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BIOCH 200 (March 17, 2014) - Biological Membranes & Metabolism

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Walter Dixon

BIOCH 200 – End of Biological Membrane Lecture & Start of Metabolism Lecture (March 17, 2014) • Passive transport takes advantage of concentration gradient so it doesn’t take any energy or charge transfer. o *Porins and ion channels enable this via pore formation  *Porins characterized by β-barrels grouped together into a homotrimer • Relatively non-selective  *Ion channels are characterized by α-helices arranged in a homotetramer • Highly selective • *Active Transport transports molecules against their concentration gradient; requires energy o *Two types:  *Primary • *Energy source from ATP hydrolysis • *Direct Active Transport  *Secondary • *Energy source from established ion gradient that was created separately by ATP hydrolysis. • *Indirect Active Transport • Transporter proteins change conformation to transport molecules/ions o Aka “carrier proteins” o *Pore do not span entire membrane (only halfway and the half that the pore is in depends on its conformation) o *May be passive or active • Kinetics of passive transport o *The higher the concentration of substrate outside of the cell, the faster they will be brought into the cell (V)  *Max binding rate = V max  *[S] outside of cell need to reach V /2 = K max tr • *Gives us a control to compare rates of transport for different molecules because the concentration needed to reach V max is not really clear whereas, Vmax2 can be determined easily. • Types of transporter proteins: o *Uniport – only transports one type of molecule o *Symport – two different molecules are transported across membrane together (in the same direction)  *Ex. Na+/Glucose transporter; sodium ions are brought into the cell along with glucose molecules.  secondary active transport o *Antiport – two different molecules transported across membrane in opposing directions  *Usually, the two molecules are of the same charge to maintain membrane potential  *Ex. Na+/K+ ATPase
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