Cell Biology: Membrane Transport Mechanisms

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Questions and Answers

What is the main purpose of ATP in secondary active transport?

To facilitate the movement of one solute to drive another (correct)

To directly fuel the movement of molecules across the membrane

To increase the concentration of Na⁺ inside the cell

To open ion channels for faster diffusion

What is the primary function of the Na⁺-K⁺ pump?

Maintaining high intracellular Na⁺ concentration

Pumping Na⁺ out and K⁺ in to regulate membrane potential (correct)

Transporting glucose via passive transport

Facilitating the diffusion of water across the membrane

Which type of coupled transport involves the movement of molecules in opposite directions?

Aquaporins

Antiporters (correct)

Symporters

Ion channels

Which of the following describes the function of passive transport?

Random movement of particles without energy input (A) Signup and view all the answers

Which channel is more selective for sodium ions over potassium ions?

Na⁺ channel (B) Signup and view all the answers

What role do ABC transporters play in cells?

Exporting drugs and toxins from the cell (D) Signup and view all the answers

What does facilitated diffusion rely on?

Conformational changes in carrier proteins (A) Signup and view all the answers

Which transport mechanism is characterized by the direct use of ATP?

Primary active transport (D) Signup and view all the answers

What is the role of aquaporins in cellular function?

To facilitate osmosis of water selectively (A) Signup and view all the answers

Which of the following molecules would likely use facilitated diffusion to cross the plasma membrane?

Amino acids (B) Signup and view all the answers

Which type of transport uses the gradual change in ion concentration across a membrane?

Secondary active transport (B) Signup and view all the answers

In which scenario would the Na⁺-K⁺ pump primarily operate?

When high intracellular Na⁺ prevents secondary transport (B) Signup and view all the answers

Which condition would most likely increase the speed of diffusion for small molecules?

Increase in concentration gradient (A) Signup and view all the answers

What describes the process of osmosis?

Diffusion of water across a semi-permeable membrane (A) Signup and view all the answers

Voltage-gated ion channels open in response to changes in which of the following?

Electrical membrane potential (A) Signup and view all the answers

What defines the selectivity of ion channels?

The size and chemical nature of the ions (D) Signup and view all the answers

What is typically the result of using a proton pump in stomach cells?

Increased acidity (D) Signup and view all the answers

What is one consequence of having high intracellular Ca²⁺ concentration?

Cellular signal disruption (A) Signup and view all the answers

Which type of transport does not require energy input?

Facilitated diffusion (B) Signup and view all the answers

The Na⁺/glucose co-transporter operates primarily as what type of transport mechanism?

Symporter facilitated transport (D) Signup and view all the answers

Which transport system would most likely be affected by the overexpression of an MDR transporter?

Active expulsion of drugs from the cell (A) Signup and view all the answers

What does symporter transport involve?

Importing molecules in the same direction (B) Signup and view all the answers

What occurs during osmosis in terms of solute concentration?

Water moves to areas of higher solute concentration (D) Signup and view all the answers

The Na⁺/Ca²⁺ exchanger is an example of which type of transport?

Antiport transport (B) Signup and view all the answers

What condition is characteristic of primary active transport mechanisms?

Energy consumption for movements against the gradient (C) Signup and view all the answers

What is a common characteristic of the molecules that move through simple diffusion?

They are small or hydrophobic (D) Signup and view all the answers

Which type of transport does NOT utilize energy directly?

Facilitated diffusion (C) Signup and view all the answers

Study Notes

Transmembrane Transport of Small Molecules and Ions

Plasma membrane is selectively permeable, allowing specific molecules in and out of the cell. Nutrients enter and waste products exit, maintaining cell health.

Passive Transport

No energy input required; molecules move down their concentration gradient (high to low concentration).
Simple diffusion: Small, hydrophobic molecules (O2, CO2, steroids) move directly through the lipid bilayer.
Facilitated diffusion: Larger or charged molecules use transport proteins (channels or carriers). Examples include glucose and amino acids.
Osmosis: Water movement across a membrane down its osmotic gradient. Aquaporins are specialized channels allowing water passage.

Active Transport

Energy (typically ATP) is required to move molecules against their concentration gradient (low to high).
Primary active transport: Direct use of ATP. Examples include the Na+/K+ pump, calcium pump, and proton pump. These pumps maintain membrane potential and regulate cell volume.
Secondary active transport (Coupled transport): Uses the energy from one molecule moving down its gradient to move another molecule up its gradient. Includes symporters and antiporters.
- Symporters: Molecules move in the same direction. Example: Na+/glucose co-transporter.
- Antiporters: Molecules move in opposite directions. Example: Na+/Ca2+ exchanger.

Ion Channels

Channels allow specific ions to pass rapidly through the membrane.
Types: Voltage-gated, ligand-gated, and mechanosensitive.
- Voltage-gated: Open in response to changes in membrane potential.
- Ligand-gated: Open when a specific molecule (ligand) binds.
- Mechanosensitive: Respond to mechanical forces (e.g., stretching).
Selectivity: Narrow pores act as size filters, and interactions between the ion and channel components determine selectivity. Sodium channels (Na+ channels) are more selective for Na+ than K+, and potassium channels (K+ channels) are more selective for K+ than Na+.

Types of Transport Proteins:

Carriers: Bind to specific molecules and undergo conformational changes to transport them across the membrane . Example: GLUT-1 (glucose transporter).
Channels: Form pores allowing specific ions to pass quickly through the membrane. Examples include Na+ and K+ channels.

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Description

This quiz focuses on the transmembrane transport of small molecules and ions, covering both passive and active transport mechanisms. Understand the principles of diffusion, osmosis, and energy-dependent transport processes that maintain cellular function. Test your knowledge on how nutrients and wastes are managed by the plasma membrane.