ICPP 1 Membrane Bilayer - Lipids Flashcards
What are functions of the membrane?
Highly selective barrier
Control of enclosed electrochemical environment
Communication
Recognition
Signalling
Adhesion protein
Immune surveillance - communication
Signal generation to response to stimuli
What is the membrane composition by dry weight?
40% lipid
60% protein
1-10% carbs
How much of membrane weight is water?
20%
Role of water in membranes
Interacts with charged/polar regions + stabilises lipid head regions
What are the types of lipids?
Glycolipids
Cholesterol
Phospholipids - saturated + unsaturated
Types of unsaturated chains
Cis - kink
Trans - straight leg
What type of chain will make the membrane more fluid and why?
Cis unsaturated chain
Less tightly packed together due to kinks
Amphipathic meaning
Includes both hydrophobic + hydrophilic parts
Composition of phospholipid
Hydrophilic phosphate head + polar group
Glycerol backbone
Hydrophobic fatty acid tails
What type of reaction is between the fatty acid tails + glycerol back bone in phospholipids?
Esterification reaction
What enables phospholipid head + tails to rotate?
Glycerol residual has single bonds
Types of polar groups attached to the phosphate head in phospholipids
Amines
Amino acids
Choline - most common
Inositol - source of secondary messanger
What makes phospholipids optimally energetically stable?
External hydrophilic head
Internal hydrophilic tails
What is a sphinogomyelin?
Phospholipid without glycerol backbone
Has a sphingosine molecule instead
How are sphinogomyelin synthesised?
Bringing together a fatty acid chain + sphingosine molecule
What do sphingosine molecules have?
Serine residual -NH group
What can be the head group in sphinogomyelins?
Choline
Ethanolamine
What are the fatty acid chains mainly in sphinogomyelins?
Mainly saturated FA
If unsaturated FA > trans > no kink > closer packing
Function of sphinogomyelins
Membrane protein orientation
Formation of lipid rafts
Composition of sphinogomyelins
Head group - choline or ethanolamine
Sphingosine molecule
Fatty acids - mainly saturated
Composition of glycolipids
No phosphate had
No glycerol backbone - sphingosine molecule instead
Fatty acid chains
Where are glycolipids located?
What for?
Only on external membrane for signalling
Classes of glycolipids
Cerebrosides
Gangliosides
Head group in cerebroside
Glucose
Galactose
Where is there a high concentration of sphinogomyelins?
Myelin sheath
Where is there a high concentration of cerebrosides?
Myelin sheath
Nervous system
Function of cerebrosides
Stabilises membrane
Cell to cell recognition
Form basis of blood group - antigens on RBCs
Lipid raft formation
What is connected to the head group in gangliosides?
Oligosaccharide chain
Function of gangliosides
Cell-cell signalling
Immune system - important in CNS
Lipid raft formation
Where are gangliosides on membranes?
Extend out from cell surface
What are steroids derived from?
Cholesterol
Composition of cholesterol
-OH head - hydrophilic
Non-polar hydrocarbon tail - hydrophobic
Function of cholesterol
Membrane fluidity control
Lipid raft formation
Extending temp rang of membrane
Relationship between permeability of membrane + structural integrity
Reciprocal
Increase in permeability = decreased in structural integrity + vice versa
List the ways lipids can move
Fast axial rotation
Fast lateral diffusion
Protrusion
Wave 3D undulations
Flip flop
Describe fast axial rotation
Whole lipid spins on head-tail axis
In circles
Describe fast lateral diffusion
Lipids move randomly side to side through bilayer
Describe protrusion
Bobbing up + down on vertical axis
Describe wave 3D undulations
Like Mexican wave
Describe flip flop movement
Lipid flips upside down
What does adding unsaturated phospholipids to the membrane do?
Increases fluid using due to cis chains
Less close packing
Gel/fluid state
What does adding unsaturated phospholipids to the membrane do?
Increased membrane stability
Acts as a buffering molecule - extends temp. range
What are lipid rafts?
Areas of organised/specialised distribution of lipids
Components of lipid rafts
Cholesterol
Sphinogomyelins
Saturated glycolipids
Function of lipid rafts
- Provides more stable environment for signalling proteins
- Stabilises + organises proteins
- Acts as organising domain for receptors or signalling molecules
- Optimises kinetic interaction for signal transduction
What features does the components of lipid rafts allow?
Strong interaction > tight packing > decreased movement + fluidity
What is there a reduced amount of in lipid rafts?
Unsaturated chain phospholipids
