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Membrane formation is due to the __nature of the molecules; polar heads favor contact with water, whereas their hydrocarbon tails interact with one another in preference to water
Molecules can arrange themselves in aqueous solutions by forming __>
polar heads favor contact with water, whereas their hydrocarbon tails interact with one another in preference to water
globular structures called micelle, in which the polar head groups form the outside surface of the micelle, which is surrounded by water, and the hydrocarbon tails are sequestered inside, interacting with one another
__, composed of two lipid sheets (bimolecular sheet)
The __ of each individual sheet do what,
forming a __ that acts as a __
The __ interact with the aqueous medium on each side of the bilayer
The two opposing sheets are called __
- Lipid bilayer
- hydrophobic tails
- interact with one another
- hydrophobic interior
- permeability barrier
- hydrophilic head groups
· The favored structure for most phospholipids and glycolipids in aqueous media is a __ rather than a __.
Two __ are too bulky to fit into the __.
In contrast, __ readily form micelles because they contain only one chain
- bimolecular sheet rather than a micelle
- fatty acid chains of a phospholipid or a glycolipid
- interior of a micelle
- salts of fatty acids
The formation of __instead of __by phospholipids is of critical biological importance
A micelle is a __, usually less than 200 angstroms in diameter. In contrast, a bimolecular sheet can __
- limited structure
- extend to macroscopic dimensions
Lipid bilayers form __= the structure of a bimolecular sheet is __
The growth of lipid bilayers is __ and __ in water
__ are the major driving force for the formation of lipid bilayers
__ are released from the __ of membrane lipids as what happens?
- spontaneously by a self-assembly process
- inherent in the structure of the constituent lipid molecules
rapid and spontaneous
- Hydrophobic interactions
- Water molecules
- hydrocarbon tails
- these tails become sequestered in the nonpolar interior of the bilayer
Also, __ between the hydrocarbon tails favor __.
Finally, there are __ between the __ and __
Thus, lipid bilayers are stabilized by __
Because lipid bilayers are held together by __ (predominantly hydrophobic), they are cooperative structures
- van der Waals attractive forces
- close packing of the tails
- electrostatic and hydrogen-bonding attractions
- polar head groups and water molecules
- the full array of forces that mediate molecular interactions in biological systems
- many reinforcing, noncovalent interactions
These hydrophobic interactions have three significant biological consequences:
- · Lipid bilayers have an inherent tendency to be extensive
- · Lipid bilayers will tend to close on themselves so that there are no edges with exposed hydrocarbon chains, and so they form compartments
- · Lipid bilayers are self-sealing because a hole in a bilayer is energetically unfavorable
__ can be formed from phospholipids
What are they? __
How are liposomes formed?
- Lipid vesicles
- They are aqueous compartments enclosed by a lipid bilayer and can deliver chemicals to cells
- Liposomes are formed by suspending a suitable lipid in an aqueous medium, and then sonicating to give a dispersion of closed vesicles that are quite uniform in size
Ions or molecules can be trapped in the __ of lipid vesicles how?
Ex: __ that form and can be separated from solution by dialysis or gel-filtration chromatography
The __of the bilayer membrane to glycine can be determined how?
- aqueous compartments
- by forming the vesicles in the presence of these substances
- glycine-containing vesicles
- by measuring the rate of efflux of glycine from the inner compartment of the vesicle to the ambient solution
__can be formed with __ embedded in them by __the proteins in the presence of __and then adding them to __from which __will be formed. __ provide valuable experimental tools for examining a range of membrane protein functions
__ can be injected into patients
- specific membrane proteins
- Protein-liposome complexes
- Liposomes containing drugs
A synthetic membrane is a __, which can be formed across a __.
Lipid bilayers are __ with the exception of water since it traverses such membranes
- planar bilayermembrane
- 1-mm hole in a partition between twoaqueous compartments by dipping a fine paintbrush into a membrane-formingsolution
- highly impermeable to ionsand most polar molecules
o The range of measured permeability coefficients is very wide
The permeability of small molecules is correlated with their __ relative to their __, suggesting that a small molecule might traverse a lipid bilayer membrane in the following way:
• First, it __, then it is __; and, finally, it does what?
- solubility in a nonpolar solvent
- solubility in water
- sheds its solvation shell of water
- dissolved in the hydrocarbon core ofthe membrane
- diffuses through this core to the other side of the membrane, where it becomes re-solvated in water
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