Ch 9 Membrane Transport Flashcards
What are the two general modes of passage across the membrane?
Passive and Active.
Define passive transport.
Solutes diffuse across the membrane according to their concentration gradient without requiring an input of energy.
What type of solutes do not require a transporter protein for passive transport?
Some small nonpolar solutes (e.g., steroid hormone).
What do polar and charged solutes require for passive transport?
A protein transporter.
What is active transport?
It pumps solute across the membrane against the concentration gradient.
What does active transport always require?
A transporter protein and an input of energy.
What is simple diffusion?
Solute diffuses directly through the bilayer or through a static protein channel.
What is facilitated diffusion?
Passive transport where solutes are moved across the membrane by proteins.
How does facilitated diffusion work?
The solute binds to a membrane protein, which changes shape to release the solute on the other side.
What are aquaporins?
Water-specific pores that allow only water molecules to pass through.
Where are mammalian aquaporins expressed at high levels?
In tissues where fluid transport is important, such as the kidney, salivary glands, and tear glands.
What characterizes the E. coli OmpF porin?
It is a trimer that forms a β barrel with a water-filled core for transmembrane movement of ions or molecules.
What is the selectivity filter of the K+ channel?
It is about 10,000 times more permeant to K+ than to Na+.
What is the role of the Na,K-ATPase?
It maintains the concentration gradients of Na+ and K+ across the cell membrane.
What is primary active transport?
It builds up concentration gradients using energy from ATP hydrolysis.
What is secondary active transport?
It uses an existing concentration gradient established by another pump.
What is the action potential?
A rapid change in membrane potential due to Na+ influx when a nerve is stimulated.
How does myelination affect action potential propagation?
It allows action potentials to propagate rapidly by insulating axons.
What is the membrane potential?
The voltage across a membrane caused by ion transport.
What is the formula for calculating free energy change for transmembrane movement?
ΔG = RT ln([X]inside/[X]outside) + ZFΔψ.
What is the purpose of the electron transport chain?
To transport protons (H+) from the matrix across the inner membrane of the mitochondria.
What is the result of the proton gradient created by the electron transport chain?
It provides the energy for phosphorylating ADP to ATP.
What drives the active transport of H+ in the electron transport chain?
Electron transfer steps from NADH to O2.
What is the relationship between Na+ and K+ concentrations inside and outside cells?
Na+ concentrations are much lower inside the cell, while K+ concentrations are much higher inside.
True or False: Active transport is unidirectional.
True.
Fill in the blank: The inward movement of Na+ during an action potential makes the membrane potential more _______.
positive.
