Cell membranes: Summary notes

My summary notes from last year on cell membranes

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  • Created by: sxrcha
  • Created on: 17-10-15 14:28
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Chapter 2
Cell Membranes ­ Summary Notes
Structure
Plasma membrane:
Separates cell contents from external environment
Controls what passes between cell and environment
Partially permeable
Phospholipid bilayer
Membranes:
Produce different compartments within cells
Important in cell signalling
Allow electrical signals to pass along them
Provide attachment site for enzymes/other molecules in metabolism
Phospholipid bilayer:
Heads ­ tiny charge ­ attracts them to water molecules ­ hydrophilic
Tails ­ no charge so repelled ­ hydrophobic
Heads face outwards ­ in contact with watery cell contents
Tails face inwards ­ not in contact with water
Cholesterol:
Molecules lie alongside phospholipids
Help to make up bilayer ­ maintain fluidity
Cell membrane:
Contains protein molecules ­ larger than phospholipids
Some proteins lie in membrane ­ protruding from sides
Others float in outer/inner layer
Lipid and protein molecules ­ short strings of sugar molecules attached ­ form
glycolipids and glycoproteins
Fluid mosaic model:
Structure of membrane
`Fluid' ­ molecules in constant motion
`Mosaic' ­ protein molecules scattered throughout
Phospholipid ­ provides barrier to hydrophilic substances
Protein/glycoproteins:
Form channels ­ open and close ­ allow hydrophilic substances through
Transporters ­ move substances across membrane (up conc. gradient using
energy from ATP)
Receptor sites ­ allow molecules outside (e.g. hormones) to bind, set up
responses in cell
Recognition sites ­ structure specific to particular individual
Act as enzymes
Cell signalling
Signal = chemical that attached to protein/glycoprotein ­ acts as ion channel
Method:

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Chapter 2
Receptor in plasma membrane interacts with Gprotein
Gprotein = activated
Activates enzyme
Causes response in cell
Method:
Receptor is also an enzyme ­ contains 2 parts
Signal molecule slots into both parts
Connection forms active enzyme
Enzyme causes response in cell
Membrane processes
Passive processes ­ don't require energy ­ diffusion, facilitated diffusion, osmosis
Active transport ­ substances move up conc. gradient ­ requires energy
Diffusion:
Net movement of molecules/ions down concentration gradient
Hydrophobic, nonpolar
Oxygen ­ diffuses into cell due to conc.…read more

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Chapter 2
Endocytosis:
Moving substances into cell
E.g. Phagocyte engulfing bacterium
Cell extends `fingers' of cytoplasm around bacterium
Fuse to form complete ring ­ vacuole
Enzymes secreted in to digest bacterium
Process can move liquid into cell
Exo/endocytosis ­ both active processes ­ require energy
Membrane permeability:
Affected by temperature
E.g.…read more

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