MR S1 Flashcards
What is the general composition of a membrane?
It varies between different membranes but the dry weight proportions are:
~40% lipid
~60% protein
~10% carbohydrate
What are the functions of membranes?
Selectively permeable barrier Control of the enclosed chemical environment Communication Recognition Signal generation in response to stimuli
In a hydrated membrane, what proportion of the weight is water?
~20%
What does amphipathic mean?
Molecule contains both hydrophobic and hydrophilic areas.
What is the structure of a phospholipid?
A glycerol molecule with two fatty acid side chains and a phosphate head
What effect would a double bond in a fatty acid side chain have?
The chain would have a kink
Describe the head chain of a phospholipid molecule
The head chain begins with a phosphate group which can have a variety of groups attached to it, for example: Choline Amine Amino acid Sugar
Describe the side chains of a phospholipid molecule
Fatty acid chain length can be between C14 and C24
Most common chain lengths are C16 and C18
Cis double bond creates a kink
What is a glycolipid?
Almost the same as a phospholipid, except the phosphate group is replaced with a sugar
What are the types of glycolipid?
Cerebrosides
Gangliosides
What is a cerebroside?
A glycolipid membrane molecule where the head group is a sugar monomer
What is a ganglioside?
A glycolipid membrane molecule where the head group is an oligosaccharide
How can individual phospholipid molecules move around the membrane?
Flip-flop
Lateral diffusion
Flexion
Rotation
What is the effect on the membrane as a whole of more cis double bonds in phospholipids?
Increased space between molecules/reduced packing
Describe the structure of cholesterol
Polar head group
Rigid planar steroid ring structure
Non polar hydrocarbon tail
What is the effect of cholesterol in membranes?
Maintains membrane fluidity in cold temperatures by preventing phospholipids from clumping together
Maintains membrane integrity and rigidity at higher temperatures by interacting with the side chains of phospholipids
Give an example of a phospholipid
Phosphtidylcholine
How can membrane proteins move around a membrane?
Lateral diffusion
Rotation
Conformational change
NO FLIP FLOP
What are the two types of membrane protein?
Integral - deeply embedded in the membrane
Peripheral - associated with the surface of the membrane
Describe peripheral membrane proteins
Only bound to the surface of the membrane by electrostatic or hydrogen bond interactions
May be easily removed by changes in pH or ionic strength
Describe intrinsic membrane proteins
Interact extensively with the lipid binding area of the phospholipid bilayer
Cannot be removed by pH or ionic manipulation, only by agents which compete for lipid interactions eg detergents
Why is asymmetrical orientation of proteins important?
A protein which interacts with the extra cellular environment would need to be correctly orientated in order to perform it’s purpose eg an insulin receptor would need to have its insulin binding site on the extracellular side of the membrane
What is the evidence for proteins in membranes?
Functional:
Ion gradients
Facilitated diffusion
Specificity of cell response
Biochemical:
Freeze fracture
Membrane fractionation
Gel electrophoresis
What are some restraints on membrane protein mobility?
Lipid mediated effects eg proteins tend to separate out in cholesterol poor regions
Membrane protein associations
Association with extra membranous proteins eg cytoskeleton
What types of amino acids are likely to be in a transmembranous domain of a protein?
HYDROPHOBIC
Small
Uncharged
What are haemolytic anaemias? Give examples.
Diseases where there is reduced oxygen carried in the blood due to increased breakdown of red blood cells
Can have many causes eg hereditary spherocytosis
Describe hereditary spherocytosis
Spectrin depleted by 40-50% Erythrocytes round up Less resistant to haemolysis Cleared up by the spleen Reduced erythrocyte lifespan Inability of bone marrow to adequately compensate causes haemolytic anaemia
Describe hereditary elliptocytosis
Defective spectrin formed Unable to form stable heterotetramers Fragile elliptoid cells Reduced cell lifespan Increased haemolysis Bone marrow unable to adequately compensate Anaemia
What is passive transport reliant on?
Membrane permeability
Concentration gradient
