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concentration gradients (used in secondary active transport)Exhibit a maximum level like carrier-mediated facilitated diffusion1.Primary active transport Energy derived from ATP, changes shape of carrier protein which pumps substance across plasma membrane against concentration gradient, 40% of ATP is expended Most prevalent is sodium-potassium pump because part of it acts as ATPase – it must work non-stop to keep K+ and Na+ from leaking down their concentration gradients, the pump helps maintain normal tonicity on each side of the plasma membrane ensuring the cells never shrink or explode due to osmosis, it works in these stepsi.Thee Na+ in cytosol binds to the pump protein ii.Binding of Na+ triggers hydrolysis of ATP into ADP which attaches a phosphate group to the pump protein changingits shape and expelling the three Na+ into the extracellular fluid, now the shape favors binding to two K+iii.The binding of the K+ triggers release of the phosphate group again changing the shape of the pump protein againiv.As the pump protein reverts to its original shape it releases the K+ into the cytosol and is read to bind to the Na+ again 2.Secondary Active Transport Energy stored in a Na+ or H+ concentration gradient is used to drive other substances across the membrane against their own concentration gradients, these gradients are established by primary transport and thus secondary active transport indirectly uses energy obtained from the hydrolysis of ATP (the steep concentration gradient of Na+ results in storage of potential energy, and when there is a leak for Na+ to come back in this energy is converted to kinetic energy and is used to transport other substances). Secondary active transport harnesses the energy of other cells by providing routes for Na+ to leak through into cells – the carrier protein binds to both Na+ and the other substance changing shape so that they both may enter the cell -Symporters move substances in the same direction, antiporters move two substances in opposite directions 3.Vesicle TransportA vesicle is a small, spherical sac that transport a variety of substance across the membrane and import materials from and release materials into extracellular fluid Endocytosis process in which material move into a cell in a vesicle formed from the plasma membrane
-three types: i.receptor-mediated endocytosis – a highly selective type in which cells take up specific ligands (molecules that bind to specific receptors). The vesicle is formed after a receptor protein recognized and binds to a particular particlein the extracellular fluid. The process of endocytosis of LDL’s is as follows:a.binding LDL particle binds to specific receptor (integral potein located in the clathrin-coated pits) to form a receptor-LDL complex, here the protein clathrin attaches to the membrane on its cytoplasmic end, many clathrinmolecules come together forming a basketlike structure around the complexes causing the membrane to invaginate or fold inwardb.vesicle formation