Electrochemical gradients and secondary active transport | Khan Academy

Summary

This video explains the function of the sodium-potassium pump in establishing a cell's resting membrane potential by actively transporting sodium and potassium ions. It highlights how the electrochemical gradient created by the pump influences ion diffusion, balancing concentration and charge effects. The video also introduces the concept of secondary active transport through a sodium-glucose symporter, which utilizes the energy from sodium ions moving down their gradient to help glucose enter the cell against its concentration gradient. This interplay of gradients and transport mechanisms is essential for cellular function.

Takeaways

• 🔄 The sodium-potassium pump actively transports three sodium ions out of the cell for every two potassium ions it pumps in.
• ⚖️ The ratio of sodium to potassium transport does not fully establish the resting membrane potential on its own.
• 🌊 Potassium ions begin to diffuse out of the cell down their concentration gradient, but their positive charge creates a balancing force that limits this movement.
• 🔋 The electrochemical gradient is a combination of the concentration gradient and the electric potential difference across the membrane.
• ⚡ Positively charged sodium ions tend to diffuse into the cell due to their concentration gradient and the positive charge outside.
• 🌀 The electrochemical gradient serves as a source of potential energy for the cell.
• 🔗 Symporters utilize the electrochemical gradient of sodium to transport other molecules against their concentration gradient.
• 🍬 The sodium-glucose symporter co-transports sodium ions and glucose into the cell, using the sodium gradient as energy.
• 📈 Secondary active transport is the process where energy from one gradient (sodium) is used to drive the transport of another molecule (glucose) against its gradient.
• 💡 Understanding these transport mechanisms is essential for grasping how cells maintain homeostasis and manage nutrient uptake.

Q & A

What is the primary function of the sodium-potassium pump?

The sodium-potassium pump primarily helps a cell establish its resting membrane potential by actively transporting three sodium ions out of the cell and two potassium ions into the cell.

How does the sodium-potassium pump affect the concentration gradients of sodium and potassium ions?

The pump creates a higher concentration of sodium ions outside the cell and a higher concentration of potassium ions inside the cell, which is crucial for maintaining the resting membrane potential.

What role do potassium ions play in establishing the resting membrane potential?

Potassium ions diffuse down their concentration gradient from the inside to the outside of the cell, but their movement is influenced by the charge difference across the membrane, preventing equal concentrations.

What is an electrochemical gradient?

An electrochemical gradient is the combined effect of the concentration gradient and the electric gradient acting on an ion, which determines the direction and movement of that ion across the membrane.

How do sodium ions contribute to the electrochemical gradient?

Sodium ions are concentrated outside the cell and are attracted to the inside due to both the concentration gradient and the positive charge outside the cell, creating a strong electrochemical gradient.

What is a symporter, and how does it function in the context of sodium ions?

A symporter is a protein that utilizes the energy from the electrochemical gradient of sodium ions to transport other molecules, such as glucose, into the cell against their concentration gradient.

What is Secondary Active Transport?

Secondary Active Transport refers to the process where the energy stored in the electrochemical gradient of one molecule, like sodium, is used to drive the transport of another molecule, like glucose, against its own concentration gradient.

Why is glucose transported against its concentration gradient?

Glucose is transported against its concentration gradient to ensure the cell can uptake as much glucose as possible for energy and metabolic needs, even when its concentration is low inside the cell.

What would happen if the sodium-potassium pump were inactive?

If the sodium-potassium pump were inactive, sodium ions would accumulate inside the cell and potassium ions would leak out, disrupting the resting membrane potential and potentially leading to cell dysfunction.

How does the concept of potential energy relate to the electrochemical gradient?

The electrochemical gradient represents potential energy for ions, as it creates a driving force for ions to move across the membrane, similar to how water flows down a waterfall, allowing cells to harness this energy for various transport processes.