A Balancing Act Direct and Indirect Active Transport

A Balancing Act: Direct and Indirect Active Transport

The Basics n n The cell is the coolest thing ever. A cell is picky about its living conditions. Intracellular K+ ion concentration is maintained at 100 -150 m. M (35: 1 inside to outside ratio). Intracellular Na + ion concentration is maintained at 10 -15 m. M (0. 08: 1 inside to outside ratio).

Direct Active Transport: Sodium Potassium Pump n n 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 n n 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 n n n n 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 n 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.

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