PSL300 - Cell Membrane and Transport

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Questions and Answers

What characterizes simple diffusion across the cell membrane?

It is dependent on a concentration gradient. (correct)

It requires a specific carrier protein.

It is exclusive to water-soluble molecules.

It requires energy input from ATP.

Which statement best describes facilitated diffusion?

It involves carrier proteins assisting polar molecules. (correct)

It only occurs for lipid-soluble molecules.

It requires energy from ATP.

It can transport substances against their concentration gradient.

Which type of molecules can readily diffuse through the cell membrane?

Ions, without any assistance.

Lipid-soluble molecules. (correct)

Large polar molecules.

Organic anions, such as proteins.

What is the main factor determining the permeability of a molecule across the membrane?

Molecular size, lipid solubility, and charge. Signup and view all the answers

What role does the Na+/K+ pump play in maintaining membrane potential?

It creates an electrochemical gradient by moving ions across the membrane. Signup and view all the answers

During facilitated diffusion, what provides the energy for molecular movement?

The concentration gradient of the solute. Signup and view all the answers

Which of the following best describes the process of endocytosis?

Ingestion of external particles or fluids into the cell. Signup and view all the answers

What is the predominant characteristic of voltage-gated channels?

They open in response to changes in membrane potential. Signup and view all the answers

What type of transport moves molecules down their concentration gradient without requiring energy?

Facilitated Diffusion Signup and view all the answers

What is required for Active Transport to occur?

ATP hydrolysis Signup and view all the answers

Which type of transport utilizes the kinetic energy of one substance to drive the transport of another substance against its gradient?

Secondary Active Transport Signup and view all the answers

What characteristic defines gated channels in membranes?

They change shape to open or close the channel. Signup and view all the answers

What mediates the functioning of ligand-gated channels in cell membranes?

Chemical agent binding Signup and view all the answers

What property of protein channels ensures selectivity in the diffusion of molecules?

Size and electric charge of the pore loops Signup and view all the answers

Which of the following describes a characteristic of primary active transport?

It uses energy from ATP to move substances against their gradient. Signup and view all the answers

Which type of transport protein undergoes a conformational change to transport molecules across the membrane?

Carrier protein Signup and view all the answers

Which type of membrane transport does NOT require direct ATP consumption?

Secondary Active Transport Signup and view all the answers

What identifies the role of voltage-gated channels in the cell membrane?

They respond to changes in membrane potential. Signup and view all the answers

What happens when the outward diffusion of K+ ions is repelled by the electromagnetic force?

Equilibrium is reached when the charge buildup prevents further diffusion. Signup and view all the answers

How is the membrane potential at equilibrium primarily determined?

By the concentration gradient of ions. Signup and view all the answers

Which equation describes the balance between chemical diffusion and electrical repulsion in ions?

Nernst Equation Signup and view all the answers

What is the equilibrium potential for K+ ions calculated using the Nernst Equation?

-90 mV Signup and view all the answers

What is the typical resting membrane potential in neurons, despite the K+ equilibrium potential being -90 mV?

-70 mV to -80 mV Signup and view all the answers

What initiates the creation of a diffusion pore in voltage-gated channels?

Changes in the conformation of channel subunits. Signup and view all the answers

What role does the S4 segment play in the function of voltage-gated channels?

It acts as a voltage sensor that changes position in response to membrane polarization. Signup and view all the answers

What occurs when the membrane is depolarized to around -50 mV?

The S4 segment returns to the up position, removing structural occlusion from the pore. Signup and view all the answers

What is the primary function of endocytosis in the context of cellular processes?

To capture proteins from the outside and transport them inside. Signup and view all the answers

Which statement best describes exocytosis?

It facilitates the bulk transport of specific molecules from inside to outside of the cell. Signup and view all the answers

What characterizes the 'Kiss and Run' mechanism of exocytosis?

Fusion pores allow repeated docking Signup and view all the answers

Why is full exocytosis essential for cells?

It allows for high levels of signaling. Signup and view all the answers

What is the role of the enzyme ion pump in generating membrane potential?

It actively transports ions to create a concentration gradient. Signup and view all the answers

What condition is necessary for a membrane to create a membrane potential?

Selective permeability to specific ions. Signup and view all the answers

In which scenario would you expect the 'Kiss and Run' mechanism to be favored?

High signaling demands where rapid response is needed. Signup and view all the answers

What is a consequence of full exocytosis in a cell?

Increased surface area from vesicle fusion. Signup and view all the answers

Which process must occur alongside exocytosis to maintain membrane equilibrium?

Endocytosis Signup and view all the answers

What happens to the contents of a vesicle during the 'Kiss and Run' mechanism?

Only part of the contents are released at a time. Signup and view all the answers

Study Notes

Cell Membrane Overview

Cell membrane is a dynamic structure, not simply a passive barrier.
Composed of a phospholipid bilayer that selectively allows permeability.
Lipid-soluble substances (gases like O2 and CO2) can diffuse easily; water-soluble substances require assistance.
Impermeable to organic anions, such as proteins; permeability varies with molecular size, lipid solubility, and charge.

Membrane Transport Mechanisms

Simple Diffusion: Small lipid-soluble molecules diffuse through the membrane down their concentration gradients without ATP.
Facilitated Diffusion: Carrier proteins assist in transporting polar molecules (like sugars and amino acids) down their concentration gradient without ATP.
Active Transport: Moves substances against their concentration gradient using energy from ATP hydrolysis; includes mechanisms like the Na+/K+ pump.
Secondary Active Transport: Uses the kinetic energy of one substance moving down its gradient to transport another substance up its gradient without ATP.

Membrane Channels

Membrane channels are composed of 4-5 protein subunits creating a central pore for selective ion diffusion.
Channel selectivity is determined by size and charge; includes:
- Ligand-Gated Channels: Open in response to the binding of a chemical signal.
- Voltage-Gated Channels: Open or close in response to changes in membrane potential.

Endocytosis and Exocytosis

Endocytosis: Process of inward membrane pinching to form vesicles, often receptor-mediated.
Exocytosis: Involves vesicle fusion with the membrane to transport substances outside the cell.
- Kiss and Run: Vesicles can attach and detach multiple times, releasing partial contents.
- Full Exocytosis: Complete fusion releasing all contents, essential for high signaling levels and membrane protein delivery.

Membrane Potential (MP)

All cells generate a Membrane Potential (MP) through a concentration gradient and semi-permeable membrane.
MP is established when ion species diffuse across the membrane creating an electrical gradient.
Ion pumps (like the Na+/K+ pump) are critical in maintaining concentration gradients for MP.

Resting Membrane Potential (RMP)

Neurons have an RMP around -70 to -80 mV, influenced by the diffusion of K+ ions.
The equilibrium potential for K+ can be calculated as EK+ = (RT/F) ln([K+]o / [K+]i), resulting in -90 mV if only K+ ions are considered.

Nernst Equation

Describes the balance between chemical diffusion work and the electrical work of repulsion.
Used to calculate the equilibrium potential across the membrane for a specific ion species.

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Description

This quiz covers key concepts related to the cell membrane from PSL300's Lecture 01. Topics include cell membrane permeability, transport mechanisms like diffusion and active transport, as well as membrane potential and its importance in cellular functions. Test your understanding of these fundamental biological processes.