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Membrane Transport

Membrane Transport. Plant Physiology UNI. Two requirements. Route through the membrane Energy to move substances. Energy – 2 ways. Passive Energy already there (energy difference) Don’t need to add Active “Uphill” movement (energetically) Need to add energy

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Membrane Transport

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  1. Membrane Transport Plant Physiology UNI

  2. Two requirements • Route through the membrane • Energy to move substances Membrane Transport

  3. Energy – 2 ways • Passive • Energy already there (energy difference) • Don’t need to add • Active • “Uphill” movement (energetically) • Need to add energy • Direct or indirect addition of energy Membrane Transport

  4. Concentration isn’t everything • What makes transport “uphill?” • From lower energy to higher energy • Source of the energy depends on the solute • Uncharged solutes • Charged solutes Membrane Transport

  5. Energy for uncharged solutes • Example: sucrose • Difference in chemical activity is what counts • Proportional to concentration for solutes • So we usually just refer to concentration • Dots in diagrams = concentration for these Membrane Transport

  6. Energy for charged solutes • Example: K+, Cl- • Difference in electrochemical potential (ECP) is what counts • Includes differences in chemical energy (concentration) • Also includes electrical charge attraction • Dots on diagrams = ECP, not concentration Membrane Transport

  7. Uphill means… • From lower energy (ECP) to higher • Includes both sources of energy • Chemical (concentration-based) • Electrical • All cells use both to move solutes • All cells are charged (across membrane) Membrane Transport

  8. Active Transport #1: Pumps • Route: protein crossing membrane (uniport) • Binds ATP • Takes Pi off • ADP drifts away • Now can bind solute • Protein changes shape • Solute dropped off on other side of membrane • Pi drops off • Protein restored Membrane Transport

  9. AT #2: Cotransport • Route: protein symport • Carry two solutes together • In the same direction • Transport is needed “uphill” for one • The other provides energy (“downhill” for this) Membrane Transport

  10. Cotransport: Energy Energy from concentration (or ECP) difference will drive pink substance from top to bottom. Luckily there is another (green) substance here, whose energy (from concentration or ECP difference) will drive it from bottom to top. membrane But cell needs to move the pink substance from bottom to top. The pink “wants” to go down 2 units, but the green “wants” to go up 6 units (greater concentration difference for green). Membrane Transport

  11. Cotransport: Route A protein symport spans the membrane. The energy from the combined transport (pink = 2 down, and green = 6 up) gives a net force of 4 units pushing both substances through together. It can transport the green substance only if it also transports the pink substance. 4 units The symport will not operate unless both substrates are loaded. Then it will transport both of them in the same direction. Membrane Transport

  12. AT #3: Countertransport • Route: protein antiport • Carry two solutes together • In opposite directions • Transport is needed “uphill” for one • The other provides energy (“downhill” for this) Membrane Transport

  13. Countertransport: Energy Energy from concentration (or ECP) difference will drive blue substance from bottom to top. Luckily there is another (green) substance here, whose energy (from concentration or ECP difference) will drive it from bottom to top. membrane But cell needs to move the blue substance from top to bottom. The blue “wants” to go up 2 units, and the green “wants” to go up 6 units (greater concentration difference for green), but the transporter can only trade them. It can’t move both in the same direction. Membrane Transport

  14. Countertransport: Route A protein antiport spans the membrane. The energy from the combined transport (blue = 2 up, and green = 6 up) gives a net force of 4 units pushing both substances through together. It can transport the green substance only if it also transports the blue substance in the opposite direction. 4 units Blue “wants” to go up 2 units, and green “wants” to go up 6 units (greater concentration difference for green). Green wins, and transports blue the other way at the same time. Membrane Transport

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