Membrane Bilayer Flashcards
How does the membrane bilayer respond to stimuli?
It generates chemical or electrical signals.
Name the constituents of the plasma membrane.
40% lipid and 60% protein. It can also be 1-10% carbohydrate but this varies.
Where in the bilayer is water found?
Water molecules are hydrogen bonded to the surface of the bilayer. It is a hydrated structure where 20% of the weight is water.
What is a phospholipid?
It is a glycerol molecule with two fatty acid molecules attached and a phosphate group.
Name molecules which can be the head group of a phospholipid.
Amines, amino acids, choline and sugars.
State some properties of the fatty acid chains in a phospholipid.
They are usually C14-C24 and predominantly C16-18. This means that the bilayer has a fairly constant thickness. Cis double bonds introduce a kink into the tail.
Name a phospholipid not based on a glycerol backbone.
Sphingomyelin.
What is a glycolipid?
This is where we replace the phosphocholine moiety with a sugar.
What is the difference between a cerebroside and a ganglioside?
These are both glycolipid a but a cerebroside only has a single sugar residue whilst a Ganglioside has multiple sugar residues.
What movements can phospholipids undergo within a phospholipid bilayer?
Flip flop (rare) as has to move through hydrophobic domain
Lateral diffusion
Rotation
Flexion
What do double bonds in a fatty acid chain do to the membrane?
They limit the close packing of the molecules and therefore cause increased fluidity of the membrane.
Describe the structure of Cholestrol.
It is a rigid molecule with a polar head group.
State how Cholestrol can increase membrane fluidity.
It reduces phospholipid packing
State the effect that cholestrol has on phospholipid chain motion
It reduces it, therefore reducing membrane fluidity.
What method can we use to find out about the proteins present in a membrane?
Freeze fracture, then gel electrophoresis.
Explain the principle of freeze fracture.
This is where the membrane is surrounded by ice. It is then broken. It will break at the weakest point and this is between the two lamellae.
State the functional properties of the proteins in a membrane.
Facilitated diffusion, ion channels and gradients, ensure specificity of cellular responses.
How can proteins in the membrane move?
Conformational change, lateral diffusion and rotation.
Why can’t proteins flip flop?
They are too large molecules and there is not sufficient energy to move the, through the hydrophobic domain in the membrane.
What can prevent protein movement within a membrane?
Aggregations, tethering (to basement membrane or to internal structure), interactions with other cells.
What are the lipid mediated effects on proteins in the membrane?
This is the fact that proteins in the membrane will tend to spread out to regions where there is poor Cholestrol.
How can peripheral proteins be removed from a membrane bilayer?
Peripheral proteins are only bound by H bonds and electrostatic forces. This means that they are affected by changes in pH and ionic strength and can be removed.
What type of proteins interact with the hydrophobic domain of the membrane bilayer?
Integral proteins. These can only be removed by organic solvents or detergents.
State two properties of transmembrane peptides.
They tend to be 18-20aa in length and predominantly a helix with hydrophobic r groups.
What does a hydropathy plot show?
Areas of hydrophobia and hydrophilia
What is membrane protein topology?
This is the importance of the proteins beings in the correct orientation in the membrane to ensure that they are functional.
What is the erythrocyte cytoskeleton made up from?
A network of spectrin and actin molecules which can form a heterotetramer.
In erythrocytes what affects the lateral motility of membrane proteins?
Integral proteins to the cytoskeleton.
What is a haemolytic anaemia?
These are caused by mutations, affecting the cytoskeleton of erythrocytes. The cells change shape and are therefore cleared by the spleen.
What disorder is a result of 50% loss of spectrin in erythrocytes?
Hereditary spherocytosis. This means that the RBC are round and less resistant to lysis.
What is hereditary ellipocytosis?
This is when heterotetramers are not formed and this leads to rugby ball shaped cells which are fragile.
Describe the process of membrane protein synthesis.
This begins in the cytoplasm and is stopped by SRP until in contact with the membrane. (Signal is a group of hydrophobic amino acids). When in contact with membrane, translation continues until hydrophobic domain is in membrane - cannot be pushed through and so synthesis continues in the cytoplasm. The signal is cleaved. This process ensures correct positioning of the protein within the membrane.
How are multiple transmembrane domains folded into the membrane?
It is thought that the first is inserted into the membrane and then the rest are synthesised in pairs and then folded into the membrane.
When vesicles bud off, this can lead to inside out membrane. Why is this important?
This will tell us which substances the vesicles will interact with.
What are the roles of the membrane bilayer?
It is a highly selective barrier. It has roles in both communication and recognition.
