1.2 Membrane Proteins Flashcards
Describe the process of SDS-PAGE
Cells are burst so all the cell components are released. The contents are spun to create a pellet. The pellet can then be separated via gel electrophoresis.
Why are proteins important in the cell membrane? (3)
Facilitated diffusion
Creating ion gradients
Specificity of cell responses
Describe the Freeze Fracture technique
A vesicle is frozen in ice. It is then cut with a fine knife. The vesicle splits along the lines of weakness. This results in a P fracture face and an E fracture face so the structure of the membrane can be seen.
List the 3 ways a protein can move
Laterally
Rotation
Conformational change
When will a protein’s mobility be reduced?
When it becomes an aggregate (attaches to a substate)
When will a protein become fixed?
When it becomes tethered (attaches to a basement membrane)
When it interacts with other cells
Describe a peripheral protein. Can they be removed?
A peripheral protein is a protein bound to the surface of a membrane by electrostatic and hydrogen bond interactions. They can be removed by changes in pH or in ionic strength.
Describe an integral protein. Can they be removed?
An integral protein interacts exclusively with hydrophobic domains of the lipid bilayer. They can only be removed by agents that compete for non-polar interactions.
Describe the structure of a transmembrane polypeptide
Approximately 18-22 amino acids span the membrane in an alpha-helix conformation. The amino acids must be small, hydrophobic, polar or uncharged.
What does a hydropathy plot show?
The areas of a protein that are hydrophobic and hydrophilic
The areas of the protein that are the transmembrane domains
Explain the process of membrane topology
Ribosomes attach to the mRNA chains to start translation.
A hydrophobic signal sequence will halt translation.
An SRP (signal receptor protein) will bind to the signal area.
The SRP moves the protein to the target cell and then binds to the docking station to open the sequence receptor.
The protein then moves into the lumen of the cell and the signal sequence is cleaved by signal peptidases.
Hydrophobic amino acid chains stick in the membrane.
The N-terminal faces the lumen.
Explain what happens when there are multiple transmembane domains
The subsequent domains are made in the cytoplasm and brought back into the membrane by heat-shock proteins. Eg. a G-protein coupled receptor
Explain why people suffer from Hereditary Spherocytosis
An allele for the protein, spectrin, is not present. The levels are decreased by 50% and so a weaker cytoskeleton around erythrocytes forms. The RBCs are more likely to die and so leads to anaemia.
Explain why people suffer from Hereditary Elliptocytosis
There is a defect in the spectrin molecule so they are unable to form heterotetramers. This causes fragile RBCs which results in anaemia.
