A Balancing Act:
Direct and Indirect Active Transport
The Basics
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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
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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
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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
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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
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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.
QUESTIONS?