8.2 Transport Across Cell Membranes

1. 8.2 Transport Across Cell Membranes

2. Terms… • Selective Transport: the movement of only certain substances across the cell membrane • Particle Model of Matter – all matter is made of tiny particles • Brownian motion – in a liquid or a gas, particles are in constant, random motion • Brownian motion video: • http://www.youtube.com/watch?v=2Vdjin734gE

3. Terms… • Concentration Gradient – the difference in concentration between two areas for any given molecule produces a gradient or path of movement in which molecules move toward areas where the concentration of particles is lower. • Molecules move down a concentration gradient • Equilibrium – a state at which molecules are evenly distributed (the concentration is equal throughout the medium) • Molecules continue moving but equilibrium is maintained

4. Types of Transport Across Membranes • Passive Transport – movement across cell membranes without an input of energy Q. Name 2 reasons molecules move 1. Brownian Motion 2. Concentration gradients

5. Three Types of Passive Transport • Diffusion – the net movement of particles from an area of high concentration to an area or low concentration (down the gradient) - no energy is expended - In a cell, very small particles can cross the cell membrane by moving between the phospholipid molecules http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html • Match demo • Handout, do first diagram

6. Diffusion • Q: Why does oxygen diffusion into the cell never reach equilibrium? • A: your cells continually consume oxygen for cellular respiration, making the concentration inside always lower than the outside • Q: describe the concentration gradient of carbon dioxide. • A: higher concentrations in the cell so net movement is out of the cell

7. Passive Transport: 2. Osmosis Osmosis: the diffusion of water molecules across a membrane (water molecules move from where they are more highly concentrated to where they are less concentrated; down their concentration gradient) Water molecules will go to the side that more solute is on. Solutions are described in terms of their concentration relative to another solution. http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

8. Osmosis • Hypotonic solution – has a lower concentration of solute compared to outside the cell • Water is therefore more concentrated insidethe cell and water will leave the cell (cell shrinks). • Hypertonic solution – has a higher concentration of solute compared to the outside of the cell • Water is therefore less concentrated insidethe cell and water will enter the cell (cell swells)

9. Osmosis c) Isotonic solution – has the same solute concentration on both sides of the cell membrane. Equilibrium has been reached.

10. Q: What happens when a cell is placed into distilled water? A:The cell is hypertonic and water moves into the cell & the cell may burst

11. Osmosis Q: what is turgor pressure? A:the cell wall of a plant resists the pressure of a water-filled vacuole keeping the plant firm. Q: What happens when a cell is placed into a strong salt water? A: the solution is hypertonic and water leaves the cell. The cell shrinks and may die (plasmolysis) Q: What is plasmolysis? A:loss of water in a plant cell resulting in wilting (cell shrinks) Q: Why would drinking saltwater pose a problem? A: Hypertonic solution outside cells would cause cells to lose water, shrink and die (dehydration)

12. Passive Transport: 3. Facilitated Diffusion Facilitated Diffusion: diffusion of molecules across the cell membrane by way of transport proteins. - necessary for glucose, ions and other substances that cannot cross the membrane by simple diffusion Transport proteins have 3-D shapes that make them highly selective, recognizing atoms or molecules by shape, size or charge. http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.html

13. Two Types of Transport Proteins: • Carrier proteins – facilitate the diffusion of glucose across the cell membrane Q: Explain how glucose enters the cell. A: Glucose fits into a groove on the carrier (like a lock and key), the protein’s shape changes, and glucose is released on the inside of the cell. b) Channel proteins – have tunnel-like pores filled with water that allow charged ions in and out of the cell

14. Active Transport • …The movement of molecules and ions against the concentation gradient which requires ATP energy and carrier proteins to pump these molecules from an area of low solute concentration to an area of high solute concentration. (UP or against the concentration gradient) • used to accumulate nutrients, or remove toxic materials or wastes

15. Active Transport http://www.coolschool.ca/lor/BI12/unit4/U04L03/active%20transport_jeffedit.swf Most cells use 40% of their energy on active transport; kidney cells use 90% of their energy on active transport Example: Plants and potatoes

16. C. Bulk Transport - The use of vesicles to facilitate movement of substances that are too large to enter or exit the cell via transport proteins. Two types: • Endocytosis – the cell membrane forms a pocket around the material to be transported, then either pinches off as a vesicle or a vacuole. Q: Differentiate between a vacuole & vesicle. A:Vesicle transports contents; vacuole stores the ingested material.

17. Endocytosis Two Types of Endocytosis: • Phagocytosis – when cells “eat” by taking in large particles or other cells http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__phagocytosis.html Q: What happens after a new vesicle enters the cytoplasm of a cell? A:It fuses with a lysosome and the enzymes would digest the material b) Pinocytosis – when cells “drink: by taking in droplets of fluid

18. Endocytosis • Receptor – mediated endocytosis (RME) – receptors, like antennae, detect specific compounds or cells and bind with them, triggering endocytosis. • Q: Give 2 examples of molecules entering by RME • A: cholesterol & HIV

19. 2. Exocytosis • The reverse of endocytosis, whereby the membrane of vesicles or vacuoles fuses with the cell membrane and the stored contents are expelled from the cell. Q: Give 2 examples of expelled materials. A:wastes, enzymes, hormones http://highered.mcgraw-hill.com/olc/dl/120068/bio02.swf

20. Membranes At Work: Applications • Water Purification Reverse osmosis – uses pressure to force contaminated water through a membrane with fine pores that will not allow bacteria, salts, and other dissolved molecules through, resulting in water with fewer impurities.

21. Water Purification: Reverse Osmosis

22. Membranes At Work: Applications 2. Kidney Dialysis – filters toxic wastes that accumulate in the blood while retaining necessary proteins, glucose, amino acids & ions • The patient’s blood is pumped through dialysis tubing, a synthetic, semi-permeable membrane. • When immersed into a salt solution, needed salts don’t diffuse, but wastes, which are hypertonic to the dyalysate diffuse out of the blood.

23. Kidney Dialysis

24. Controlled Delivery of Medications • Medication can be placed in a flat transdermal patch that sticks to the skin. A semi-permeable membrane lining the inner surface allows drugs to diffuse out of the patch at a slow, constant rate. Q: give 4 examples of medications available in patches A: - nicotine, hormones, motion sickness drugs, contraceptives, pain reducers, weight loss

25. Controlled Delivery of Medications b) Liposomes – artificial vesicles that can safely transport medications from one part of the body to another Two Examples: • Used to transport anti-cancer medications to tumors in cancer patients • Liposomes, coated with the gene needed to cure cystic fibrosis, are sprayed into the patients nostrils