1. Today: Membrane Function Structure & Function
Biology Homework due Monday; Lab 5 on Monday!

2. The Fluid Mosaic Model

3. Origins of Membrane Proteins
Result:
Membranes have an “inside” and an “outside”

4. Types of Membrane Proteins
Most common:
Integral proteins penetrate the hydrophobic core and may also be…
Transmembrane proteins completely span the membrane
Peripheral proteins aren’t embedded in the membrane at all

5. Role of Carbohydrates On the Cell Membrane
Typically branched oligosaccharides bonded to lipids (=glycolipid) or proteins (=glycoproteins)

6. Functions of Membrane Proteins:

7. What types of things does a cell need to get across its membrane?
Brainstorm
What types of things does a cell need to get across its membrane?
Of those things, which can cross freely?? Why?? What about everything else??

8. X Cell membranes are SELECTIVELY PERMEABLE
O2, CO2, and other small, nonpolar molecules;and H2O
large, polar molecules; ions
such as H+, Na+, CI-, Ca++; X

9. Transport Proteins
Transport proteins provide a hydrophillic channel (doorway?) through the membrane
Transport proteins may also bind to molecules or ions and move them across the membrane

10. Passive transport is diffusion across a membrane
Substances diffuse down their concentration gradients in a spontaneous process

12. Passive Transport of Water = Osmosis
The direction of osmosis is determined by the total solute concentration, or tonicity
Solutions may be hypertonic, hypotonic, or isotonic to each other.

13. What will happen if I separate these two solutions with a selectively permeable membrane???

15. Osmosis in Cells Without Walls
Organisms with cells without walls have adaptations for osmoregulation
Possible mechanisms??

16. POP QUIZ!
Normal Red Blood Cells
Shriveled Red Blood Cells

17. Net Movement of Water in Isotonic, Hypotonic, and Hypertonic Solutions

18. Osmosis in Cells with Walls
Osmosis helps a plant cell maintain turgor pressure in a hypotonic environment
When cells lose their turgor pressure, they become flaccid as the membrane pulls away from the cell wall (plasmolysis)

19. Facilitated Diffusion
Passive diffusion aided by a transport protein
(ex. Aquaporins)
Gated Channel
Channel Protein

20. Active Transport
What happens to the charge inside and outside the cell when this pump runs?

21. Membrane Potential
All cells have voltage (separation of charges) across their membranes
Cytoplasm is negative (-50 to -200 millivolts)
Thus molecules can be driven across membrane by both a chemical force (concentration gradient) and an electrical force. This combination = electrochemical gradient

22. Transport proteins that generate voltage are called electrogenic pumps
Membrane Potential
Transport proteins that generate voltage are called electrogenic pumps

23. Review:

24. Active Transport: Cotransport
An ATP-powered pump can indirectly drive the transport of other molecules

25. EXOCYTOSIS OF A VESSICLE
TRANSPORT PROTEINS work well for individual molecules, but…
LARGE ITEMS (or molecules) must be transported by EXOCYTOSIS or ENDOCTOSIS
PLASMA MEMBRANE
EXOCYTOSIS OF A VESSICLE

26. ENDOCYTOSIS
PLASMA MEMBRANE

27. Three Types of Endocytosis
Phagocytosis (“cellular eating”)
Pinocytosis (“cellular drinking”)
Receptor-mediated endocytosis