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T domains
The ________, each built of six membrane- spanning helices, form the pathway through which the transported substance (substrate) crosses the membrane and determine the substrate specificity of each ABC protein.
Pure phospholipid bilayers
________ are essentially impermeable to water, but most cellular membranes contain water- channel proteins that facilitate the rapid movement of water in and out of cells.
ox helices
Each subunit contains six membrane- spanning ________ that form a central pore through which water moves.
CO2
The ________ diffuses out of the cell, and the OH- ions combine with intracellular protons, forming water.
passive diffusion
The first and rate- limiting step in transport by ________ is the movement of a molecule from the aqueous solution into the hydrophobic interior of the phospholipid bilayer, which resembles oil in its chemical properties.
multiple excitatory
A single neuron can be affected simultaneously by signals received at ________ and inhibitory synapses.
Sensitive electric measurements
________ suggest that the opening of a voltage- gated Na+ or K+ channel is accompanied by the movement of 10 to 12 protein- bound positive charges from the cytosolic to the axoplasmic surface of the membrane.
concentration gradient
Uniporters** transport a single type of molecule down its ________ via facilitated diffusion.
phospholipid bilayer
The** ________**, the basic structural unit of biomembranes, is essentially impermeable to most water- soluble molecules, ions, and water itself.
Transition
________ to the E2 conformation also generates two high- affinity K+ sites accessible to the ectoplasmic face.
free energy
To calculate the ________ change △G corresponding to the transport of an ion across a membrane, consider the independent contributions from each of the forces to the** electrochemical gradient**
amino acids
Glucose and ________** cross the plasma membrane into most mammalian cells with the aid of uniporters.
none
Some proteins are synthesized in dendrites, but ________ are made in** axons or axon terminals**
electrochemical gradient
The proton ________ across the plant vacuole membrane is used in much the same way as the Na+ ________ across the animal- cell plasma membrane.
Myelination
relative diffusion rate
The ________ of any substance across a pure phospholipid bilayer is proportional to its concentration gradient across the layer and to its hydrophobicity and size.
