Lecture 1 Outline (Ch. 7)

2. Lecture 1 Outline (Ch. 7) • Plasma Membrane • A. bilayer • B. fluidity • C. proteins • II. Transport across membranes • Simple diffusion • Osmosis & Facilitated diffusion • Active transport • Bulk transport • III. Preparation for next lecture

3. Membrane structure

4. Membrane structure

5. Membrane structure Experiment to determine membrane fluidity: • marked membrane proteins mixed in hybrid cell

6. Membrane structure • cell can alter fatty acid tail saturation  affects fluidity • cholesterol keeps membrane fluid at different temperatures

7. Membrane structure 1915, knew membrane made of lipids and proteins Where to place proteins? Lipid layer 1 Proteins Lipid layer 2

8. Membrane structure • freeze fracture • proteins intact, one layer or other • two layers look different

9. Membrane structure • cell membrane – amphipathic - hydrophilic & hydrophobic hydrophilic hydrophobic hydrophilic • membrane proteins that are inserted, also amphipathic

10. Membrane structure “fluid mosaic model” – 1970s • fluid – phospholipids move around Glycoproteins Integral Glycolipids Peripheral • mosaic – proteins embedded in membrane

11. Based on what we just discussed, of the following choices, which is true of cell membranes? • Membranes are hydrophobic inside the cell • Phospholipid tails are hydrophilic • Membrane proteins are amphipathic • Fluidity is static (not able to change) • Proteins are sandwiched between the two lipid layers

12. Membrane Proteins

13. Membrane Proteins Remember secondary and tertiary protein structure?!

14. Membrane Proteins Hydrophobicity plot: determine hydrophobic/hydrophilic for each region of a protein

15. Membrane Proteins What would a hydrophobicity plot look like for this protein?

16. Transport Across Membranes • Types of transport: • Passive transport • 1. simple diffusion • 2. osmosis & other facilitated diffusion • B. Active transport • C. Bulk transport Keep track: • Is Energy Required? • Direction of Movement?

17. Selectively Permeable Membranes • Small, non-polar molecules can move by simple diffusion

18. Selectively Permeable Membranes • Large or charged molecules need help crossing membrane

19. Facilitated Diffusion - Large, charged, polar (sugar, ions, water) • NO ENERGY required • DOWN concentration gradient • Use transport proteins - channel or carrier proteins

20. Passive Transport - Osmosis • osmosis – movement of water across cell membrane • osmosis is a type of diffusion • water moves via special channels called aquaporins • water moves into/out of cell until soluteconcentration is balanced

21. animal cell plant cell Passive Transport - Osmosis • tonicity – # solutes in solution in relation to cell - hypotonic – fewer solutes in solution - isotonic – equal solutes in solution - hypertonic – more solutes in solution

22. Passive Transport - Osmosis In each situation below, does water have net movement, and which direction: fewer solutes in solution, than in cell Isotonic? Hypertonic? Hypotonic? equal solutes in solution as in cell more solutes in solution, than in cell

23. Passive Transport - Osmosis Paramecium example • regulate water balance • pond water hypotonic • water into contractile vacuole – water expelled

24. Passive Transport - Osmosis Scenario: in movie theater, long movie. You are: drinking water What happens to your blood? • becomes hypotonic to cells • kidneys – remove water • body excretes water You are: eating popcorn What happens to your blood? • becomes hypertonic to cells • kidneys – uptake water • body retains water

25. Facilitated diffusion….. A. Requires energy and is up the conc. gradient B. Requires energy and is down the conc. gradient C. Does not require energy and is up the conc. gradient D. Does not require energy and is down the conc. gradient

26. Active Transport • ENERGY IS required - Usually ions or large molecules (Na+, K+, glucose) • UP/AGAINST concentration gradient • uses transport carrier proteins/pumps

27. Active Transport - Usually ions or large molecules (H+, Na+, K+, glucose) • ENERGY IS required • UP/AGAINST concentration gradient • Ex. proton (H+) pump • Pump H+ across inner membrane! • ATP used, pump H+ ions • uses transport carrier proteins/pumps *gradients – used by cell for energy potential

28. Bulk Transport – all types require energy! Exocytosis

29. Bulk Transport • Molecules moved IN  endocytosis • phagocytosis – “food” in • pinocytosis – water in • Molecules moved OUT - exocytosis

30. Self-Check

31. Things To Do After Lecture 1… • Reading and Preparation: • Make sure you are ready for lab 1 this week • Re-read today’s lecture, highlight all vocabulary you do not understand, and look up terms. • Read chapter 7, focus on material covered in lecture (terms, concepts, and figures!) • Ch. 7 Test Your Understanding: #1-4, 6 (correct answers in back of book) • Skim next lecture (ch. 8) • “HOMEWORK” (NOT COLLECTED – but things to think about for studying): • Draw and label a phospholipid bilayer including integral and peripheral proteins. • Name three molecules that easily cross membranes; name three molecules that are blocked by cell membranes. • Describe diffusion and osmosis – then, how is active transport different?