Question

How many pore-forming \(K^{+}\)channel subunits assemble to form a functional channel? a. One b. Two c. Four d. None of the above

Short answer

Answer: Four subunits.

Step-by-step solution

Brief background knowledge on potassium ion channels

Potassium ion (K+) channels are membrane proteins that allow the selective passage of potassium ions across the cellular membrane. These channels are important for maintaining the resting membrane potential and controlling the electrical excitability of cells.

Analyze the options

Potassium ion channels are formed by the assembly of multiple protein subunits. Let's consider each option individually: a. One subunit b. Two subunits c. Four subunits

Determine the number of subunits needed

In a functional potassium ion channel, the channel pore is formed by the assembly of four subunits. Each subunit contributes to creating the ion-selective pore. Four subunits together form a central pore in which potassium ions can pass through, and this is the minimum requirement for a properly functioning potassium ion channel.

Choose the correct answer

Based on the facts mentioned above, the correct answer is: c. Four subunits (required to form a functional potassium ion channel)

Key concepts

Membrane Proteins

Membrane proteins play a vital role in the functioning of cells. They are embedded in the cell's lipid bilayer and serve several functions. One of their key functions is to form channels or pores for molecules to traverse the otherwise impermeable cell membrane.

The potassium ion ( K^+ ) channel is a perfect example of such a protein. These channels allow specific ions to pass through, maintaining cellular homeostasis. Ion selectivity is a crucial attribute and comes from the precise structure provided by the channel's protein subunits.

Potassium channels are comprised of multiple subunits, typically four, that form a pore. This unique assembly enables them to manage the movement of potassium ions across the cell membrane effectively. This selective permeability contributes to various physiological processes, including nerve signal transmission and muscle contraction.

Electrical Excitability

Electrical excitability refers to the ability of cells, especially nerve and muscle cells, to generate rapid responses to stimuli. This is primarily governed by ion channels embedded in the cell membrane.

The opening and closing of these channels in response to changes in voltage or other signals is what allows cells to transmit electrical signals quickly. Potassium ion channels, for example, open and close to modulate the flow of potassium ions, playing a significant role in generating electrical signals.

• They help reset the electrical state of the cell after a nerve impulse is transmitted.
• They contribute to the 'repolarizing' phase of an action potential by allowing potassium ions to exit the cell.

Electrical excitability is fundamental to many physiological processes, enabling the rapid transmission of signals across the nervous system.

Resting Membrane Potential

Resting membrane potential is the electrical charge difference across the cell membrane when a cell is not transmitting a signal. This is an essential aspect of a cell's electrical activity, especially crucial in nerve and muscle cells.

The resting membrane potential is primarily maintained by the distribution of ions on either side of the cell membrane, mainly due to the action of ion channels. Potassium ion channels, in particular, contribute significantly to this potential.

• The inside of the cell is typically negative relative to the outside, around -70mV in neurons.
• This potential is mainly due to the higher permeability of potassium ions compared to other ions at rest.
• Potassium channels allow the slow leak of potassium ions out of the cell, maintaining the negative charge inside.

Maintaining a stable resting membrane potential is crucial for the cell's readiness to respond to incoming stimuli and initiate an action potential, a primary signal in excitable cells.