Cell Membrane Flashcards
Fluid mosaic model
Fluid, molecules in constant motion
Mosaic, membrane looks like one when viewed from above due to protein molecules scattered throughout
Cholesterol
Lipid, controls membrane fluidity
More cholesterol, less fluid, less permeable membrane
Keeps membrane stable at normal body temperature so cells don’t lyse
Very hydrophobic, prevent water loss
Phospholipids in cell membranes
Barrier to most substances, helps controls entry and exit of materials
Smaller, less polar molecules enter more easily by diffusion across membrane
Small polar molecules diffuse slowly
Ions cannot diffuse through
Proteins in membranes
Integral, intrinsic, transmembrane proteins span width of membrane
Peripheral, extrinsic proteins confined to one side
Many are glycoproteins, have carb attached
Integral proteins
Carriers, channels
Transport substances, ions, sugars, amino acids which cannot diffuse through but still vital to cell functioning
Hormone receptors, neurotransmitters, enzymes for reaction catalysis
Peripheral proteins
Can be free on membrane surface, bound by integral protein
PP on extra cellular side, hormone receptor, neurotransmitter, cell recognition
PP on cytositic side, cell signalling, chemical reactions
Can dissociate into cytoplasm
Phospholipid bilayer
Main structure, allows small uncharged and lipid soluble molecules through simple diff
Makes membrane flexible, self sealing
Glycoprotein
Involved in cell recognition and immune response
Receptor for hormones, neurotransmitters
Helps cells attach to each other, form tissues
Glycolipid
Cell surface receptors for specific chemicals
Maintain membrane stability
Help cells attach to each other, form tissues
Protein receptor site
Allows other proteins to attach, enzymes, antigens, hormones
Protein channel
Filled with water, channel for water soluble ions to pass through, fac diff
Protein carrier
Shape change to move large molecules by fac diff
Molecule specific
How to prove the structure of the cell membrane
Experiments of Gorter and Grendel
Extracted phospholipids from surface membrane of RBC, spread out on trough of water
Formed layer, 1 molecule thick
Area=2x SA of RBC therefore bilayer
How can we prove the structure of the cell membrane?
Freeze fracture technique
Cells plunged into liquid nitrogen at -196 degrees
Frozen cell blocks pushed against razor blade
Fractures along weak points, middle of membrane
Some proteins can be removed without destroying membrane, others can’t
Therefore peripheral and intrinsic proteins exist
