1. Chapter 10 Functions of Cell Membranes

2. Cell Membrane Functions 1.Selectively choose what’s inside or outside the cell…creating a concentration gradient 2.Regulate the exchange of substances 3.Communicate with other cells 4.Attach to other cells 5.Regulate biochemical reactions

3. Phospholipid Review Fatty Acid Glycerol Polar group Glycerol Fatty Acid Change from Triglyceride to Phospholipid

4. Phosphoplipids Phosphoplipids  are like triglycerides with one fatty acid  Phospholipids are abundant in biological membranes.  They self assemble into lipid bilayers  characteristic of the plasma membrane and organnelle membranes

5. 5 The plasma membrane  The plasma membrane is a bilayer of phospholipids that form a fluid matrix  various proteins are embedded in it.  Many proteins have carbohydrates attached to them, forming glycoproteins..

6. Membrane Proteins Form a Mosaic Proteins are embedded in the phospholipid bilayer Some proteins can float and drift Some proteins can float and drift Other proteins are anchored by protein filaments in the cytoplasm Other proteins are anchored by protein filaments in the cytoplasm Many proteins have attached carbohydrates ( glycoproteins ) Many proteins have attached carbohydrates ( glycoproteins )

7. Oligosaccharides CytoplasmCytoplasm Membrane Proteins Cholesterol Outer Surface Fluid Mosaic Model of Membrane Structure

8. Membrane Proteins Form a Mosaic Categories of membrane proteins Receptor Proteins Receptor Proteins Recognition Proteins Recognition Proteins Enzymatic Proteins Enzymatic Proteins Attachment Proteins Attachment Proteins Transport Proteins Transport Proteins

9. . The proteins serve several functions:  Transport proteins: Regulate the movement of water-soluble molecules through the plasma membrane.  Channel Proteins: Form pores that allow small molecules to pass.  Carrier Proteins: Have binding sites that bind specifically to specific proteins and move the molecules through the membrane.  Receptor Proteins: Trigger specific cellular responses when certain molecules bind to them.  Recognition Proteins: Serve as ID tags and cell- surface attachment sites.

11. Membrane Proteins Form a Mosaic Receptor Proteins Trigger cellular responses upon binding specific molecules, e.g. hormones Trigger cellular responses upon binding specific molecules, e.g. hormones Recognition Proteins( Marker Proteins) Serve as identification tags on the surface of a cell Serve as identification tags on the surface of a cell

13. Enzymes Promote chemical reactions that synthesize or break apart biological molecules Promote chemical reactions that synthesize or break apart biological molecules Attachment Proteins Anchor the cell membrane to inner cytoskeleton, to proteins outside the cell, and to other cells Anchor the cell membrane to inner cytoskeleton, to proteins outside the cell, and to other cells

14. Transport Proteins Include channel and carrier proteins Include channel and carrier proteins Regulate import/export of hydrophilic molecules Regulate import/export of hydrophilic molecules

15. Transport Processes How stuff gets across cell membrane. Passive transport Follows concentration gradient Follows concentration gradient Does not require energy Does not require energy Facilitated transport Follows concentration gradient Follows concentration gradient Requires gateway protein Requires gateway protein

16. Diffusion All molecules constantly vibrating Those in gas and liquid move randomly Mixtures tend to become uniform Move from high concentration to low Move from high concentration to low Concentration gradient Concentration gradient Doesn’t require energy Doesn’t require energy

17. Diffusion of Dye in Water Time 0 Steep Concentration Gradient Time 1 Reduced Concentration Gradient Dispersing Time 2 No Concentration Gradient Random Dispersal

18. Simple Diffusion (extracellular fluid) (cytoplasm) Some molecules diffuse freely across Some molecules diffuse freely across

19. Facilitated Diffusion: Carriers Carrier protein has binding site for molecule Molecule enters binding site Carrier protein changes shape, transporting molecule across membrane Carrier protein resumes original shape (Inside Cell) (Outside Cell) Diffusion Channel Protein Diffusion Channel Protein Diffusion Gradient Molecule in Transit Molecule in Transit

20. Osmosis Diffusion of water across membrane Special case of diffusion(Passive transport) Ex: Pure water on one side; sugar solution on other Ex: Pure water on one side; sugar solution on other Sugar molecules can’t cross, but crowd pores Sugar molecules can’t cross, but crowd pores Water crosses faster toward sugar Water crosses faster toward sugar Net water movement toward sugar Water follows concentration gradient

21. Osmotic Factors Compare cell’s environment with cell. If environment is: Hypotonic: Hypotonic: – “Hypo-” means environment “<” cell – Cell gains water Hypertonic: Hypertonic: – “Hyper-” means environment “>” cell – Cell loses water Isotonic: Isotonic: – “Iso-” means environment “=” cell – No change in cell volume

22. Osmosis “Bound” water molecules clustered around sugar: cannot fit through pore “Free” water molecule: can fit through pore

23. Normal RBCs Isotonic Solution The Effects of Osmosis Equal movement of water into and out of cells Net movement of water out of cells Net movement of water into cells Shriveled RBCs Swollen RBCs Hypertonic Solution Hypotonic Solution

24. Active Transport Requires energy Ex: Sodium/Potassium pump Energy from ATP One phosphate per “fare” Pumped by flip/flop changes in a membrane protein

25. Active Transport Steps Inside Cell Outside Cell Energy Provider Energy Provider Spent Energy Provider Spent Energy Provider Transported Molecule Transported Molecule 1234

26. Endo- & Exocytosis This is like cell eating & eliminating waste.Active processes for large groups of molecules. Endocytosis – Engulfment Endocytosis – Engulfment  Encloses particles in small portions of plasma membrane to form vesicles that then move into the cytoplasm.  Engulfment of surrounding fluid containing desired molecules. Exocytosis – Expulsion Exocytosis – Expulsion – Moves substances from cytoplasm to plasma membrane during secretion. – Expulsion of a group of waste products.

27. Endocytosis (extracellular fluid) Pinocytosis vesicle containing extracellular fluid) (cytoplasm) 1 2 3 cell (extracellular fluid) (cytoplasm) 1 2 3 4 coated pit forming Receptor-mediated Endocytosis Phagocytosis coated vesicle nutrients receptors food particle pseudopod particle enclosed in food vacuole

28. Receptor- mediated Endocytosis I Begins with a shallow pit in plasma membrane Pit is coated with protein (cytoplasm) (extracellular fluid) coated pit protein coating extracellular particles bound to receptors plasma membrane Pit deepens a a b b 0.1 Micrometer

29. Receptor- mediated Endocytosis II Pit deepens further and begins to pinch off Eventually becomes a coated vesicle d d c c 0.1 Micrometer coated vesicle

30. Exocytosis (cytoplasm) 1 Vesicle (extracellular fluid) plasma membrane 2 Secreted Material 3

31. Attributes of Cells Cell size 1–100 µm 1–100 µm Why is there a limit to cell size? Why is there a limit to cell size? – Surface-to-volume (S/V) ratio – Distance from surface to center

32. The End