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9 Cards in this Set
- Front
- Back
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1. What is carrier-mediated diffusion?
What is simple diffusion? |
Down a concentration gradient - transported binds a molecule, changes conformation, and releases the molecule on the other side of the membrane (saturable, hyperbolic kinetics)
Down a concentration gradient - molecule moves freely through a channel protein in membrane (non-saturable, linear kinetics) |
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2. How are the ion concentrations of Na+, K+, Ca2+. and Cl- across the cytoplasmic membrane?
How is the Na and K gradients created? |
Na: higher in extracellular fluid
K: higher in cytoplasm Ca: higher in ECF Cl: higher in ECF By an energy driven pump: Na+/K+ ATPase **All cells have the same Na+/K+ ATPase protein |
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3. What is the electrical gradient across the cytoplasmic membrane?
How is this charge gradient formed? What is the membrane potential |
Net positive charge outside membrane and net negative charge inside membrane
Diffusion of K ions down the K concentration gradient through K specific ion channels (maintenance K channel) Charge separation across the membrane creates an electrical potential across the membrane |
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5. When is the maintenance K channel open?
What does it all K ions to do? How do K ions want to diffuse? What do electrostatic repulsion do to them? How are these two forces balanced to achieve resting state? |
Open all the time
Reach a near-equilibrium distribution across the cytoplasmic membrane Want to diffuse down concentration gradient (out of the cell) Pushes them down the charge gradient (into the cell) Tiny fraction of K ions in the cell diffuse back out of the cell in order to balance these two forces and achieve K ion equilibrium across the membrane |
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6. For what are there specific ion channels for?
How are many ion channels similar? What is their structure? |
K, N, Ca, Cl, HCO3-, HPO4, and other ions
Have related AA sequence and similar 3-d structure Cluster of membrane spanning α-helices forming an opening or pore |
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7. How is ion selectivity conferred?
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By short segments of non-helical structure that form a constriction or bottleneck at one end of the pore
Variations in AA sequence determine size and electrical properties of pore and thus ion specificity |
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8. What are most ion channels?
In what conformation can they exist? How are most gated ion channels? |
Gated ion channels
Open or closed **like allosteric enzymes which assume either active or inactive conformation Closed and open only in response to specific stimuli |
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9. What do voltage gated ion channels open in response to?
What are voltage gated Na and K channels responsible for? What are voltage gated Ca channels responsible for? |
To electrical depolarization of cell memebrane
The rapid propagation of impulses along the surface membrane of nerve cells Release of NT and other secretory signals at nerve endings for muscular contraction and for other metabolic changes regulated by intracellular Ca in nerve and muscle cells |
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10. What do ligand gated ion channels open in response to?
Where can the ligand binding sites be? What are ligand gated Na channels responsible for? What do ligand gated Cl channels inhibit? |
Binding of specific molecules (ligands) by the channel protein
May be outside the cell or inside the cell Initiating nerve impulses at nerve synapses, in response to NT binding to sites outside the cell The initiation of nerve impulses at nerve synapses |
