The Membrane Bilayer : Main biophysical properties Flashcards
What is the function of Biological membranes?
- Continuous, highly selective permeability barrier
- Control of the enclosed chemical environment
- communication
- recognition
- signal generation
What is the composition of membrane?
- 40% lipid
- 60% protein
- 1-10% carbohydrate
Describe properties of lipid bilayer
- Forms a bilayer spontaneously in water
- van der Walls forces between hydrophobic tails
- electrostatic and hydrogen bonding between hydrophilic heads
- interaction between hydrophilic groups and water
What are amphipathic molecules?
They contain both hydrophilic and hydrophobic moiety
Describe the phospholipid molecule
Head group :
- range of polar head groups
- eg. choline, amines, sugars
Fatty acid chains :
- mostly C16-18 long
- Cis double bonds - kinks
What is sphingomyelin?
only phospholipid not based on glycerol backbone
What is the function of glycolipids?
Form H bonds with water to stabilize membrane structure
State the characteristics of glycolipids
- sugar containing lipid
- cerebrosides : head group sugar monomer
- gangliosdes : head group oligosaccharide
What is the important role played by cholesterol in plasma membrane?
stabilises plasma membrane
State the characteristics of cholesterol
- polar head group
- rigid planar steroid ring sturcture
- non-polar hydrocarbon tail
What is the function of cholesterol in maintaining fluidity of membrane?
High temp
- reduces fluidity
- reducing phospholipid chain motion
Low temp
- increases fluidity
- reduces phospholipid packing
What is meant by fluid membrane?
phospholipid bilayer with protein molecules floating around freely within it
What are the different membranes that have specialised functions?
- Microvilli : absorption of nutrients
- Neural membrane : electrica signal conduction
- Goblet cell membrane : secrete mucus
How does unsaturated double bonds in f.a side chain increases membrane fluidity?
They disrupt the hexagonal pacaging of phospholipids
Why does flip flop uses a lot of energy?
Movement of lipid molecules from one half of the bilayer to the other involves passing through hydrophobic and hydrophilic regions
Why small polar molecules like water can diffuse through lipid bilayer but smaller substance like H+ cannot?
Non polar molecules
- Hydrophobic and non polar molecules diffuse across bilayer at rate porpotional to size
Polar molecules
- charged nolecules complex water around them
- become too large to cross
Water
- water in middle of extremes
- diffuse at rate proportional to size and polarity
List the type of mobilities of lipid in lipid bilayer
- Intra chain motion - kink formation in fatty acid chains
- fast axial rotaion
- fast lateral diffusion
- Flip flop
