contain lesser amount of solutes than the serum of the blood

16. Osmosis
isotonic
solutions that cause neither gain nor loss of water from cells

17. Osmosis
isotonic
contain the same amount of solutes or electrolytes as the serum of the blood

18. Osmosis
hypertonic
solutions that cause a net loss of water from cells

19. Osmosis
hypertonic
contain more amount of solutes than the serum of the blood

20. Membrane Transport filtration
occurs when a filtrate is forced across a membrane by hydrostatic pressure
non selective and limited only by pore size
the pressure gradient is the driving force

21. Membrane Transport active transport “solute pumping”
depends on a carrier protein and ATP
substances transported move against concentration or electrical gradients
Amino acids, some sugars, and most ions are transported by solute pumps
Energy is required to pump ions against their concentration gradient or against an electrical or chemical gradient

23. Membrane Transport vesicular transport also requires ATP ¹exocytosis
anchors the vesicles to the plasma membrane, ejects substances (hormones, wastes, secretions) from the cell
²endocytosis
brings substances into the cell in protein-coated vesicles
if the substance is particulate, the process is called phagocytosis
if the substance is dissolved molecules, the process is pinocytosis

27. References
Marieb, E.N. (2010). Human anatomy and physiology (8th Ed.). San Francisco, Pearson.
Marieb, E.N. (2006). Human anatomy and physiology (7th Ed.). San Francisco, Pearson.
Tortora, G. J. (2006). Principles of anatomy and physiology. (11th. Ed.). New Jersey, John Wiley and Sons, Inc.