Exchange with the Environment

1. Exchange with the Environment Cell Transport

2. Cell Processes • For a cell to survive, it must get nutrients and water. It must also get rid of wastes • How can the cell get materials in and out through the cell membrane?

3. Cell membrane • Made up of a phospholipid bilayer and several proteins • Phospholipid: • Hydrophillic phosphate head • Hydrophobic fatty acid tail Image from: http://academic.brooklyn.cuny.edu/biology/bio4fv/page/phosphb.htm

4. Cell membrane

5. Cell membrane: Proteins • Integral Proteins • Embedded in lipid bilayer • Receptor proteins and transport proteins • Transmit signal or materials into/out of the cell • Peripheral Proteins • Only on one side of membrane • Some act as enzymes • Some act as cell markers

6. Fluid mosaic model of cell membrane • Phospholipid bilayer acts as a fluid • Lipids and proteins can move in the layer • Sterols (including cholesterol) are used to help keep membrane structure

7. Cell membrane

8. Cell Membrane

9. Diffusion • The movement of particles from an area of high concentration to an area of low concentration down the concentration gradient • Occurs outside of cells and across cell membranes

10. Diffusion Picture from: http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/diffus.html

11. Osmosis • The diffusion of water across a cell membrane • If solution outside a cell has more water than the cell then water will move into the cell

12. Osmosis Image from: http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/diffus.html#c3

13. Movement of small particles • Not all particles are able to slip through a cell membrane through diffusion • Example: sugars and starches aren’t small enough to move between the phospholipid molecules

14. Types of solutions • Isotonic • Has same concentration as a cell, the cell neither loses nor gains water • Hypotonic • Has less concentration than cell, cell gains water

15. Types of solutions • Hypertonic • Has more concentration than cell, cell loses water

16. Osmosis in cells • Paramecia • Control water flow by using a contractile vacuole • Collect excess water and pump it out of the cell • Plant cells • Live in hypotonic environment • Survive because of cell wall • Pressure of water against cell wall: turgor pressure • Too much water leaves the cell: plasmolysis • Water storage in Central Vacuole

17. Transport of particles • Some particles have to go through “doorways” to enter the cell • Because they are too large or not soluble through cell membrane • These “doorways” are protein channels • These proteins are carrier proteins

18. Facilitated Diffusion • Diffusion of particles through protein channels in a cell membrane • Particles move from high concentration to low concentration • Example: glucose and salts • Does NOT require energy

19. Image from: http://www.bios.niu.edu/sims/metabolism/metabolism1.htm

20. Ion Channels • Allow ions to move across the cell membrane • Specific to specific ions • Some are “gated”

21. Active transport • Movement of particles against the normal direction of diffusion • Particles move from LOW concentration to HIGH • Requires energy from the energy molecule ATP • Example: sodium/potassium pump

22. Image from: http://www.cat.cc.md.us/courses/bio141/lecguide/unit1/prostruct/images/u1fig7a.jpg

23. Image from: http://www.sp.uconn.edu/~terry/images/anim/antiport.gif

25. Moving larger particles • Endocytosis • Cell membrane surrounds a particle, and encloses it in a vesicle • Phagocytosis • When large particles are taken in by endocytosis • Pinocytosis • Transport of fluids or solutes

26. Image from: http://www.sirinet.net/~jgjohnso/endocytosissmall.jpg

27. Endocytosis Image from: http://www.sp.uconn.edu/~bi107vc/images/cell/clathrin.jpg

28. Exocytosis • Used to remove large particles from the cell • Vesicles formed at the ER or Golgi move to the cell membrane for release

29. Exocytosis Image from: http://www.sirinet.net/~jgjohnso/exocytosis.jpg

30. Image from: http://cellbio.utmb.edu/cellbio/end7.jpg

31. Modeling the cell membrane