Biology Chapter: Cell Membrane and Permeability

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Questions and Answers

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

Ions such as Na+ and K+

Lipid-soluble molecules and gases (correct)

Large polar molecules

Organic anions like proteins

Facilitated diffusion differs from simple diffusion primarily because it requires the assistance of what?

Carrier proteins (correct)

Cellular energy

Ionic gradients

Energy from ATP

What is the primary factor determining the permeability of a substance through the cell membrane?

Molecular size, lipid solubility, and charge (correct)

Temperature of the environment

Presence of specific receptors on the membrane

Concentration of solute inside the cell

What type of transport requires energy input from ATP?

Active transport Signup and view all the answers

What happens to the rate of facilitated diffusion when there are more substrates than transporter proteins?

It saturates and slows down Signup and view all the answers

Which process involves the movement of substances from an area of low concentration to high concentration?

Active transport Signup and view all the answers

Which of the following substances cannot cross the cell membrane without assistance?

Polar molecules Signup and view all the answers

Which mechanism is used by a cell to transport bulk materials into itself?

Endocytosis Signup and view all the answers

What is required for active transport to occur?

Energy from ATP hydrolysis Signup and view all the answers

Which process is described as using the kinetic energy of one substance to transport another against its gradient?

Secondary active transport Signup and view all the answers

What characterizes gated channels in membrane proteins?

They can be selectively closed or opened. Signup and view all the answers

How do ligand-gated channels operate?

They require the binding of a ligand for activation. Signup and view all the answers

What is the role of the 'gate' in gated channels?

To regulate the flow of ions based on environmental conditions. Signup and view all the answers

What type of substance binding triggers activation in ligand-gated channels?

A specific ligand Signup and view all the answers

What best describes primary active transport processes, such as the Na+/K+ pump?

They transport substances against their concentration gradient using ATP. Signup and view all the answers

Which factor is NOT a determinant of channel protein shape?

Membrane temperature Signup and view all the answers

What happens to the S4 segment of voltage-gated channels during depolarization?

It migrates downwards toward the inner membrane surface. Signup and view all the answers

What is the role of the S4 segment in voltage-gated channels?

It creates a pore for ion diffusion. Signup and view all the answers

At what membrane potential does depolarization no longer provide sufficient electrical attraction for the S4 segment?

-50 mV Signup and view all the answers

What occurs during exocytosis?

Vesicles fuse with the membrane to transport molecules outward. Signup and view all the answers

What mechanism typically mediates endocytosis?

Receptor-mediated processes. Signup and view all the answers

What happens to the S4 segment during hyperpolarization?

It is structured to close the pore. Signup and view all the answers

What characterizes the up position of the S4 segment?

It allows for the diffusion of ions through the channel. Signup and view all the answers

Which statement correctly defines depolarization in the context of cell membranes?

It refers to the influx of positive charges, moving towards less negative values. Signup and view all the answers

What is the primary function of Na+/K+ dependent ATPase?

To move Na+ out of the cell and K+ into the cell Signup and view all the answers

How many K+ ions are pumped into the cell for each ATP molecule broken down by Na+/K+ ATPase?

2 Signup and view all the answers

What is the approximate range of resting membrane potential in neurons?

-70 mV Signup and view all the answers

What happens to K+ ions when they diffuse out of the cell?

Diffusion is stopped due to increased electrical repulsion Signup and view all the answers

What role do K+ channels play in resting membrane potential?

They enable K+ ions to diffuse out of the cell Signup and view all the answers

At equilibrium, what balances the diffusion of cations outwards?

Electrical repulsion created by increased positive charge outside Signup and view all the answers

What percentage of energy needs of the body is consumed by Na+/K+ ATPase?

1/3 Signup and view all the answers

What is the primary function of the Na+/K+ pump in cell membranes?

To create concentration gradients of ion species Signup and view all the answers

What characterizes the 'Kiss and Run' exocytosis mechanism?

Repeated connection and disconnection of vesicle Signup and view all the answers

Which statement best describes full exocytosis?

Total release of vesicle contents occurs at once. Signup and view all the answers

Which of the following is necessary for generating membrane potential?

Presence of ion concentration gradients and a semi-permeable membrane Signup and view all the answers

What happens to vesicle contents during the 'Kiss and Run' process?

Contents only partially diffuse into surrounding fluid. Signup and view all the answers

What may help to stabilize membrane surface area in conjunction with exocytosis?

Endocytosis Signup and view all the answers

What role does enzyme ion pumps play in membrane potential?

They create concentration gradients for specific ions. Signup and view all the answers

How do fusion pores function during exocytosis?

They enable temporary connection between the vesicle and membrane. Signup and view all the answers

Study Notes

Cell Membrane

Composed of phospholipid bilayer, crucial for cell structure and function.
Lipid-soluble molecules easily diffuse through, while water-soluble molecules require assistance to cross.
Impermeable to organic anions such as proteins; permeability is influenced by size, lipid solubility, and charge.

Membrane Permeability

Permeability indicates if a substance can cross the membrane freely or with assistance.
Gases can diffuse directly, while polar molecules and ions need specific proteins or channels.

Simple Diffusion

Occurs for small, lipid-soluble molecules like O2 and CO2, moving down their concentration gradient.
Passive process requiring no ATP, with diffusion rate proportional to concentration gradient.

Facilitated Diffusion

Involves carrier proteins assisting in the movement of polar molecules, such as sugars and amino acids, down their concentration gradient.
Also passive, relying on the concentration gradient for energy.

Active Transport

Mechanism for moving substances against their concentration gradient via a carrier protein.
Requires energy from ATP hydrolysis, exemplified by the Na+/K+ pump.

Secondary Active Transport

Utilizes the energy from one substance's movement down its concentration gradient to drive another substance against its gradient.
Involves a transporter protein which undergoes conformational changes to facilitate movement.

Channels

Membrane channels are protein structures forming pores, allowing specific ions to diffuse.
Selectivity is determined by the size and charge of the molecules allowed through.

Gated Channels

Channels can open or close based on protein shape changes, regulated by factors like ligand binding or voltage changes.

Ligand Gated Channels

Respond to the binding of specific chemical ligands, triggering cellular signaling events.

Voltage Gated Channels

Sensitive to membrane potential; conformational changes allow ion diffusion in response to depolarization.

Endo/Exocytosis

Endocytosis involves membrane pinching to form vesicles and transport substances into the cell, usually receptor-mediated.
Exocytosis is the fusion of vesicles with the membrane to release or transport materials outside the cell, essential for signaling.

Exocytosis Types

Kiss and Run: vesicles fuse temporarily at docking sites, allowing partial content release and repeated use.
Full Exocytosis: complete vesicle fusion resulting in total content release, critical for high-volume signaling.

Membrane Potential

Generated by ion concentration gradients and a selectively permeable membrane.
The Na+/K+ pump actively establishes these gradients, moving 3 Na+ out and 2 K+ in for each ATP consumed.

Resting Membrane Potential (RMP)

Neurons exhibit a resting potential closer to -70 mV due to higher permeability to K+ ions.
K+ ions diffuse out, leading to a net negative charge inside the cell, influenced by both concentration and electrical gradients.

Equilibrium Potential

At equilibrium, the electrical force opposing K+ efflux balances the chemical force driving K+ out, resulting in a stable resting membrane potential.

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Description

Explore the essential concepts of cell membranes, including their structure and function. Understand the mechanisms of diffusion and permeability, distinguishing between simple and facilitated diffusion. This quiz covers the crucial aspects of how substances interact with the cell membrane.