M&R Session 1- Membrane Proteins, Assymetry And The Cytoskeleton Flashcards
What are the biochemical pieces of evidence for membrane proteins? (2)
Freeze fracture- the cell is frozen and then fractured using a knife. It will break at points of weakness, and proteins will be present in all fragments.
Membrane fractionation and gel electrophoresis
What are the functional pieces of evidence for membrane proteins? (3)
Facilitated diffusion
Ion gradients
Specificity of cell responses
What are the three mobilities of membrane proteins?
- lateral
- rotational
- conformational change
Which movement can membrane proteins not perform, and why?
Flip flop
Because membrane proteins have large hydrophilic moieties. The energy required to move these across the hydrophobic region of the bilayer would therefore be too great, and disturbance would also be too great.
What are the mobility restrictions of membrane proteins? (6)
- aggregate formation
- tethering
- interaction with other cells
- membrane-protein associations
- associations with peripheral proteins
- lipid-mediated effects- they separate into fluid phase and cholesterol poor regions.
How are peripheral proteins bound to the membrane surface?
By electrostatic and hydrogen bonds
How are peripheral proteins removed from the membrane surface?
By pH or ionic strength changes
What do integral proteins interact with?
The hydrophobic region of the bilayer
How are integral proteins removed from the bilayer?
Using detergents or organic solvents.
What is membrane protein asymmetry important for?
Function
What is different in the biosynthesis of normal proteins and membrane proteins?
Membrane proteins require spanning the membrane therefore this is done using stop-transfer signals which remain in the ER and allow protein synthesis to continue into the cytoplasm.
What forms the erythrocyte cytoskeleton?
Peripheral proteins.
What is the composition of the erythrocyte cytoskeleton?
Spectrin and actin form a complex which is bound to the membrane using two molecules: ankyrin and glycophorin A, which themselves are bound to band 3 and band 4.1 respectively.
What is the erythrocyte cytoskeleton important for?
Maintaining the structure and shape of RBCs.
What is hereditary spherocytosis?
When 40-50% of spectrin is depleted; RBCs round up and lyse more easily, shortening their lifespan. The bone marrow is unable to compensate for this and therefore haemolytic anaemia results.
