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Sodium-Potassium Pump Cycle

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About This MicroSim

This interactive diagram illustrates the Na⁺/K⁺-ATPase (sodium-potassium pump), a transmembrane protein that uses ATP hydrolysis to transport 3 Na⁺ ions out of the cell and 2 K⁺ ions into the cell per cycle. The diagram shows the pump embedded in the phospholipid bilayer with the concentration gradients it maintains.

Use Explore mode to hover over each structure and learn about its role in active transport. Switch to Quiz mode to test your knowledge of pump components and ion gradients.

How to Use

  1. Explore mode — Hover over any numbered marker or label to see a description of that structure and its AP exam relevance
  2. Quiz mode — A structure name appears in the prompt; click the correct marker on the diagram to identify it
  3. After completing the quiz, try again to improve your score

Key Structures

Pump Protein and Binding Sites

  • Na⁺/K⁺-ATPase Pump Protein — the large transmembrane protein that undergoes E1/E2 conformational changes
  • Na⁺ Binding Sites — three high-affinity sites on the cytoplasmic face (E1 conformation)
  • K⁺ Binding Sites — two high-affinity sites on the extracellular face (E2 conformation)
  • ATP Binding Site — cytoplasmic domain where ATP hydrolysis and autophosphorylation occur

Ion Gradients

  • Na⁺ Ions — high concentration outside (~145 mM), low inside (~12 mM)
  • K⁺ Ions — high concentration inside (~140 mM), low outside (~5 mM)
  • Electrochemical Gradient — the combined chemical and electrical gradient that stores potential energy

Energy Molecules

  • ATP — energy source hydrolyzed to power the pump cycle
  • ADP + Pᵢ — products released after phosphorylation drives the conformational change

Pump Cycle Summary

Step Conformation Event
1 E1 (open to cytoplasm) 3 Na⁺ bind from cytoplasm
2 E1 → E1-P ATP hydrolysis phosphorylates pump
3 E1-P → E2-P (open to outside) 3 Na⁺ released extracellularly; 2 K⁺ bind
4 E2-P → E1 Dephosphorylation; 2 K⁺ released to cytoplasm

Lesson Plan

Grade Level

9-12 (AP Biology)

Duration

10-15 minutes

Prerequisites

  • Plasma membrane structure (phospholipid bilayer)
  • Passive vs. active transport
  • ATP structure and hydrolysis

Activities

  1. Exploration (5 min): Use Explore mode to identify all 12 structures and read descriptions
  2. Guided Practice (5 min): Complete the Quiz mode, focusing on distinguishing Na⁺ from K⁺ binding sites and understanding the E1/E2 conformational cycle
  3. Assessment (5 min): Answer reflection questions connecting the pump to resting membrane potential and secondary active transport

Assessment

  • Can students explain why the pump is electrogenic (3 Na⁺ out vs. 2 K⁺ in)?
  • Can students distinguish primary from secondary active transport?
  • Can students predict what happens to a cell if the pump is inhibited (e.g., by ouabain)?

References

  1. Sodium-potassium pump — Wikipedia
  2. Active Transport — AP Biology, College Board
  3. Alberts et al. Molecular Biology of the Cell, 6th ed. — Chapter 11: Membrane Transport