Lecture 1: Lipid Bilayers Flashcards
What is the basis of biological membrane?
Lipid bilayer
What does the membrane separate?
Two watery aqueous state - cytoplasm and extracellular fluid
What domains do lipid contain?
Hydrophobic domain and hydrophilic domain
What is hydrophibicty?
Non-polar molecules which repel water 1) non polar substances clump together rather than distributing in water 2) entropic effect - disruption of hydrogen bonds between molecules
What is hydrophilic?
Having affinity for water Readily dissolving in water Polar
What does water molecules make with polar/charged molecules?
Stable interactions
How do phospholipid react to water?
The hydrophilic head faces the water while we hare hydronic tail faces away from water
What is a lipid vesicles?
Continuous bilayer with water on the inside and outside
What are the basic properties of lipid bilayers?
Self-assembling/self-repairing Flexible Fluid Form permeability barriers Tend to enclose aqueous compartments Able to pinch off and reseal
Self-assembling
If lipid is in the right environment you can spontaneously form a bilayer (no energy required) Bilayer only works in the presence of water You can take the structure apart by using organic solvents (lipid bilayer will disintegrate)
Flexible
Fluid nature allows them to wobble and wave Allow for growth, division and changing shape
Fluid
Weak VDW
Forces will mean lipids can exchange places
Self-repairing
Deal up a hole in the bilayer, hole will fill up to prevent the interaction of hydrophobic tails with water
Permeability barriers
Continuous bilayer Steroid hormone/ oestrogen/ testestorone - non polar molecules where they act on the nucleus of the cell - bind to the reception - change in gene expression Polar molecules: sugar, ATP
Tend to enclose aqueous compartments
Prevent exposed edges, ends will join
Able to pinch off and re-seal
Splitting the vesicles into 2 (not always energetically favourable as have to break it first)
What does the lipid bilayer or plant cell separate?
Interior of the Golgi or ER from cytoplasm - make a barrier between two aqueous compartments
Experiment - Gorter and Grendel
Classic experiment that convinced the world that membranes were based on lipid bilayers RBC surface area will be calculated to see the total size of the cell Extract lipid from the cells of RBC - dissolve in organic solvents Lipids will separate from other cell organelles Put a drop of lipid in the pipette Lipids are spread out on surface of water with their hydrophilic heads in contact with water and non polar hydrophobic tail sticking out in the air Lipid solution will make a mono layer on surface of liquid
Calculate area covered by the mono layer on RBC. Surface area of mono layer formed was twice as big as the RBC total surface area
What was problems associated with GG experiment?
Surface tension of the model was greater than surface tension of actual membrane There are different membrane compartments in the cell of animal
Davson and Danielli
Describe the position of proteins within bilayer Membranes exhibit a characteristic “trilaminar” appearance - 3 layers (2 dark outer layers and a lighter inner region) The cell membrane is made of a phospholipid bilayer sandwiched between 2 layers of globular proteins The polar (hydrophilic) heads of phospholipid are orientated towards the protein layers forming a hydrophilic zone The non polar tails of phospholipid are orientated in between polar bears forming a hydrophobic zone
What are problems associated with DD experiment
Not all membranes are identical or symmetrical Membranes with different function also differ in chemical composition and structure Membrane are biracial with distinct inside and outside faces A membrane with an outer layer of proteins would be an unstable structure Membrane proteins are not soluble in water and like phospholipid are amphiphatic
What was observed in a Freeze fracture (electron microscopy) ?
Proteins were embedded and not laying on the outside of the membrane and proteins were globular structures Proved that proteins are hydrophobic, folded, made bigger lumps, proteins are spread everywhere Shower that proteins are able to move about the membrane
What is Freeze Fracture ?
Specialised preparation technique that splits the plasma membrane along the middle of the phospholipid
What is the fluid mosaic model?
Membranes are composed of phospholipid bilayer with various protein molecules floating around within it
Mosaic
The phospholipid bilayer is embedded with proteins, resulting in a mosaic of components
What are he properties of fluid mosaic model
Partially hydrophobic System is fluid
Singer and Nicholson
Current model of plasma membrane
Phospholipid
Main fabric of the membrane
Cholesterol
Attached between phospholipids
Integral proteins
Embedded within the phospholipid layers
Peripheral proteins
On the inner or outer surface of the phospholipid bilayer; not embedded within the phospholipids
Carbohydrates (glycoproteins and glycolipids)
Generally attached to proteins on the outer membrane layer
How are mitochondria a bacteria ?
They have their own membrane which can be sequenced
Mitochondria and chloroplast in plant cell started out as bacteria, what happened next?
Symbiosis in the cytoplasm
What is symbiosis?
When two different species benefit from living and working together
In what conditions can few mitochondria live?
Anaerobic conditions
