introduction to cell membranes Flashcards
what is molecular cell biology: cystic fibrosis
-Mutations in CFTR (chloride channel) give rise to disease (DNA)
-Mutant proteins misfold (protein structure and function) CFTRdelta508
-Mutant proteins end up in the wrong location (intracellular trafficking)
-Disease presents in lungs and gastrointestinal tract (humans); gastrointestinal tract in mice (organismal physiology)
how do The appearance of biological membranes differ depending on location and function
-Myelin sheath (axon surrounds this) is formed from the plasma membrane of a Schwann cell (makes lots of plasma membrane around the axon)
what does the plasma membrane provide
-provides cell boundary and prevents movement of materials in to and out of the cell
what does the organelle membrane divide
-divide cytoplasm into compartments
what are the fundamental properties of membranes
-Barrier
-Flexible, self-repairing, continuous
-Selectively permeable
-Only certain molecules can pass into and out of cells
-membrane is very fluid so can withstand attempts of rupture
what is the membrane composition like
-The components of all membranes (prokaryotes, eukaryotes, plasma membranes or intracellular membranes) are basically similar
-lipids, proteins and carbohydrates- carbohydrates in which are normally always linked to lipids or proteins (glyco-)
-Oligosaccharide chains covalently linked to protein or lipid. Made up of sugar residues linked covalently in branched chains
how do phospholipids move about in the bilayer
-Phospholipids can rotate or exchange in the lateral plane of the membrane – but normally move very slowly from one leaflet to the other (flip-flop)
what does fluidity of the lipid bilayer depend on
-its composition
-different types of phospholipids
-if phospholipid has kinks it doesn’t pack as well
-number of double bonds and number of carbon atoms in the fatty acid chaos of phospholipids determine fluidity
-the greater number of double bonds and he shorter the acyl chains, the less tightly packed the molecules and the greater the fluidity- more unsaturated
what are some properties of the phospholipid bilayer
-Amphipathic
-Polar head group
-Hydrophobic tail
-have a glycerol back bone with a fatty acid chain
what are all membranes fluid at
-the temperature of the organism
-so plant and cold-blooded animal membranes: more double bonds and/or shorter acyl chains than membranes of warm blooded animals- therefore fluidity is always maintained
is phosphatidyl serine negatively or positively charged
-negatively
-one of the major membrane phospholipids
what does cholesterol do to the membranes
-its amphipatic
-makes membrane less permeable
-packs between phospholipid and makes the membrane less deformable at the surface
-it doesn’t make the overall membrane more rigid, only locally
-at high concentrations it stops the membrane from becoming crystalline
-less permeable to small molecules
-abundant in plasma membrane
-small oar head group
-non polar hydrocarbons tail
what kind of composition do bacteria cell membranes have
-simple phospholipid composition
-reflects the reduced number of functions they can do and the environments where they are found
how do hydrophobic and hydrophilic molecules act in aqueous solutions
-phospholipids are ampipathic
-acetone can form H bonds with water
-mehtyl-propane repels water and a crystalline lattice formed by water
how do lipids act in aqueous solutions
-form either micelles or bilayers
-micelles structure is circular, polar head groups facing outwards, hydrophobic tails facing inwards therefore protected against the aqueous environment
-Lipid bilayers prefer to form sealed compartments- because forming a concealed compartment is the most energetically favourable conformation for a bilayer
how are biological membranes organised
-bilayer structure
-sea of phospholipids
-proteins embedded in bilayer- for functions of cells
what do integral membrane proteins do
-directly insert in the membrane by a hydrophobic domain
-if you want to purify them: string detergents and high pH to extract from membrane
-anchored by alphahelices
what are Peripheral membrane proteins
-associate with integral membrane proteins or directly bind lipids
- covalently bound lipids which insert into the membrane
-Small G proteins have a fatty acid modification which allows them to cycle on and off membranes: Active on membranes, inactive in the cytosol
proteins in a sea of lipids
-Membrane lipids are not homogenous
-Can form clusters or microdomains- can self associate and self assemble
-proteins can be embedded in vesicles formed
what are the micro domains formed by cholesterol and sphingolipids
-rafts
-areas that are enriched with cholesterol- have saturated fatty acid chains which are thicker
-this accumulates proteins with longer anchoring transmembrane domains
what are the two domains in epithelial cells
-apical and basolateral
-protein compositions different in AM and BM
-tight junctions prevent movement between these membranes- also act as a diffusion barrier in extracellular leaflet domain but not intracellular
