Cell (plasma) membrane

Transcription

1 Cell Membranes & Movement Across Them Cell (plasma) membrane Cells need an inside & an outside separate cell from its environment cell membrane is the boundary IN food - s - proteins - s salts O 2 H 2 O OUT waste - ammonia - salts - CO 2 - H 2 O products - proteins cell needs materials in & products or waste out 1

2 Building a membrane How do you build a barrier that keeps the watery contents of the cell separate from the watery environment? What substance do you know that doesn t mix with water? FATS LIPIDS Remember: oil & water don t mix!! Membrane is made of special kind of lipid phospholipids split personality Membrane is a double layer phospholipid bilayer inside cell Lipids of cell membrane attracted to water phosphate lipid outside cell repelled by water 2

3 * UY 3

4 The Fluid Mosaic The Fluid- Mosaic Model * We have learned: * Proteins and substances such as cholesterol become embedded in the bilayer, giving the membrane the look of a mosaic. * Because the plasma membrane has the consistency of vegetable oil at body temperature, the proteins and other substances are able to move across it. * That s why the plasma membrane is described using the fluid- mosaic model. 4

5 The Fluid- Mosaic Model Semi-permeable membrane Cell membrane controls what gets in or out Need to allow some materials but not all to pass through the membrane semi-permeable only some material can get in or out So what needs to get across the membrane? lipids aa H 2 O salt waste O 2 5

6 Crossing the cell membrane What molecules can get through the cell membrane directly? s and oils can pass directly through inside cell lipid waste salt outside cell aa H 2 O but what about other stuff? How do you build a semi-permeable cell membrane? Channels are made of proteins proteins both like water & like lipids bi- lipid membrane protein channels in bi- lipid membrane 6

7 Cell membrane channels Need to make doors through the membrane protein channels allow substances in & out specific channels allow specific material in & out H 2 O channel, salt channel, channel, etc. inside cell H 2 O aa waste salt outside cell Protein channels Proteins act as doors in the membrane channels to move specific molecules through cell membrane HIGH LOW 7

8 Movement through the channel Why do molecules move through membrane if you give them HIGH? a channel?? LOW Molecules move from high to low Diffusion move from HIGH to LOW concentration 8

9 Move from HIGH to LOW concentration passive transport no energy needed Diffusion diffusion of water diffusion osmosis Simple Diffusion Move from HIGH to LOW inside cell LOW Which way will move? HIGH outside cell 9

10 Facilitated Diffusion Move from HIGH to LOW through a channel inside cell LOW Which way will move? HIGH outside cell Move from HIGH to LOW concentration directly through membrane simple diffusion no energy needed Diffusion help through a protein channel facilitated diffusion (with help) no energy needed HIGH LOW 10

11 Simple vs. facilitated diffusion simple diffusion facilitated diffusion inside cell lipid inside cell H 2 O protein channel outside cell outside cell H 2 O Transport summary simple diffusion facilitated diffusion active transport ATP 11

12 Active transport * Cells may need molecules to move against concentration hill * need to pump uphill * from LOW to HIGH using energy * protein pump * requires energy * ATP ATP 12

13 Transport summary simple diffusion facilitated diffusion active transport ATP POP QUIZ!!! * Please sit down it is time for a pop quiz. * Please take out a piece of paper * If you do not have one, raise your hand and I will hand you one * Please put up your wall on your desk 13

14 * I will not talk until it is silent * The class will receive a 0 if we do not start the quiz POP QUIZ * RULES: * You are allowed to use your notes * You are not allowed to use another student s notes * If you talk during the quiz, you will receive a zero * READY? 14

15 Here are the Questions * What molecules can cross the membrane through the process of simple diffusion? * Some molecules need help crossing the membrane, this help is given by what? * What are my 2 rules to follow? * Why is active transport different? (how does it break the rules?) Passage into and out of Cells * What if we want to get something large inside or out of the cell? * endocytosis is the engulfing of substances outside of the cell, forming a vesicle that brings the substances inside the cell * exocytosis is the discharge of substances from vesicles at the cell surface 15

16 Forms of Endocytosis * Phagocytosis is endocytosis of particulate (solid) matter * Pinocytosis is endocytosis of liquid matter * What organelle did we create? * Vesicles Exocytosis * What organelle would be used for this? * Vesicles 16

17 Receptor- mediated endocytosis * Transport of specific molecules into the cell involves receptor- mediated endocytosis * molecules to be transported must first bind to specific receptors in the plasma membrane Receptor- mediated endocytosis 17

18 Water + Food Coloring * With your tables discuss the following demonstration. * What is happening? * Why does this happen? * What is the process called? What have we learned? 18

19 Osmosis Movement of Water Across Cell Membrane Osmosis Water is very important, so we talk about water separately Osmosis diffusion of water from HIGH concentration of water to LOW concentration of water across a semi-permeable membrane 19

20 Keeping water balance Cell survival depends on balancing water uptake & water loss freshwater balanced saltwater 1 Keeping right amount of water in cell Freshwater a cell in fresh water high concentration of water around cell cell gains water example: Paramecium problem: cells gain water, swell & can burst water continually enters Paramecium cell solution: contractile vacuole pumps water out of cell KABOOM! No problem, here freshwater 20

21 2 Keeping right amount of water in cell I m shrinking, saltwater I m shrinking! Saltwater a cell in salt water low concentration of water around cell cell loses water example: shellfish problem: cell loses water in plants: plasmolysis in animals: shrinking cell solution: take up water I will survive! Controlling water Contractile vacuole in Paramecium 21

22 Controlling water * Contractile vacuole in Paramecium 22

23 Introduction of Hypertonic Solution 3 Keeping right amount of water in cell Balanced conditions no difference in concentration of water between cell & environment cell in equilibrium example: blood problem: none That s better! water flows across membrane equally, in both directions volume of cell doesn t change balanced I could be better 23