Transmembrane Transport of Molecules

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Questions and Answers

Which of the following is NOT a characteristic of facilitated diffusion?

  • It is a passive transport process.
  • It requires a transmembrane protein to move molecules across the membrane.
  • It moves molecules against their concentration gradient. (correct)
  • It is a type of transport that is specific for certain molecules.

What is the main difference between simple diffusion and facilitated diffusion?

  • Simple diffusion is a passive transport process, while facilitated diffusion is an active transport process.
  • Simple diffusion moves molecules down their concentration gradient, while facilitated diffusion moves molecules against their concentration gradient.
  • Simple diffusion can transport larger molecules, while facilitated diffusion can only transport small molecules.
  • Simple diffusion requires a membrane protein, while facilitated diffusion does not. (correct)

Which of the following is an example of secondary active transport?

  • The movement of glucose into the cell along with sodium ions (Na+) using a symporter. (correct)
  • The movement of oxygen (O2) across the membrane by simple diffusion.
  • The movement of water across the membrane through aquaporins.
  • The movement of sodium ions (Na+) out of the cell using the sodium-potassium pump.

What is the role of the sodium-potassium pump in coupled transport?

<p>It creates a concentration gradient of sodium ions (Na+) that can then be used to drive the movement of other molecules. (D)</p> Signup and view all the answers

What is the primary function of aquaporins?

<p>To facilitate the movement of water across the membrane. (D)</p> Signup and view all the answers

Which of the following is NOT a type of ion channel?

<p>Ligand-dependent (C)</p> Signup and view all the answers

Which of the following is an example of an antiporter?

<p>The sodium-calcium exchanger. (C)</p> Signup and view all the answers

What is the main difference between a carrier protein and an ion channel?

<p>Carrier proteins transport molecules across the membrane through conformational changes, while ion channels create a pore through the membrane. (D)</p> Signup and view all the answers

What is the main factor that determines the rate of simple diffusion?

<p>The concentration gradient of the molecule. (C)</p> Signup and view all the answers

Which of the following is TRUE about the selectivity of ion channels?

<p>They are selective for specific ions based on a combination of size and charge. (A)</p> Signup and view all the answers

What is the main difference between a symporter and an antiporter?

<p>A symporter moves two molecules in the same direction, while an antiporter moves two molecules in opposite directions. (C)</p> Signup and view all the answers

Which of the following statements about the sodium-potassium pump is TRUE?

<p>It is a type of antiporter that moves sodium ions (Na+) and potassium ions (K+) in opposite directions. (B)</p> Signup and view all the answers

What is the role of the acetylcholine receptor at the neuromuscular junction?

<p>It is a ligand-gated ion channel that opens when acetylcholine binds to it, allowing sodium ions (Na+) to enter the muscle cell. (C)</p> Signup and view all the answers

What is the main difference between osmosis and diffusion?

<p>Osmosis involves the movement of water, while diffusion involves the movement of any type of molecule. (D)</p> Signup and view all the answers

Which of the following statements about the movement of molecules across the membrane is TRUE?

<p>Small, uncharged molecules can move easily across the membrane by simple diffusion. (D)</p> Signup and view all the answers

Which of the following statements about coupled transport is TRUE?

<p>It uses the energy from the movement of one molecule down its concentration gradient to drive the movement of another molecule up its concentration gradient. (B)</p> Signup and view all the answers

Which of these transport mechanisms directly uses ATP to move molecules against their concentration gradient?

<p>Primary Active Transport (D)</p> Signup and view all the answers

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

<p>To create a concentration gradient of sodium ions outside and potassium ions inside the cell (A)</p> Signup and view all the answers

What type of transport mechanism is used by ABC transporters?

<p>Primary Active Transport (A)</p> Signup and view all the answers

How does MDR transporter contribute to drug resistance?

<p>By exporting drugs out of the cell (C)</p> Signup and view all the answers

Which of the following transport mechanisms does NOT require energy input?

<p>Simple Diffusion (C)</p> Signup and view all the answers

What is the role of the calcium pump in maintaining cellular function?

<p>To maintain a low intracellular calcium concentration (B)</p> Signup and view all the answers

Which of the following statements about secondary active transport is TRUE?

<p>It uses the energy stored in an existing concentration gradient to move another molecule (B)</p> Signup and view all the answers

What type of transport mechanism is responsible for the movement of water across the cell membrane?

<p>Osmosis (B)</p> Signup and view all the answers

Which of the following molecules is LEAST likely to move across the cell membrane by simple diffusion?

<p>Glucose (D)</p> Signup and view all the answers

What is the significance of the proton pump in regulating the acidity of stomach cells?

<p>It pumps protons into the stomach lumen, increasing acidity (C)</p> Signup and view all the answers

Which of the following transport proteins is responsible for the transmembrane conductance of chloride ions in cystic fibrosis?

<p>CFTR (C)</p> Signup and view all the answers

Which of the following statements regarding symporters is TRUE?

<p>They move molecules in the same direction (C)</p> Signup and view all the answers

Why is the Na⁺-K⁺ pump often considered essential for secondary active transport?

