The Membrane Bilayer Flashcards
Give 5 functions of biological membranes
Highly selective permeability barrier , control of the enclosed chemical environment, communication, recognition- signalling molecules, signal generation in response to stimuli
What makes up the majority of the membrane?
Proteins
Membrane lipids are amphipathic, what is mean by this term?
They have hydrophilic and hydrophobic ends
What is a phospholipid made up of?
A hydrophilic phosphate head and a hydrophobic tail
What are glycolipids?
Sugar containing lipids
What are cerebrosides and gangliosides?
They are both glycolipids. Cerebrosides head group is a sugar monomer whereas gangliosides head group is an oligosaccharide
What is it called when the lipid bilayer forms a ring?
A liposome
What are the 4 ways a phospholipid can move?
Laterally (diffuse across same side of phospholipid bilayer), rotation around their own axis, flexion (tails wiggle) and flip flop (very rare phospholipids switch sides of the bilayer)
What is the influence of the cis double bond in bilayer structure?
It makes a kink meaning the phospholipids cant pack as tightly together.
Describe the structure of cholesterol
A polar head group, rigid planar steroid ring structure, non polar tail
How does cholesterol stabilise the membrane?
It reduces the effect of the external environment. At high temps it stabilises the membrane by raising its melting point and at low temps it intercalates between phospholipids and prevents them clustering together and stiffening
What is the evidence for proteins in membranes?
Facilitated diffusion
Ion gradients
Specificity of cell responses
What is an SDS page and how does it work?
It is a type of gel electrophoresis that separates proteins based on their Mr. The proteins are given a negative charge and the base of the gel is positively charged so the proteins move through the gel. The mesh only allows the smallest proteins to travel the furthest so the proteins separate out in the distance travelled along the gel by Mr
How does freeze fracture work?
Freeze sample to immobilise cell constitutes.
Push sharp knife against the frozen section and it will fracture between bilayers as the hydrophobic attraction between the two tails is the weakest part. The structure can then be viewed using an electron microscope
Biochemically how can we prove the presence of proteins in a membrane?
Cell fractionation and gel electrophoresis
Freeze fracture
What are the 3 types of motion provided to proteins in the membrane?
Conformational change
Rotation
Lateral
NOT flip flop as proteins eg receptors must be on the surface
What is the purpose of the cytoskeleton?
Maintains cell shape and protects integrity of membrane
What causes haemolytic anaemia?
When the cytoskeleton doesn’t form properly.
What is spherocytosis?
When spectrin is depleted , RBCs round up and are more likely to undergo lysis. Only treatment is regular blood transfusions
What is hereditary Elliptocytosis?
When the spectrin molecule is defective and RBCs look like rugby balls.
Describe the sequence of events that leads to a protein being secreted into the ER lumen
- SRP (signal recognition protein) binds to signal sequence on the ribosome in order to stop protein synthesis.
- Docking protein recognises SRP and delivers the ribosome to the signal sequence receptor.
- Protein synthesis continues into the ER
- The signal sequence is cut off by the enzyme signal peptidase
- Protein excreted into ER
- Ribosome moves back into the cytoplasm
How are intrinsic proteins secreted?
The protein will have a hydrophobic region which prefers to stay in the membrane so stops there. The protein synthesis continues forming a loop. Signal peptidases cut the protein so the non hydrophobic region is excreted into the ER and the hydrophobic region stays in the membrane and goes on to form intrinsic proteins
