Transport across membranes

1. Transport across membranes By the end of this lesson you should be able to describe how the components of a membrane allow both passive and active transport of molecules into and out of cells

2. Metabolism and cell survival • Reactions in living cells require molecules to be transported into the cells. • Some reactions make useful products that need to be transported out of the cells • Many reactions produce waste products that need to be removed from the cells. • All molecules that need to pass into or out of a cell will have to pass across a membrane. • How do you think this happens?

3. Types of transport • Simple Diffusion • Facilitated diffusion through “channel” proteins • Facilitated diffusion through “carrier” proteins • Facilitated diffusion through “gated” proteins • Active transport which requires energy in the form of ATP

4. Diffusion • The NET movement of molecules from an area of high concentration to an area of low concentration • This means that molecules are moving randomly in all directions but the final outcome appears to be in one direction.

5. Factors that affect Rate of Diffusion across a membrane • Temperature • Concentration gradient • Surface area of the membrane • Distance/thickness of the membrane • Size of molecules

6. Diffusion in cells Passive (simple) Diffusion http://www.youtube.com/watch?v=s0p1ztrbXPY&feature=related

7. Simple diffusion through the phospholipid bilayer • Lipid based molecules can slip through the hydrophobic core and passively move down the concentration gradient • Very small or non-polar molecules E.g. Oxygen, carbon dioxide and water can easily pass through the bilayer • Larger or charged molecules cannot pass between the phospholipids, so they require help through facilitated diffusion • Channel proteins: gated or ungated ‘pores, Ungated pores are always open, Gated pores need another substance to bind to them to open the gate. • Carrier proteins: These are “molecule-specific” carriers that change shape when activated to allow passage through the membrane

8. Which is which?

9. Gated and non gated http://www.stolaf.edu/people/giannini/flashanimat/transport/channel.swf Copy blue box bottom of page 23

10. Active Transporthttp://www.stolaf.edu/people/giannini/flashanimat/transport/channel.swf • When concentration gradients can’t help! • Find 2 examples • ‘Pump’ like carrier protein • Complementary shape to molecule • Require ATP • Go against concentration gradient • Can transport at a faster rate than diffusion • Molecules can be accumulated on either side of a membrane

11. See how Active Transport happens! • YouTube - Active Transport

12. Endo- and ExocytosisUsed for bulk transportComplete notes by reading through p25

13. See how Endocytosis and Exocytosis happen YouTube - Cell Membrane, Exocitosis & Endocitosis

14. Cell signalling • Signalling and receiving signals is vital for cell survival and communication • When looking at the bilayer, chains ‘sticking out’ from the surface are visible (called?) • These allow for ‘self’ recognition of cells by the immune system, to prevent auto immune responses • The surface also has membrane bound receptors associated with these projections that are modified protein molecules. • They receive ‘messages’ about cell activities via chemical messengers (called?) • Like jigsaw pieces a hormone and receptor will only bind with their complementary partner causing the target cell to respond. (similar idea to enzyme active site and substrate)

15. For cover work: Research in as much detail as you can the communication and cell signalling involved with: • Insulin • AIDS • BOTOX and • Beta blockers Please use p20-21 to help guide you and help you begin your research