GLUT Transporters Overview

Questions and Answers

What is the primary function of GLUT2 in relation to blood glucose levels?

It mediates glucose release from adipocytes.

It increases glucose uptake in muscle cells.

It decreases glucose transcription in pancreatic cells.

It regulates blood glucose levels by transporting glucose during high blood glucose conditions. (correct)

Which GLUT transporter is specifically regulated by insulin?

GLUT3

GLUT4 (correct)

GLUT1

GLUT2

What characteristic differentiates GLUT3 from GLUT2?

GLUT3 has a high Km, while GLUT2 has a low Km.

GLUT3 is abundant in muscle while GLUT2 is found in the liver.

GLUT3 possesses a low Km indicating high affinity for glucose. (correct)

GLUT3 is regulated by insulin.

Which type of ion channel is primarily influenced by the binding of a specific ligand?

Ligand-gated channel Signup and view all the answers

What event triggers the movement of GLUT4 vesicles to the plasma membrane?

Insulin binding to its receptor. Signup and view all the answers

What distinguishes the Jmax characteristic of GLUT2?

It reflects its high capacity to transport glucose when needed. Signup and view all the answers

What primary energy source does the Na+/K+ pump utilize for its Action?

Hydrolysis of ATP Signup and view all the answers

In which manner does the SGLUT function as a transporter?

Symport Signup and view all the answers

How does digitoxin affect cardiac muscle contraction?

Blocks the dephosphorylation step in Na+/K+ pump Signup and view all the answers

What is the main consequence of increased chloride ion secretion induced by cholera toxin?

Dehydration due to osmosis Signup and view all the answers

What characterizes the Na+/Ca2+ cotransporter in muscle cells?

It uses the Na+ gradient established by the Na+/K+ pump. Signup and view all the answers

Which ion channel is affected by mutations leading to cystic fibrosis?

Chloride channel Signup and view all the answers

What happens to intracellular Ca2+ levels when the Na+/K+ pump is inhibited?

They increase due to failure of the Na+/Ca2+ antiport. Signup and view all the answers

What type of transport system is utilized by the Na+/K+ pump?

Primary active transport Signup and view all the answers

What role does ATP play in the function of CFTR?

It phosphorylates the channel to activate it. Signup and view all the answers

Which transport type allows Na+ to move with glucose across the intestinal membrane?

Secondary active transport Signup and view all the answers

What characteristic is true regarding small uncharged polar molecules crossing the membrane?

They can cross the membrane by simple diffusion. Signup and view all the answers

Which of the following describes the Na+/K+-ATPase membrane pump?

It pumps sodium ions out of the cell and potassium ions into the cell. Signup and view all the answers

Which type of transport relies on specific proteins to allow charged polar molecules to cross the membrane?

Both facilitated diffusion and active transport Signup and view all the answers

What is indicated by a lower Km value for a transporter?

Higher affinity for the solute Signup and view all the answers

Which of the following molecules would most likely have the highest permeability across a lipid bilayer?

Oxygen Signup and view all the answers

What is the function of GLUT glucose transporters?

Mediating facilitated diffusion of glucose. Signup and view all the answers

How does facilitated diffusion differ from simple passive transport?

Facilitated diffusion requires specific membrane proteins. Signup and view all the answers

What type of molecules generally require specific proteins for membrane transport due to their properties?

Charged polar molecules Signup and view all the answers

Which statement best describes simple passive transport?

Solutes move down a concentration gradient. Signup and view all the answers

Which of the following scenarios best illustrates secondary active transport?

Glucose is transported into a cell along with sodium ions. Signup and view all the answers

Study Notes

Membrane Transport Overview

Membranes function as selective permeability barriers, restricting hydrophilic molecule passage.
Small uncharged or hydrophobic molecules cross via simple diffusion along concentration gradients.
Charged polar molecules require specific proteins (pumps, transporters, pores) to traverse membranes.

Mechanisms of Transport

Types of transport include:
- Simple passive transport/Diffusion
- Facilitated diffusion
- Gated ion channels
- Primary active transport
- Secondary active transport

Passive Transport

Solutes move down their concentration gradient, achieving equilibrium inside and outside the cell.
Rate of diffusion linked to the solute's Partition Coefficient; more hydrophobic solutes equilibrate rapidly.
Example solutes include O2, CO2, H2O, urea, and glucose.

Facilitated Diffusion

Requires membrane proteins for solute movement across membranes, such as ion channels and specific transporters.
Examples include Cl-/HCO3- channels in erythrocytes, aquaporin water channels, and GLUT glucose transporters.

Glucose Transporters (GLUT)

GLUT1: Low Km (~1.8mM), high affinity, found in various tissues for constitutive glucose uptake.
GLUT2: High Km (~20mM), transports glucose into liver and pancreatic cells when blood glucose is high.
GLUT3: Located in neurons with low Km, high affinity for glucose.
GLUT4: Regulated by insulin, present in muscle and adipose tissues; facilitates glucose uptake via membrane recruitment.

Gated Ion Channels

Allow selective facilitated diffusion for specific ions (K+, Na+, Ca2+).
Open or close in response to stimuli:
- Ligand-gated (e.g., acetylcholine receptors)
- Voltage-gated (e.g., Na+ and K+ channels in axons)

Active Transport

Solutes move against concentration gradients, requiring membrane proteins and energy (ATP hydrolysis).
Example: Na+/K+ ATPase pump maintains Na+ and K+ gradients crucial for nerve transmission.

Na+/K+ Pump

Tetramer (α2β2) structure of the pump facilitates Na+ entry and K+ export.
Conformational changes driven by ATP phosphorylation regulate ion binding and release.

Co-Transport Systems

Utilize pre-established gradients to transport solutes against gradients using ATP-driven primary gradients.
Includes symport (same direction) and antiport (opposite direction).

Na+-Glucose Cotransporter (SGLUT)

Facilitates glucose absorption in the intestine against its gradient using the Na+ gradient.
Functions as a symport, with Na+ driving glucose uptake into cells.

Na+/Ca2+ Cotransporter

Exports Ca2+ from muscle cells against its concentration gradient using Na+ as an antiport.

Clinical Considerations

Cardiac Glycosides (Digitoxin/Ouabain): Inhibit Na+/K+ pump, increasing intracellular Na+ concentrations, thereby diminishing Ca2+ export and enhancing heart muscle contractions.
Cystic Fibrosis (CF): Caused by CFTR mutations, impacting chloride ion transport and leading to thick mucus production, resulting in lung blockages.
Cholera Treatment: Vibrio cholerae prompts increased secretion of Cl- ions via CFTR, while oral rehydration therapy includes high glucose to enhance Na+ uptake through SGLUT, promoting water absorption.

Summary

Membrane transport includes various mechanisms such as passive transport, facilitated diffusion, active transport, and co-transport.
GLUT transporters and the Na+/K+ pump play critical roles in cellular glucose uptake and ion homeostasis, with clinical implications in diseases like cystic fibrosis and heart conditions.

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Description

This quiz focuses on GLUT transporters, specifically GLUT2, and their role in glucose uptake in various tissues. It highlights key characteristics such as affinity, capacity, and physiological relevance in regulating blood glucose levels. Explore the importance of these transporters in the liver and pancreatic cells.