Cell Potassium Concentration and Anions

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Questions and Answers

What is the approximate concentration of potassium on the inside of the cell?

92 millimoles per liter

5 millimoles per liter

1000 millimoles per liter

150 millimoles per liter (correct)

What happens to the anions when potassium leaves the cell?

They become positively charged

They create a positive charge inside the cell

They are left behind, creating a negative charge (correct)

They leave the cell with the potassium

What is the purpose of the negative charge created by the anions?

To offset the concentration gradient of potassium (correct)

To repel potassium from the cell

To attract more potassium into the cell

To destroy the cell membrane

What is the magnitude of the negative charge that offsets the concentration gradient?

-92 Signup and view all the answers

What happens to the negative charge inside the cell when positive charge is injected?

It becomes less negative Signup and view all the answers

Why does potassium want to leave the cell?

Because of the concentration gradient Signup and view all the answers

What happens to the potassium that leaves the cell?

It comes back into the cell to be closer to the negative charge Signup and view all the answers

What is the result of the negative charge created by the anions on the potassium?

It attracts potassium to the cell Signup and view all the answers

What does Vm stand for in the context of cell membrane potential?

Membrane potential Signup and view all the answers

What is the formula for calculating the membrane potential of an ion?

The log of the concentration of the ion on the outside over the concentration on the inside Signup and view all the answers

What is the membrane potential of potassium?

-92 millivolts Signup and view all the answers

How does the charge of an ion affect the formula for membrane potential?

The charge of the ion is multiplied by the formula Signup and view all the answers

What is the direction of movement of sodium ions across the cell membrane?

Into the cell Signup and view all the answers

What is the membrane potential of chloride?

-86 millivolts Signup and view all the answers

What is the membrane potential of calcium?

+123 millivolts Signup and view all the answers

What is the direction of movement of potassium ions across the cell membrane?

Out of the cell Signup and view all the answers

What happens to the potassium ions when the membrane potential changes from -92mV to -46mV?

They leave the cell at an increased rate. Signup and view all the answers

What is required for a membrane potential to form?

A concentration gradient and permeability to one ion. Signup and view all the answers

What would happen to the membrane potential if the cell were permeable to two ions?

The membrane potential would become less negative. Signup and view all the answers

What is the equilibrium point for the membrane potential in this scenario?

-92mV Signup and view all the answers

What is the purpose of the concentration gradient in this scenario?

To give potassium a desire to leave the cell. Signup and view all the answers

What does permeability refer to in this scenario?

The means by which potassium can leave the cell. Signup and view all the answers

What is the formula for membrane potential?

Vm = unknown formula Signup and view all the answers

What would happen to the membrane potential if the concentration gradient were reversed?

The membrane potential would become positive. Signup and view all the answers

How many ions must the cell be permeable to in order to form a membrane potential?

Only one ion Signup and view all the answers

Why does the membrane potential slide back down to -92mV after being changed to -46mV?

Because of all of the above. Signup and view all the answers

Study Notes

Potassium Ions and Concentration Gradients

Inside a cell, there is a higher concentration of potassium (around 150 millimoles per liter) compared to outside the cell (around five millimoles per liter).
Due to the concentration gradient, potassium ions leave the cell, leaving behind anions that create a negative charge.
The negative charge attracts potassium ions back into the cell.

Membrane Potential

The negative charge created by the anions is around -92 millivolts, which offsets the concentration gradient.
If a positive charge is introduced into the cell, it reduces the negative charge, making the membrane potential less negative.
As potassium ions continue to leave the cell, the anions left behind contribute to the negative charge, causing the membrane potential to return to -92 millivolts.

Thought Experiment

If a cell is only permeable to potassium ions, adding a positive charge or changing the concentration gradient does not affect the membrane potential, which will always return to -92 millivolts.
Two important conditions are required for this: a concentration gradient and permeability to only potassium ions.

Diagram Explanation

Four scenarios are possible: no concentration gradient and no permeability, concentration gradient but no permeability, permeability but no concentration gradient, and both concentration gradient and permeability.
A membrane potential is only possible when there is both a concentration gradient and permeability to potassium ions.

Formula for Membrane Potential

The formula for membrane potential (Vm) is Vm = 61.5 x log([K_out] / [K_in]), where [K_out] and [K_in] are the concentrations of potassium outside and inside the cell, respectively.
The formula can be used to calculate the membrane potential for other ions, such as sodium, chloride, and calcium, by plugging in their respective concentrations.

Other Ions

Sodium has a membrane potential of +67 millivolts, chloride has a membrane potential of -86 millivolts, and calcium has a membrane potential of +123 millivolts.
Calcium has a two-plus charge, so the formula is adjusted to 30.75 instead of 61.5.

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Description

Recap of potassium concentration inside and outside cells, and its relation to anions. Understand the concept of concentration gradient and its effects.