Lecture 4 Flashcards
(15 cards)
What evidence is there for proteins in membranes?
Function evidence
Ion gradients (transporters)
Specificity of cell responses (receptors)
Facilitated diffusion
Biochemical (seeing them)
Freeze fracture
Gel electrophoresis and membrane fractionation
How does freeze fracture work?
Frozen and break along fracture line. Separate into p and e face. Split bilayer and Use electron dense metal to highlight where proteins are and fill holes where they were.
What movements can proteins make in the bilayer?
Conformational change
Rotational
Lateral
No flip flop
Restrictions on membrane protein mobility?
Aggregates of proteins
Tethering to substrate or cytoskeleton
Interaction with other cells
Where do proteins tend to be found in the membrane?
Cholesterol poor areas as more fluidity
How to remove peripheral membrane proteins?
Changing ph or in ionic strength using salt for example.
How to remove integral membrane proteins?
Must use detergent to destroy bilayer
What can a hydro patchy plot be used for?
Used to see what sections of protein are hydrophilic and hydrophobic. Hydrophilic sections will be outside bilayer hydrophobic sections inside bilayer.
How do you anchor protein to bilayer?
Can use post translational lipid modification such as adding a fatty acid to constrain the structure in the bilayer
What is an erythrocytes cytoskeleton?
Spectrum forms an internal cage in the erythrocytes which is anchored to the membrane by attachment proteins such as ankyrin.
Give examples of two haemolytic anaemias.
Hereditary Spherocytosis where spectrin depleted and cells round and lose easily. Must replace every 120 days with blood transfusion.
Hereditary eliptocytosis where defect in spectrin results in cells taking rugby ball shape
How does secreted protein biosynthesis work?
Ribosome and sign all have srp attached which prevents translation. Srp recognised by docking protein and removed. Translation can then occur and protein is fed through membrane.
How does membrane protein biosynthesis work?
Srp is attached to signal and ribosome and prevents translation. Srp recognised by docking protein and is removed. Translation occurs through membrane until hydrophobic portion enters membrane this acts as a stop transfer ad locks protein in membrane.This docks protein in the membrane. Ribosome then leaves and continues to make protein intracellular lay. Results in intracellular and extracellular portion.
How do proteins associate with lipid bilayer?
Postranslational lipid modifications like fatty acid anchors.
Peripheral protein associations
What do signal peptidases do?
Cleave the SRP from the protein before translation is finished