<p>It creates a concentration gradient that powers secondary transporters (A)</p> Signup and view all the answers

The accumulation of Na+ ions inside the cell has what consequence on secondary active transport?

<p>It decreases the efficiency of secondary active transport (D)</p> Signup and view all the answers

What is the primary reason that water moves through a semi-permeable membrane from a high water potential to a low water potential?

<p>Osmosis, as the driving force is a difference in water concentration (D)</p> Signup and view all the answers

Flashcards

ATP Usage in Transport

ATP is required to pump Na+ out of cells during secondary active transport.

Coupled Transport

Movement of one solute drives the movement of another in cells, can be symport or antiport.

Secondary Active Transport

Uses energy from moving one molecule down its gradient to move another up its gradient.

Antiporters

Transport proteins that move molecules in opposite directions across a membrane.

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Symporters

Transport proteins that move two or more molecules in the same direction across a membrane.

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Simple Diffusion

Movement of small, nonpolar molecules (O₂, CO₂) across the membrane without energy use.

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Facilitated Diffusion

Transport of molecules across a membrane via specific proteins, without energy input.

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Ion Channels

Transmembrane proteins that allow specific ions to move across membranes rapidly.

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Voltage-gated Channels

Ion channels that open or close in response to changes in membrane potential.

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Ligand-gated Channels

Ion channels that open upon binding with a specific molecule (ligand).

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Mechanosensitive Channels

Ion channels that respond to mechanical forces, such as stretch or pressure.

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Osmosis

Movement of water across a membrane down its osmotic gradient.

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Aquaporins

Specialized channels that allow water to pass through membranes, blocking ions.

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Ion Selectivity

Channels show preference for specific ions based on size and charge.

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GLUT-1 Transporter

A type of glucose transporter that allows glucose to enter cells through facilitated diffusion.

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Na⁺-K⁺ Pump

A transport mechanism that pumps 3 Na⁺ out and 2 K⁺ in against their gradients, using ATP.

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Primary Active Transport

Transport that requires energy to move substances against their concentration gradient.

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Calcium Pump

Transporter that maintains low intracellular Ca²⁺ concentration using ATP.

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Proton Pump

Moves protons across membranes, regulates acidity in stomach and organelles.

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Semi-permeable Membrane

A membrane that allows certain molecules to pass while excluding others.

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Passive Transport

Movement of molecules across the membrane without energy input.

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ABC Transporters

A large family of proteins that use ATP hydrolysis to transport various molecules across membranes.

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MDR Transporter

Multidrug resistance transporter that pumps drugs out of cells.

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CFTR

Cystic Fibrosis Transmembrane Conductance Regulator, involved in ion transport.

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Importers & Exporters

Proteins that import nutrients and export waste or toxins across membranes.

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Cell Membrane Functions

Regulates transport, maintains cell volume and membrane potential, and protects cell interiors.

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Study Notes

Transmembrane Transport of Small Molecules and Ions

  • Plasma Membrane: Semi-permeable, controlling entry and exit of molecules.
  • Passive Transport: Movement without energy input, follows concentration gradient.
    • Simple Diffusion: Small, hydrophobic molecules (O2, CO2, steroids) pass directly through the lipid bilayer.
    • Facilitated Diffusion: Larger/charged molecules use transport proteins (channels or carriers). Examples include GLUT-1 (glucose transporter).
    • Osmosis: Movement of water across a membrane down its osmotic gradient, often through aquaporins.
  • Active Transport: Requires energy (usually ATP) to move molecules against their concentration gradient.
    • Primary Active Transport: Direct use of ATP. Examples include Na+/K+ pump, calcium pump, proton pump.
    • Secondary Active Transport (Coupled Transport): Uses energy from one molecule moving down its gradient to move another molecule up its gradient. Examples include symporters (e.g., Na+/glucose co-transporter) and antiporters (e.g., Na+/Ca2+ exchanger).
  • Ion Channels: Pathways for specific ions to rapidly pass through the membrane. Types include:
    • Voltage-gated: Open/close in response to changes in membrane potential.
    • Ligand-gated: Open/close when a specific molecule (ligand) binds.
    • Mechanosensitive: Respond to mechanical forces (e.g., stretching).
  • Ion Selectivity: Channels are selective, allowing specific ions to pass.
  • Carrier Proteins: Bind to a molecule and then undergo conformational changes to transport it.

Key Transporters

  • Na+/K+ Pump: Pumps 3 Na+ out and 2 K+ in per ATP hydrolyzed. Maintains membrane potential and regulates cell volume.
  • Calcium Pump: Maintains low intracellular Ca2+ concentration.
  • Proton Pump: Regulates acidity in stomach cells and organelles.
  • ABC Transporters (ATP-binding cassette): Largest family of ATP-hydrolysis-coupled transporters. Import nutrients and export toxins/drugs/antibiotics.
    • Specific Examples: MDR transporter (multidrug resistance) and CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) are categorized as ABC transporters.

Active Transport

  • Mechanisms: Secondary active transport couples the movement of one solute to the movement of another.
  • Importance: Maintains gradients and allows cells to accumulate essential nutrients and export toxins.

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