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
Plasma membrane:
Separates cell contents from external environment
Controls what passes between cell and environment
Partially permeable
Phospholipid bilayer
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
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
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

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Chapter 2
Receptor in plasma membrane interacts with Gprotein
Gprotein = activated
Activates enzyme
Causes response in cell
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
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
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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