1. Structure and Function
Membranes
Structure and Function

2. Membrane Structure Phospholipid Bi-layer
Contains Different Types of Proteins
Channel proteins
Protein Pumps proteins
Adhesion proteins
Cell-to-Cell Communication proteins
Hormone Receptor proteins
Immobilized Enzymes
Fluid Mosaic Model

3. Phospholipid Bi-layer
Contains
Glycoproteins
Integral Proteins
Peripheral Proteins
Cholesterol

4. Channel proteins Integral protein: embedded across bi-layer
Allows for movement of molecules across cell membrane

5. Protein Pumps Integral protein
Transports molecules across membranes by changing shape

6. Adhesion proteins
Connects internal cytoskeleton to external points of attachment
Secures cells of multi-cellular organisms in place

7. Cell-to-Cell Communication proteins
Cells within the same organism use membrane proteins to recognize each other
Often use glycoproteins
Major importance to immune system

8. Hormone Receptor proteins
Hormones bind to cell surface proteins
Initiates a series of reactions within cell
Results in cellular response such gene expression (making more or less of a protein)

9. Immobilized Enzymes
Many enzymes used by cells are embedded within membranes
Useful in keeping certain reactions in specific parts of the cell

12. Membrane Function Boundary Separates Two Environments
Selectively Permeable
Passive Transport
Simple Diffusion
Facilitated Diffusion
Active Transport
Protein Pumps
Endocytosis / Exocytosis

13. Selectively Permeable
Membranes and their proteins allow only certain molecules to cross
Diffusion: movement of a substance from an area of high concentration to low concentration
Osmosis: movement of water from an area of low solute concentration to high

14. Diffusion

15. Osmosis

16. Passive Transport
The movement of a molecule across a membrane from high to low concentration
Molecules move with the concentration gradient
Simple Diffusion
No proteins needed
Facilitated Diffusion
Membrane proteins required

17. Simple Diffusion
Small, uncharged molecules can move directly across membrane
Includes gases (CO2 and 02 ) and water

18. Facilitated Diffusion
Uses either protein channels or transporters (change shape)
Channel Transporter

19. Passive Transport

20. Active Transport
Movement of molecules across a membrane from low concentrations to high
Molecules move against the concentration gradient
Requires a protein transporter (pump) and energy supplied by ATP
Ex. sodium/potassium pump

21. Active Transport

22. Active Transport

23. Passive Vs. Active Transport

24. Endocytosis
Cell membrane surrounds and engulfs food particle or extra-cellular fluid
Results in vesicle inside cell
Phagocytosis: engulfing large particles like bacteria
Pinocytosis: engulfing extra-cellular fluid and whatever it might contain

27. Exocytosis Opposite of endocytosis
Vesicle containing secretory proteins or wastes joins with plasma membrane
Molecules inside vesicle are then released outside of the cell

29. Summary

30. Review Questions
Name 5 types of membrane proteins and describe their functions
What is the most significant difference between passive and active transport?
Why are transport proteins necessary in facilitated diffusion?
Why does active transport require energy?

31. Problems #1
The internal cell concentration of sucrose is 1M, the external concentration is .1M, how might a cell raise the internal concentration to 2M without using a metabolic pathway? #2
What might happen if a cell continually secreted enzymes, but never participated in endocytosis?