Membranes 1 Flashcards
role as a barrier
prevents loss of required metabolites
Prevents entry of unwanted material
Other functions
capacitor: stores energy
Important for energy production and electrical signalling
Receives info, has a transduction signal within the cell
selective permeability
Maintain ionic comp: ion channels and transporters
Maintain cytoplasmic pH, osmotic pressure (aquaporins)
Sense environment- receptors
Anchor cytoskeletal structures
Mediate cell-cell and cell-ecm interactions
Carry out membrane requiring enzymatic reactions
What does it mean to say phospholipids are ampipathic
have hydrophilic head and hydrophobic tail
Bilayer
Lipids arrange so hydrophobic parts not in contact with water, and hydrophilic parts are
Energetically favourable to form sealed environment-bilayer joins at ends so edges are not exposed to water
glycerophospholipids
AKA phosphoglycerides
Based on 3C glycerol
2 fatty acid tails ester linked to -OH group of glycerol, and one -OH linked to phosphate
X (polar head group) attached to phosphate can be different
Different head groups give particular properties
Negative phosphate and OH positive groups on the head interact with water
X= choline
phosphotidylcholine
phosphotidyl
fatty acid part of glycerophospholipids
Glycolipids (sugar attached)
Sphingolipids
Sterols
cholesterol
phospholipids
glycerophospholipids, sphingolipids
When are lipids not phospholipids
don’t have phosphate eg some sphingolipids don’t have a phosphate
cholesterol
very small polar head group (OH)- rest of molecule is hydrophobic, and doesn’t have a phosphate- not PP
Although almost entirely HC, is amphiathic because OH interacts with water.
Absent from prokaryotic and plant cells
How are lipid bilayers fluid
PPs rotate freely, diffuse laterally and can move in flip flop motion from one leaflet to another
Flip flop- energy
less energetically favourable, as energy cost for moving hydrophilic/polar head group through hydrophobic environment- likely energy driven
Why is membrane fluidity important
Compromise between rigid, ordered structure and non viscous liquid
Allows for interactions in the membrane eg membrane proteins can assemble
Experiment for demonstration of membrane fluidity
Fuse mouse and human cell, different colours for membrane proteins- labels
Afetr incubating at 37 degrees for 40 mins, membrane proteins mix
Factors influencing membrane fluidity
- temp- more motion so membrane more fluid
- Saturation of fatty acid chains- kink in chain due to double bond means chains can’t pack as closely hence more fluid
- Length of acyl/FA chains
- cholesterol- decr fluidity. Rigid ring structure aids packing of lipids
Lipid asymmetry
Different composition in each leaflet
Some lipids ony found in cytoplasmic facing one, others eg glycolipids only found on etracellular leaflet
Cholesterol even across both
Eukary vs prokary lipid diversity
Eukary diversity greater
When in water PPs aggregate into
spherical micelles and liposomes, or bilayers
Type of structure aggregate into determined by
Length of FA chains, saturation and temp
Micelles rarely formed because
FA chains too bulky to fit
Sphingolipids
Derived from sphingosine, and contains a long chain FA attached in amide linkage to sphingosine amino group
Some sphingolipids have phosphate based polar head group, some are amphipathic glycolipids, whose polar head groups are sugars and not linked via a phosphate group
