Membranes - Biological Function - Membrane Proteins Flashcards
What are the evidences of Proteins in membranes?
- Functional involvement
- Facilitated diffusion
- ion gradients
- specificity of cell responses
- Biochemical procedures to examine membrane
- membrane fractionation + gel electrophoresis
- freeze fracture
What are the two fracture faces in freeze fracture?
- E fracture face (includes the outer membrane and some attached proteins)
- P fracture face (includes in inner membrane, some attached proteins and cytosol)
Where is the plane of fracture?
The weak spot of the phospholipi bilayer (in the midle)
How do proteins move in bilayers?
- conformational change
- rotational
- lateral diffusion
What are the restrictions of membrane protein mobility?
- aggregates
- tethering with substrates outside of cell or cytoskeleton in cell
- interaction with other cells through fixature of protein
- Cholesterol poor regions : proteins seperate out
How membrane proteins associate with lipid bilayer?
1. Peripheral
- Bound to surface
- electrostatic & H bond
2. Integral
- Interact extesnsively with hydrophobic domains
3. Lipid bpund protein
- very rare
- no function
How are peripheral proteins removed?
Changes in pH or ionic strength
How are integral proteins removed?
- detergents
- organic solvent
(agents that compete for non polar interactions)
What strutcture of protein is normally found in transmembrane domains and why?
a-helical : R groups are mostly hydrophobic
How are the hydrophobicity and hydrophilicity of protiens be analysed?
Hydropathy plots
List in order of size (from biggest to smallest), the type of proteins found in the erythrocyte membrane
*electrophoresis
- Spectrin a
- Spectrin B
- Band 3
- Glycophorin
- Band 4.1
- Actin
What are the integral and peripheral proteins of the erythrocyte membrane?
Integral
- Band 3
- Glycophorin A
Peripheral
- Ankyrin
- Spectrin
- Band 4.1
State the main feature and function of each protein in the erythrocyte membrane
Band 3 and Glycophorin A
Glycoprotein, hydrophilic
-prevent flip-flop and rotation
Ankyrin
adapter protein
- links spectrin to band 3
- restricts lateral mobility
Band 4.1
- links spectrin to glycophorin A
- restricts lateral mobility
Spectrin
Long, rod-like protein
forms heterotetremer
- shape and flexibity
What are the two types of haemolytic anaemias?
- Hereditary Spherocytosis
- Hereditary Elliptocytosis
What are the charactersitics of hereditary Spherocytosis
- Spectrin depleted by 40-50%
- Erythrocytes round up
- less resistant to lysis
- cleared by spleen
What are the characteristics of hereditary Elliptocytosis?
- Defect in spectrin molecule
- unable to form heterotetramers
- fragile elliptoid cells
How are membrane proteins inserted into ER membranes?
- Signal sequence recognised by SRP(signal recognition peptide)
- SRP binds to polypeptide chain - prevents further protein synthesis
- SRP recognised by receptor on the ER
- SRP released from signal sequence and signal sequence interact with SSR(signal sequence receptor)
- SSR found within Protein Translocator Complex
- Further protein synthesis through pore
- On membrane protein, stop transfer sequence forms transmembranal region
- Signal peptidase cleave signal sequence
How is correct orientation of membrane proteins maintained?
- internal signal sequence
- stop transfer sequence
- signal peptidase
