Three types of lipid motions
Lateral diffusion
Rotation
Flexion
Rare: flip flop
How do membrane proteins associate with lipid bilayers
- Transmembrane
- Membrane associated
- Lipid linked
- Protein attached
1-3 integral, 4 peripheral
Process of phospholipid after synthesis from ER
- Membrane asymmetry is established during synthesis in the ER
- scramblases flip phospholipids from one face to the other in ER
- Flippases move specific phospholipids from extracellular face in golgi. Flop ashes move the phospholipids in the opposite direction.
- Membrane assembled at ER is exported by vesicle budding. Cytosolic face at ER remains the cytosolic face.
Phospholipid enzymes
Scramblases: flip phospholipids to a different side
Flippases: move phospholipids from outside layer to the inside
Flopases: Move phospholipids from inside layer to outside
Membrane associates carbohydrates
Protect the cell from chemical and mechanical damage
Lubrication
Cell-cell recognition
Composed of:
Glycoproteins, proteoglycan, glycolipid
Chemical composition of membranes
Composition includes
Lipids (phospholipids and cholesterol)
Proteins
Carbohydrate groups
How do cells restrict the movement of membrane proteins
The association with the cytoskeleton. Such as being bound.
How does the amino acid composition on the surface of a protein determine whether it is an integral proteins
If the alpha helix contains many nonpolar amino acids, it can span a membrane bilayer
The hydrophobic polypeptide backbone (stabilized by H bonds) is shielded from hydrophobic lipid hydrocarbons.
How do detergent molecules “breakup” lipid vesicles
Detergents separate integral proteins from lipid bilayer
- They disrupt hydrophobic associations
- a membrane protein can be combined with a detergent Michelle. The product of this is a water-soluble complexes of transmembrane protein and detergent + water soluble mixed lipid detergent micelles.
How can integral membranes be removed from membrane?
Removed by detergents.
Properties of detergents
Amphipathic
Single hydrophobic chain
Do not form bilayers
Mono layer micelles
FRAP experiments
Fxcvc
Why can some proteins freely go through membranes
Uhouh
