Week 3: Membrane Mobility Flashcards
What structure does biological memmbrane have?
Liquid crystal structure
Lipid crystal structure
Lipid are close packed and relatively high ordered - but free to move in some directions
What does cooling the membrane result in?
Phase transition
What does the barrier function of the cytoplasmic membrane depend on,
Physical state of lipid bilayers
At lower temperature what happens to the membrane lipid bilayers ?
Undergo a reversible change of from fluid to a non fluid array of fatty acyl chains
What does changing growth temperature trigger?
Cell responses that change the lipid composition of membranes
What is phase transition?
Temperature required to induce a change in lipid physical state from ordered gel phase to disordered liquid crystalline phase
What factors control membrane fluidity?
1) saturation/desaturation of fatty acids 2) cholesterol content 3) temperature
saturation/desaturation
Introduces bends - desaturated Lipids cannot pack so closely and do not form gels so easily Lipids with shorter chains are less stiff and less viscous Make tails more rigid - cannot rotate easily (membrane more fluid). Phase transition temperature is lowered
Cholesterol content
Disrupt packing of fatty acid chain and inhibit the formation of gel state Widens the range at which the membrane stays fluid. Bidirectional regulator At high temperature: stabilises the membrane and raises its melting point Lower temperature: it intercalates between phospholipids and prevent them from clustering together and stiffening
Temperature
Heats up the membrane Lipids require thermal energy when heated; energetic Lipids move around more, arranging and rearranging randomly, membrane more fluid
What does Cyanobacterium lack the genes for?
Coding for desaturates
Desaturases
Enzyme that introduce double bonds into fatty acids
Why is membrane fluidity important ?
1) it allows membrane proteins rapidly in the plane of bilayer 2) it permits the membrane Lipids and proteins to diffuse from sites where they are inserted into bilayer after their synthesis 3) it enables membrane to fuse with one another and mix their molecules 4) it ensures that membrane molecules are distributed evenly between daughter cell when a cell divides 5) necessary to allow diffusion and dynamic interaction of proteins in the membrane (cell signalling) 6) diffusion of other membrane compartment 7) membrane assembly
What can lipid bilayer exist as?
Relatively fluid state
How can phospholipid move?
Laterally within the same leaflet with considerable ease
How can the mobility of individual Lipids molecules within bilayer of plasma membrane be observed?
Under microscope by linking the polar heads of the lipid with gold particles or fluorescent compounds
What is the half-life of a phospholipid molecule moving across to the other leaflet measured?
Hours to days
What movement of phospholipid is more restricted?
Flip flop to other side of the membrane
How does flip flop occur?
The hydrophilic head group of lipid must pass through the interval hydrophobic sheet of membrane which is thermodynamically unfavourable?
What enzymes actively move certain phospholipids from one leaflet to the other?
Flippases
What does the enzyme establish?
Lipid asymmetry and reverse the slow rate of passive transmembrane movement
What are the heterogeneity in Membranes?
1) Asymmetric distribution of Lipids in the two bilayer leaflets 2) different lipid composition of different cellular membrane systems 3) patchy distribution of proteins and Lipids e.g. lipid rafts
What does the lipid bilayer consist of?
Two distinct leaflets that have a distinctly different lipid composition
