Skip to content
Login Register

#active transport

14 public questions tagged with this topic.

Basics of Cell Biology

Which of the following types of transport requires ATP?

Membrane transport classification depends on thermodynamics and mechanism. Simple diffusion of lipophilic gases O2, CO2, steroids occurs directly through hydrocarbon core partitioning driven solely by concentration gradient without protein. Facilitated diffusion via channels like aquaporins and carriers like GLUT1 enhances polar solute permeation down gradient, increasing rate and specificity, still entropy-driven, saturable, no ATP hydrolysis. Osmosis is water movement across semipermeable membrane toward solute, also passive. Active transport moves substrates against electrochemical potentia

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 11: Active Transport Requires ATP.

View Details
Plasma Membrane

Which type of membrane transport is facilitated by transmembrane proteins?

Passive entry of polar solutes across 4 nm hydrophobic core is energetically prohibited, necessitating membrane proteins that provide facilitated diffusion pathway without ATP input. Transmembrane proteins create two mechanisms: channel proteins like aquaporin-1, potassium channels with selectivity filter TVGYG, and porins with beta-barrels that form continuous aqueous pores allowing diffusion at rates approaching 10^8 ions per second down electrochemical gradient, gating regulated by voltage, ligand, or mechanical force. Carrier proteins like GLUT1 glucose transporter and AE1 anion exchanger

Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 11: Facilitated Diffusion and Transporters.

View Details
Membrane Transportation

Which of the following ions is not actively transported in most cells?

Cellular ion homeostasis requires continuous energy expenditure to maintain steep gradients. Sodium gradient high outside 145 millimolar low inside 12 millimolar and potassium opposite 4 outside 140 inside established by Na+/K+ ATPase hydrolyzing ATP forming phosphoenzyme E1P E2P cycling three sodium out two potassium in per ATP. Calcium gradient extreme low cytosolic 100 nanomolar versus 1 to 2 millimolar extracellular maintained by plasma membrane Ca2+ ATPase PMCA and sarcoplasmic endoplasmic reticulum Ca2+ ATPase SERCA, both P-type pumps transporting two calcium per ATP against ten thousand

Ref: Alberts et al., Molecular Biology of the Cell, Chapter 11: Ion Distributions - Cl- Passive vs Active Transport.

View Details
Membrane Transportation

The Na+/glucose transporter (SGLT1) is an example of:

Sodium-dependent glucose transport exemplifies secondary active symport coupling uphill absorption to downhill sodium entry. SGLT1 gene SLC5A1 located apically in intestinal villus enterocytes and kidney proximal tubule contains fourteen transmembrane helices in LeuT fold forming cavity with two sodium sites Na1 and Na2 plus glucose pocket recognizing hydroxyls. Cycle has ordered binding: two sodium ions bind first increasing affinity for D-glucose by opening outer gate then protein transitions from outward open to occluded to inward open releasing cargo inside. Both substrates move same direc

Ref: Wright et al., Journal of Biological Chemistry 2004: SGLT1 as Sodium Glucose Symport.

View Details
Membrane Transportation

Which process requires ATP?

Energy coupling distinguishes passive and active transport. Simple diffusion of gases, facilitated diffusion via carriers like GLUT and channels like aquaporin, and osmosis driven by water potential are passive, relying on thermal motion and existing gradients without ATP input, negative Gibbs free energy toward equilibrium. Primary active transport directly uses chemical energy from ATP hydrolysis within same protein to move solute against gradient. P-type ATPases like Na+/K+ ATPase exchanging 3 Na+ out for 2 K+ in, V-type H+ ATPase acidifying lysosomes, F-type ATP synthase reversible, and AB

Ref: Alberts et al., Molecular Biology of the Cell, 6th ed., Chapter 11: Primary Active Transport – ATP Requirement.

View Details
Membrane Transportation

The Na+/K+ ATPase pump is an example of:

Coupled transporters classified as antiporters exchange substrates in opposite directions driven by gradients. Sodium potassium ATPase exemplifies primary active antiporter using ATP rather than secondary gradient. Alpha subunit has ten transmembrane helices forming pocket with three sodium sites and two potassium sites. It binds three intracellular Na+ in high affinity E1 and exports them while binding two extracellular K+ and importing them, so Na+ and K+ move opposite in same cycle. Exchange is electrogenic due to 3:2 stoichiometry, contributing about minus four millivolts to potential and

Ref: Skou & Esmann, Journal of Bioenergetics 1992: Na+,K+-ATPase as Antiporter Mechanism.

View Details
Membrane Transportation

The Na+/K+ ATPase pump transports:

Sodium-potassium pump is archetypal P-type ATPase maintaining electrochemical gradients vital for volume control and excitability. Each cycle hydrolyzes one ATP to ADP and phosphate, driving conformational shift from E1 high Na+ affinity inward to E2 low affinity outward via phosphorylated Asp369 intermediate. In E1 facing cytosol, cavity binds three sodium ions, triggering autophosphorylation. Transition to E2-P exposes cavity extracellularly where Na+ affinity drops, sodium released and potassium sites exposed. Two extracellular potassium ions bind with high affinity in E2-P, inducing dephos

Ref: Skou & Esmann, Journal of Bioenergetics 1992: Na+,K+-ATPase Stoichiometry – 3 Na+ out, 2 K+ in.

View Details
Membrane Transportation

The transport of glucose into intestinal epithelial cells via SGLT1 is an example of:

Intestinal glucose absorption across absorptive enterocytes lining duodenum and jejunum illustrates elegant coupling of electrochemical gradients for nutrient uptake against concentration difference. Luminal sodium concentration remains high around 140 millimolar due to continuous activity of Na+/K+ ATPase on basolateral membrane pumping three Na+ out and two K+ in per ATP hydrolyzed, creating inward sodium electrochemical gradient with both chemical and electrical components. Sodium glucose cotransporter 1, SGLT1, SLC5A1 gene, located apically in brush border with fourteen transmembrane segme

Ref: Wright et al., Physiology Reviews 2011: Sodium-Glucose Cotransporter SGLT1 – Secondary Active Transport.

View Details
Membrane Transportation

Which of the following statements about membrane transport is true?

Plasma membrane selectively controls solute entry through distinct physico-chemical mechanisms dictated by molecular properties. Small non-polar gases such as O2, CO2, N2 and NO partition readily into hydrophobic core and cross by simple diffusion governed by Fick's law, without assistance, explaining lung alveolar exchange and mitochondrial oxygen supply. However many essential nutrients are hydrophilic or charged and face high energetic barrier. Facilitated diffusion provides protein-assisted route down concentration gradient without direct energy coupling, accelerating equilibration thousan

Ref: Alberts et al., Molecular Biology of the Cell, 6th ed., Chapter 11: Membrane Transport – Facilitated Diffusion Principles.

View Details
Endomembrane System - ER Golgi Lysosome Vacuole

Consider the following statements about transport across the plasma membrane: I. A neutral solute may move from higher t

Neutral solutes may diffuse down their concentration gradient without energy. Polar molecules require carrier proteins to cross the non-polar bilayer. Movement against a gradient is active transport and requires energy supplied through ATP.

Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Endomembrane System - ER Golgi Lysosome Vacuole

View Details