-passive transport, no conformational change.
-Form of passive transport
-involves proteins, but no energy.
-molecules pass base on concentration or electrical gradients.
-They are selective
-Bind molecule, undergo conformational change that releases molecule on other side of the membrane.
-Rate is saturatable because it is mediated by a protein.
-Due to conformational change, rate is slower than channel
-Powered by the electrochemical gradient,
-direct is reversible
-slowest due to hydrolyzing of ATP, active transport, conformational change following transport
1. Uniport-transport of single molecule, driven entirely by concentration gradient
2. Symport-transports two molecules in same direction
3. Antiport- transports two molecules in opposite directions
-For all three, transport is saturatable, reversible & driven entirely by EC gradient.
-Passive Transport is saturatable, simple diffusion is not
-Electrochemical gradient of ion across cell membrane provides energy to drive transport of other molecule into cell against its concentration gradient.
-Done by transporters (symporter)
-initial gradient established by active transport
1. Voltage Gated-change in membrane voltage opens gate
2.Ligand-gated (extracellular ligand)-ligand opens gate
3. Ligand-gated (intracellular ligand)-ligand opens gate
4. Mechanically Gated-stretching or membrane opens gate
-Let ions move passively across the membrane driven by their electrochemical gradient.
-They are selective
-Conduction is turned on & off by opening & closing a gate. This can be regulated by an external stimulus such as ligand binding or membrane voltage.
-Due to the necessity of hydrolyzing ATP, pumps are the slowest transport proteins.
-P-type pump- phosphorylated during the hydrolysis of ATP to pump ions such at Na+ or H+ out of the cell
-F-type (and V-type) proton pump- harness the energy of protons flowing down their concentration gradient to produce ATP in mitochondria
-ABC transporter- pump small molecules using the energy of ATP hydrolysis
• 3 Na+ ions bind a site on the pump initially exposed to cytosol.
• Na+-binding causes ATP hydrolysis & this transfers a PO4 to aspartate
• Adding PO4 to Asp changes the pump’s structure; this exposes the Na+ & K+ binding sites to the e.c. space where Na+ is released & where 2 K+ ions bind the pump.
• K+-binding causes release of the PO4 from the pump & this changes the structure to expose the K+ binding sites to cytosol where K+ is released & where 3 new Na+ ions bind to the pump.
-Atypical ABC transporter
-Cl- channel that is activated by phosphorylation
-flow of Cl- is dependent on the electrochemical gradient, not ATP hydrolysis.
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