Flashcards in Membranes And Receptors 1 Deck (91)
What specialised function does a mitochondrial membrane have?
Energy conservation by oxidative phosphorylation
What approximately is a membrane's dry weight composition?
What is the normal percentage composition of water in a hydrated membrane bilayer?
Define an Amphipathic molecule?
A molecule (especially a protein) containing both hydrophilic and hydrophobic moieties
Describe the general STRUCTURE of a phospholipid
1. Two Fatty acid chains, attached to a...
2. Glycerol back-bone
3. Phosphate + head group (changeable) attached to the glycerol
A phospholipid is described as Amphipathic. Explain why in terms of its structure.
Phospholipids contain both hydrophilic and hydrophobic moieties:
1. Hydrophilic - polar head group and attached phosphate
2. Hydrophobic - fatty acid tails
A range of polar head groups are found in phospholipids. List four:
There are an enormous range of fatty acids found in phospholipids. What chain lengths are most commonly found?
What are the 5 general functions of a biological membrane (cell and organelle membrane)?
1. Highly selective permeability barrier
2. Controls enclosed chemical environment
3. Controls communication - flow of information between cells and their environment
4. Recognition - signalling molecules, adhesion proteins, immune surveillance
5. Signal generation in response to stimuli - electrical or chemical
What is the effect of cis double bonds in unsaturated fatty acid chains of phospholipids on phospholipid packing?
It introduces a kink in the fatty acid chain which decreases phospholipid packing
Which type of phopsholipid is not based on glycerol? What is it based on instead?
Shingolipids - they are based on aliphatic amino acids e.g. sphingosine
If you replace a phosphocholine moiety with sugar what type of molecule do you get?
Describe the structure of a glycolipid
Lipid residue -glycerol or sphingosine backbone with FA chains
Carbohydrate residue - lipid residue bound to a monosaccharide or oliogosaccharide by a glycosidic bond
What do you call glycolipids which have head groups consisting of sugar monomers?
What do you call glycolipids which have head groups consisting of oligosaccharides?
What proportion of total membrane lipid content is cholesterol?
What is the conformation of sphingomyelin like in relation to other phospholipids in the membrane?
It resembles other phospholipids - often has a phosphocholine head group
What is the favoured structure of phospholipids and glycolipids in aqueous media?
How is a biliayer formed by phospholipids and glycolipids in aqueous media?
Spontaneously - driven by Van der Waals forces between their hydrophobic tails
How are lipid bilayers stabilised?
By non-covalent forces- electrostatic and hydrogen bonding between hydrophilic moieties and between hydrophilic groups and water
What do pure lipid bilayers have a very low permeability to?
Ions and most polar molecules
What are the four modes of mobility in a lipid bilayer?
1. Intra-chain motion
2. Fast axial rotation
3. Fast lateral diffusion within the plane of the bilayer
Describe 'intra-chain motion' of a lipid in a bilayer
The formation of kinks in the fatty acyl chains
Describe 'axial rotation' of a lipid in a bilayer
Rotation of a phospholipid around its own axis
Describe 'flip-flop' movement of a lipid in a bilayer
The movement of lipid molecules from one half of the bilayer to the other, on a one-for-one exchange basis
What is the effect of unsaturated double bonds in the fatty acid side chains of phospholipids on the dynamics of the lipid bilayer?
They disrupt the hexagonal packing of phospholipds and therefore increase membrane fluidity
List some of the roles of membrane proteins
enzymes, transporters, pumps, ion channels, receptors and energy transducers
What is the normal dry weight of protein in membranes and why can this vary?
Normally it is approximately 60%. This can vary depending on the function of the membrane e.g. there is only 18% in myelin (causing increased electrical resistance) and 75% in mitochondria
What are the three modes of motion permitted for proteins in bilayers?