The Membrane Bilayer Flashcards
What are 5 functions of the membrane bilayer?
- Continuous highly selective permeable barrier
- Control of enclosed chemical environment
- Communication - control the flow of information between cells and their environment
- Recognition: signalling molecules, adhesion proteins and immune surveillance
- Signal generation in response to stimuli - electrical/chemical
What is the composition of the membrane in terms of dry weight
40% lipid
60% protein
1-10% carbohydrate
What is the purpose of the Cis double bond in membrane lipids
Introduces a kink that reduces phospholipid packing
What is a cerebrosides and gangliosides
Cerebrosides: glycolipid with head group sugar monomer
Ganglioside: glycolipid with head group oligosaccharides
What are the 4 phospholipid motions
- Intra-chain motion
- Fast axial rotation
- Fast lateral diffusion
- Flip-flop (rare) - requires energy
What are the actions of cholesterol in the plasma membrane
Increases fluidity by reducing phospholipid packing
Decreases fluidity by reducing phospholipid chain motion (H-bonding between head ends)
What is the motility of proteins in membranes
Conformational change
Rotational and lateral
Mobility restrained due to association with other proteins
What is the biochemical evidence for proteins in the membrane
Membrane fractionation and gel electrophoresis
Freeze fracture
What is the functional evidence for proteins in the membrane
Facilitated diffusion
Ion gradients
Specificity of cell responses
How are peripheral membrane proteins bound to the surface
Electrostatic and hydrogen bonds
How can peripheral proteins be removed from the membrane and what is this evidence for
Changes in pH or ionic
Shows that the proteins are not embedded
How are integral proteins associated with the membrane
Interact with hydrophobic domains of the lipid bilayer
How can integral proteins be removed from the membrane
They are not removed by changes in pH or ionic strength
Removed by agents that compete for non-polar interactions e.g. detergents
What is the erythrocyte skeleton a network of
Spectrin and actin molecules
What is the structure of spectrin
Rod-like with alpha and beta subunits wound together to form an anti-parallel heterotetrama alpha2beta2
How are the spectrin molecules held onto the membrane?
By ankyrin, band 4.1, band 3 and glycophorin A
What is hereditary spherocytosis and what happens
Disease where spectrin levels are decreased to 40-50%
Cells become more rounded and therefore are less resistant to lysis when passing through capillaries
Patients are easily fatiguable
What is the treatment for hereditary spherocytosis
Blood transfusion
What is hereditary elliptocytosis
Defect in spectrin which prevents heterotetramers from forming which causes ellipsoid shaped cells
What recognises the signal sequence of a protein
Signal recognition particle (large protein/RNA complex)
What happens when the signal sequence is bound to SRP
The ribosome locks the ribosome complex and prevent further protein synthesis in the cytoplasm
What recognises the SRP on the ER
SRP receptor/docking protein
What happens once the SRP is released from the signal sequence
The signal sequence interacts with the signal sequence receptor (SSR) within the protein translocater complex in the ER membrane
How is passage of the protein through the membrane arrested
There is a stop transfer signal - highly hydrophobic primary sequence of 18-22 aa (transmembrane domain)
