Chapter 11 Flashcards
Micelle
An aggregate of amphipathic molecules in water, with the nonpolar portions in the interior and the polar portions at the exterior surface, exposed to water.
Bilayer
A double layer of oriented amphipathic lipid molecules, forming the basic structure of biological membranes. The hydrocarbon tails face inward to form a continuous nonpolar phase.
Vesicle
A small, spherical, membrane-bounded particle with an internal aqueous compartment that contains components such as hormones or neurotransmitters to be moved within or out of a cell.
Fluid mosaic model
The model describing biological membranes as a fluid lipid bilayer with embedded proteins; the bilayer exhibits both structural and functional asymmetry.
Lipid transfer protein
A family of proteins that transfer membrane lipids between parts of the endomembrane system at contact points.
Integral proteins
Proteins firmly bound to a membrane by interactions resulting from the hydrophobic effect; as distinct from peripheral proteins.
Peripheral proteins
Proteins loosely bound to a membrane by hydrogen bonds or electrostatic forces; generally water-soluble once released from the membrane. Compare integral proteins.
Amphitropic protein
Proteins that associate reversibly with the membrane and thus can be found in the cytosol, in the membrane, or in both places.
Monotopic
integral proteins have small hydrophobic domains that interact with only a single leaflet of the membrane
Bitopic
proteins span the bilayer once, extending on either surface.
Polytopic
proteins cross the membrane several times.
Hydropathy index
- free energy of transfer
- ranges from highly exergonic for charged or polar residues to highly endergonic for amino acids with aromatic or aliphatic hydrocarbon side chains.
B barrel
Another structural motif common in bacterial and mitochondrial membrane proteins is the barrel, in which 20 or more transmembrane segments form sheets that line a cylinder
Porins
proteins that allow certain polar solutes to cross the outer membrane of gram-negative bacteria such as E. coli, have many-stranded barrels lining the polar transmembrane passage
Positive-inside rule
The general observation that most plasma membrane proteins are oriented so that most of their positively charged residues (Lys and Arg) are on the cytosolic face.
GPI-anchored protein
A protein held to the outer monolayer of the plasma membrane by its covalent attachment through a short oligosaccharide chain to a phosphatidylinositol molecule in the membrane.
Flippases:
Membrane proteins in the ABC transporter family that catalyze movement of phospholipids from the extracellular leaflet (monolayer) to the cytosolic leaflet of a membrane bilayer.
Floppases
Membrane proteins in the ABC transporter family that catalyze movement of phospholipids from the cytosolic leaflet (monolayer) to the extracellular leaflet of a membrane bilayer.
Scramblases
are proteins that move any membrane phospholipid across the bilayer down its concentration gradient (from the leaflet where it has a higher concentration to the leaflet where it has a lower concentration); their activity is not dependent on ATP, although some require Ca2+
FRAP (fluorescence recovery after photobleaching)
A technique used to quantify the diffusion of membrane components (lipids or proteins) in the plane of the bilayer.
Microdomains
cholesterol-sphingolipid microdomains of the plasma membrane make the bilayer slightly thicker and more ordered (less fluid) than neighboring regions, which are rich in phospholipids.
- microdomains are more difficult to dissolve with nonionic detergents; they behave like liquid-ordered sphingolipid ra s adri on an ocean of liquid-disordered phospholipids
Rafts
adri ft on an ocean of liquid-disordered phospholipids
Caveolin
an integral protein with two globular domains connected by a hairpin-shaped hydrophobic domain that binds the protein to the cytoplasmic leaflet of the plasma membrane