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A Balancing Act: Direct and Indirect Active Transport. The Basics. The cell is the coolest thing ever. A cell is picky about its living conditions. Intracellular K + ion concentration is maintained at 100-150 mM (35:1 inside to outside ratio).
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The Basics • The cell is the coolest thing ever. • A cell is picky about its living conditions. • Intracellular K+ ion concentration is maintained at 100-150 mM (35:1 inside to outside ratio). • Intracellular Na + ion concentration is maintained at 10-15 mM (0.08:1 inside to outside ratio).
Direct Active Transport:Sodium Potassium Pump • Pump is a transmembrane protein composed of two α and two β subunits. • Responsible for maintaining the sodium/potassium ion gradient. • Pump uses ATP for energy, therefore it is also known as Na+/K+ ATPase. • The sodium/potassium gradient is a key factor in nerve impulse transmission and protecting the cell from swelling.
Indirect Active Transport:Sodium/glucose Symporter • Facilitates movement of glucose into blood via sodium/glucose symporter protein. • Driven by uptake of sodium ions. • Occurs in epithelial cells that line the intestine. • Occurs when glucose concentration levels are lower than in the epithelial cells.
Steps of Na+/Glucose Symporter Cycle • Pump open to outside of cell. • Sodium ion bonds, leads to confirmation change. • Glucose binds, another confirmation change. • Pump opens to inside. • Sodium falls off. • Glucose falls off. • Pump returns to original state.
Conclusion • Cells use direct and indirect active transport to maintain its “picky” lifestyle. • Sodium potassium pump is an example of direct active transport. • Sodium/glucose symporter is an example of indirect active transport.
