Questions and Answers
What is carrier-mediated transport?
Mechanisms in which a solute binds to a specific binding site on a carrier protein and is transported to the other side of the membrane.
What are the types of carrier-mediated transport?
What is the difference between primary and secondary active transport?
Primary active transport uses ATP as an energy source, while secondary active transport uses the energy from electrochemical gradients.
What is the difference between a carrier and a channel?
Signup and view all the answers
The steps in transport by a simple carrier (facilitated diffusion) include: 1. The carrier on the outside is open, 2. Solute enters and binds at the binding site, 3. The outer gate closes, 4. The inner gate opens while the solute is still bound, 5. The solute exits and enters the cell, and 6. The outer gate will remain closed while the inner gates close, occluding an empty binding site.
Signup and view all the answers
What does specificity mean in the context of carrier-mediated transport?
Signup and view all the answers
What is meant by saturation in transport mechanisms?
Signup and view all the answers
What is Jmax (Vmax)?
Signup and view all the answers
What is KM or Kt?
Signup and view all the answers
Which types of solutes need to use carrier-mediated transport to enter or exit cells?
Signup and view all the answers
What can determine the direction of net transport in uniporter and facilitated diffusion?
Signup and view all the answers
What is the role of ATP in primary active transport?
Signup and view all the answers
What can stop the Na+/K+ pump from the extracellular side?
Signup and view all the answers
What happens to a mammalian cell if the Na+/K+ pump stops?
Signup and view all the answers
What is an electroneutral transport mechanism?
Signup and view all the answers
What is co-transport (synport)?
Signup and view all the answers
The Na+/K+ pump is often called a _____
Signup and view all the answers
Study Notes
Carrier-Mediated Transport
- Definition: Involves specific binding of a solute to a carrier protein, facilitating transport across a membrane when the binding site is exposed to the other side.
Types of Carrier-Mediated Transport
- Facilitated Transport: Passive process requiring no energy, moves substances downhill.
- Active Transport: Requires energy to move substances against their concentration gradient.
Primary vs. Secondary Active Transport
- Primary Active Transport: Directly uses ATP for energy (e.g., ion pumps).
- Secondary Active Transport: Utilizes energy from electrochemical gradients (e.g., Na+ gradient).
Differences Between Carriers and Channels
- Carriers: Have two gates that are never open simultaneously; molecules are transported one at a time.
- Channels: Allow molecules to pass through simultaneously when open.
Steps in Facilitated Diffusion
- Carrier opens to one side.
- Solute binds to the carrier.
- Outer gate closes, occluding solute.
- Inner gate opens, allowing solute to exit into the cell.
- Carrier resets for another cycle.
Specificity in Carrier-Mediated Transport
- Carriers have specific binding sites for solutes, providing selective transport.
- Some carriers exhibit absolute specificity for particular molecules, while others can bind similar molecules or are relatively nonspecific.
Saturation in Carrier-Mediated Transport
- Limited number of carrier proteins leads to saturation when all carriers are engaged.
- After saturation, increasing solute concentration does not enhance transport rate.
Flux and Michaelis-Menten Kinetics
- Transporters with low Km values efficiently transport solutes at low concentrations.
- Flux is often regulated by the number of active carriers; e.g., insulin triggers GLUT4 incorporation into the membrane.
Concepts of Jmax (Vmax) and KM (Kt)
- Jmax (Vmax): The maximum transport rate of a solute.
- KM (Kt): Concentration at which transport rate is half of Jmax.
Comparison of Transport Mechanisms
- Simple Diffusion: Passive movement down the concentration gradient.
- Diffusion through a Channel: Passive movement via channel proteins.
- Carrier-Mediated Transport: Specific and possibly energy-dependent transport.
Solutes Requiring Carrier-Mediated Transport
- Large uncharged polar molecules (e.g., glucose, sucrose).
- Ions (e.g., H+, Na+, Cl-).
Mechanisms for Direction of Net Transport
- Uniporter & Facilitated Diffusion: Single solute transported downhill; direction depends on electrochemical potential.
Pumps in Primary Active Transport
- Often referred to as pumps, these actively transport ions (e.g., Na+ and K+) using ATP.
Importance of the Na+/K+ Pump
- Maintains high K+ and low Na+ concentrations inside cells, essential for resting membrane potential and action potentials.
- Facilitates secondary active transport and regulates cellular homeostasis.
Consequences of Na+/K+ Pump Failure
- Loss of K+ and gain of Na+ leads to cell swelling.
- Impaired cellular function, as seen in conditions like digitalis toxicity, where increased intracellular Na+ reduces Na+/Ca2+ exchange, raising intracellular Ca2+ levels.
Electroneutral vs. Electrogenic Transport Mechanisms
- Electrogenic: Contributes to membrane potential (e.g., Na+/K+ pump).
- Electroneutral: Does not significantly affect membrane potential.
Methods to Alter Na+/K+ Pump Activity
- Inhibition: Low sodium or potassium levels, use of drugs (e.g., ouabain, digitalis), limited ATP supply.
- Stimulation: Increased intracellular Na+ concentration boosts pump activity.
Secondary Active Transport Directionality
- Both solutes must be present; transport is driven by their electrochemical gradients without direct ATP involvement.
Co-transport (Synport) Mechanism
- Carrier protein binds two or more solutes simultaneously; function depends on the presence of both.
Example of Co-transport Mechanism
- Na+ and glucose reabsorption in kidney proximal tubule cells prevents glucose loss in urine.
Anti-transport Mechanism
- Requires both solutes; transport can be reversible, depending on their electrochemical gradients.
Energetics of Carrier-Mediated Transport
- Carriers are reversible, where direction is determined by net energetics based on the concentrations of solutes.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Description
Test your knowledge on carrier-mediated transport mechanisms with these flashcards. Learn the definitions and types of transport involved in the process. Perfect for anyone studying cell biology or physiology.
