Cell Biology Study Guide: Membrane Potential and Neuronal Function

Q1. Describe the permeability of a cell membrane to ions. Describe different mechanisms by which ions can be transported across cell membranes. Do they all require energy?

Background

Topic: Membrane Permeability and Ion Transport

This question tests your understanding of how cell membranes regulate ion movement and the various transport mechanisms involved, including whether these processes require energy.

Key Terms and Concepts:

• Permeability: The ability of the membrane to allow substances to pass through.

• Passive Transport: Movement of ions without energy input (e.g., diffusion, facilitated diffusion).

• Active Transport: Movement of ions against their concentration gradient, requiring energy (e.g., pumps).

• Ion Channels: Proteins that allow specific ions to pass through the membrane.

• Carrier Proteins: Transport proteins that move ions across membranes.

Step-by-Step Guidance

1. Start by explaining that the lipid bilayer of the cell membrane is generally impermeable to charged ions, so specialized proteins are needed for ion transport.

2. Identify the main mechanisms for ion transport: passive diffusion through channels, facilitated diffusion via carrier proteins, and active transport using pumps.

3. Discuss which mechanisms require energy (ATP) and which do not. Passive transport does not require energy, while active transport does.

4. Consider examples of each mechanism, such as sodium-potassium pumps (active) and potassium channels (passive).

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Q2. What does the term “membrane potential” mean? How is it measured? What 2 components make up the membrane potential? What type of potential do those 2 components combine into?

Background

Topic: Membrane Potential

This question is about the electrical properties of cell membranes, how membrane potential is defined and measured, and the factors that contribute to it.

Key Terms and Concepts:

• Membrane Potential: The voltage difference across a cell membrane.

• Electrochemical Gradient: Combination of electrical and chemical gradients.

• Resting Potential: The baseline membrane potential when the cell is not active.

• Measurement: Typically done using microelectrodes.

Step-by-Step Guidance

1. Define membrane potential as the difference in electrical charge across the cell membrane.

2. Explain how membrane potential is measured, usually with microelectrodes inserted into the cell.

3. Identify the two main components: the concentration gradient of ions and the electrical gradient.

4. Discuss how these combine to form the electrochemical gradient, which determines the overall membrane potential.

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Q3. What is the value in millivolts of a typical “resting membrane potential”?

Background

Topic: Resting Membrane Potential

This question tests your knowledge of the typical voltage across the membrane of a resting cell.

Key Terms:

• Resting Membrane Potential: The steady-state voltage across the membrane when the cell is not firing.

• Millivolts (mV): Unit of measurement for membrane potential.

Step-by-Step Guidance

1. Recall that the resting membrane potential is usually negative relative to the outside of the cell.

2. Think about the typical range for most animal cells, especially neurons.

3. Consider what factors (ion concentrations, permeability) contribute to this value.

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Q4. What type of pump establishes and maintains the resting membrane potential? What is the energy source for this pump? How much energy is used in a typical cell for this? How much energy in a neuron?

Background

Topic: Sodium-Potassium Pump and Cellular Energy

This question focuses on the role of the Na+/K+ pump in maintaining membrane potential and the energy requirements for its function.

Key Terms and Formulas:

• Na+/K+ Pump (Sodium-Potassium ATPase): Active transport protein.

• ATP: Adenosine triphosphate, the energy source.

• Energy Consumption: Fraction of cellular ATP used for pump activity.

Step-by-Step Guidance

1. Identify the pump responsible for maintaining resting membrane potential (Na+/K+ ATPase).

2. Explain that this pump uses ATP to move sodium and potassium ions against their gradients.

3. Discuss the proportion of cellular energy used for this process in typical cells and neurons.

4. Consider why neurons might use more energy for this pump compared to other cells.

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Q5. Trace the steps involved in one cycle of a Na+/K+ pump. How much ATP is used per cycle? What is the effect of one cycle on resting membrane potential?

Background

Topic: Sodium-Potassium Pump Mechanism

This question tests your understanding of the molecular steps in the Na+/K+ pump cycle and its impact on membrane potential.

Key Terms and Concepts:

• Na+/K+ Pump: Moves 3 Na+ out and 2 K+ in per cycle.

• ATP Hydrolysis: Provides energy for the pump.

• Electrogenic Effect: Net movement of charge affects membrane potential.

Step-by-Step Guidance

1. Describe the sequence: binding of Na+ ions, ATP hydrolysis, conformational change, release of Na+, binding of K+, return to original state, release of K+.

2. State how many ATP molecules are used per cycle.

3. Explain the net effect on membrane potential (more positive charge moved out than in).

4. Consider how this contributes to the overall negative resting membrane potential.

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Q6. Describe different types of gated ion channels. What are 3 different triggering events that result in the opening of these ion channels? What are the possible effects on membrane potential when these channels are open?

Background

Topic: Gated Ion Channels and Membrane Potential

This question is about the types of ion channels, their activation mechanisms, and their effects on membrane potential.

Key Terms:

• Gated Ion Channels: Channels that open in response to specific stimuli.

• Voltage-Gated, Ligand-Gated, Mechanically-Gated: Types of channels.

• Depolarization, Hyperpolarization: Effects on membrane potential.

Step-by-Step Guidance

1. List the main types of gated ion channels (voltage, ligand, mechanical).

2. Describe three triggering events: change in voltage, binding of a molecule, physical deformation.

3. Explain how opening these channels can change the membrane potential (e.g., influx of Na+ causes depolarization).

4. Consider the possible outcomes depending on which ions move and in which direction.

Try solving on your own before revealing the answer!