Transport across membranes
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Transcript of Transport across membranes
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Transport across Transport across membranesmembranes
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
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Metabolism and cell survivalMetabolism 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?
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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
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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.
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Factors that affect Rate of Diffusion Factors that affect Rate of Diffusion across a membraneacross a membrane
• Temperature• Concentration gradient• Surface area of the membrane• Distance/thickness of the
membrane• Size of molecules
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Diffusion in cellsDiffusion in cells
Passive (simple) Diffusionhttp://www.youtube.com/watch?
v=s0p1ztrbXPY&feature=related
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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
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Which Which is is
which?which?
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http://www.stolaf.edu/people/giannini/flashanimat/transport/channel.swf
Copy blue box bottom of page 23
Gated and non gatedGated and non gated
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Active TransportActive Transporthttp://www.stolaf.edu/people/giannini/fhttp://www.stolaf.edu/people/giannini/f
lashanimat/transport/channel.swflashanimat/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
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See how Active Transport happens!
• YouTube - Active Transport
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Endo- and Endo- and ExocytosisExocytosis
Used for bulk transport
Complete notes by reading through
p25
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See how Endocytosis and Exocytosis happen
YouTube - Cell Membrane, Exocitosis & Endocitosis
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Cell signallingCell 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)
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For cover work: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