Transmembrane Transport of Molecules

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Questions and Answers

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

Keeps high Na⁺ concentrations inside the cell

Excretes calcium ions for metabolic processes

Maintains membrane potential and regulates cell volume (correct)

Facilitates passive transport of glucose

Which transport process involves the movement of molecules against their concentration gradient using energy?

Active transport (correct)

Simple diffusion

Passive transport

Facilitated diffusion

What is the role of the calcium pump in a cell?

To export hydrogen ions to regulate pH

To maintain high intracellular sodium levels

To keep low intracellular calcium concentrations (correct)

To import nutrients like glucose

Which of the following is not a characteristic of passive transport?

It can move ions against their electrochemical gradient (B) Signup and view all the answers

What type of molecules can most easily permeate the plasma membrane without assistance?

Hydrophobic molecules like O₂ and CO₂ (A) Signup and view all the answers

What is one function of ABC transporters in cells?

To actively pump out drugs and toxins from the cell (A) Signup and view all the answers

Na⁺ ions can sometimes accumulate in cells due to the inhibition of which transporter?

Na⁺-K⁺ pump (C) Signup and view all the answers

In the process of osmosis, which of the following statements is true?

Water moves from low solute concentration to high solute concentration (A) Signup and view all the answers

Which type of transport specifically utilizes ATP to transport ions across a membrane?

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

What is a characteristic of symporters in cellular transport?

They allow molecules to move in the same direction (B) Signup and view all the answers

Which of the following accurately describes facilitated diffusion?

It employs transport proteins for larger or charged molecules (D) Signup and view all the answers

What role does the proton pump play in stomach cells?

It exports hydrogen ions to regulate acidity (D) Signup and view all the answers

What is a key feature of multidrug resistance (MDR) transporters?

They export a range of drugs out of tumor cells (B) Signup and view all the answers

Which of the following best describes the process of simple diffusion?

It occurs when molecules move down their concentration gradient without assistance (D) Signup and view all the answers

What is the primary function of antiporters in secondary active transport?

To transport two different ions or molecules in opposite directions (C) Signup and view all the answers

What role do ion channels play in facilitated diffusion?

They allow specific ions to pass through based on size and charge (A) Signup and view all the answers

Which of the following is an example of facilitated diffusion?

GLUT-1 glucose transporter (C) Signup and view all the answers

What differentiates symporters from antiporters in coupled transport mechanisms?

Symporters transport two molecules in the same direction, while antiporters transport in opposite directions (C) Signup and view all the answers

Which type of transport directly requires ATP to function?

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

What characteristic allows aquaporins to selectively facilitate the movement of water?

They have narrow pores that block all ions (D) Signup and view all the answers

What process describes the movement of water across a membrane down its osmotic gradient?

Osmosis (D) Signup and view all the answers

What type of ion channel opens in response to specific ligands binding?

Ligand-gated channels (C) Signup and view all the answers

How does the concentration gradient affect the rate of diffusion?

A larger gradient increases the rate of diffusion (C) Signup and view all the answers

Which channels are specifically selective for Na⁺ ions over K⁺ ions?

Na⁺ channels (C) Signup and view all the answers

Which of the following types of channels respond to mechanical forces?

Mechanosensitive channels (A) Signup and view all the answers

What is the primary difference between passive and active transport mechanisms?

Active transport requires ATP, while passive transport does not (A) Signup and view all the answers

What is the result of the conformational change in carrier proteins during transport?

It aids in the selective transport of specific molecules across the membrane (B) Signup and view all the answers

Study Notes

Transmembrane Transport of Small Molecules and Ions

Plasma Membrane: Semi-permeable, regulating what enters and exits the cell. Controls movement of essential nutrients, metabolites, and waste.

Passive Transport (No Energy Input)

Simple Diffusion: Movement of small, hydrophobic molecules (e.g., O₂, CO₂, steroids) across the lipid bilayer without assistance. Speed depends on concentration gradient.
Facilitated Diffusion: Movement of larger or charged molecules (e.g., glucose, amino acids) assisted by transport proteins (channels or carriers). Molecules move down their concentration gradient.
Osmosis: Movement of water across a membrane down its osmotic gradient. Water moves through aquaporins.

Active Transport (Energy Input Required)

Primary Active Transport: Direct use of energy (often ATP) to move molecules against their concentration gradient.
- Na⁺-K⁺ Pump: Pumps 3 Na⁺ out and 2 K⁺ in, maintaining membrane potential and cell volume.
- Calcium Pump: Maintains low intracellular Ca²⁺ concentration. Essential for numerous cellular processes.
- Proton Pump: Involved in regulating acidity in stomach cells and organelles.
- ABC Transporters (ATP-binding cassette): Large family of transporters involved in importing nutrients, exporting toxins, and drugs. Overexpression is linked to drug resistance.
Secondary Active Transport (Coupled Transport): Uses energy from the movement of one molecule down its concentration gradient to move another molecule against its gradient.
- Symporters: Molecules move in the same direction (e.g., Na⁺/glucose co-transporters in intestines).
- Antiporters: Molecules move in opposite directions (e.g., Na⁺/Ca²⁺ exchanger in cardiac cells, Na⁺/H⁺ exchanger).

Ion Channels

Types: Voltage-gated, ligand-gated, and mechanosensitive.
Selectivity: Based on size and charge. Precise interactions within narrow pores determine selectivity (e.g., Na⁺ channels more selective for Na⁺; K⁺ channels more selective for K⁺).
Function: Allow specific ions to rapidly pass through the membrane.

Specific Examples

GLUT-1 (glucose transporter): Facilitated diffusion to transport glucose.
MDR transporters (multidrug resistance): ABC transporters that export drugs and other substances.
CFTR (Cystic Fibrosis Transmembrane Conductance Regulator): ABC transporter critical for proper ion transport, especially chloride, in the lungs.

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Description

This quiz covers the mechanisms of transmembrane transport, including passive and active transport processes. It explores simple diffusion, facilitated diffusion, osmosis, and primary active transport. Understanding these concepts is essential for grasping how cells regulate their internal environment.