Membrane transport Flashcards
How does compartmentalization affect the cellular environment?
Having membranes blocks free diffusion, which creates different properties inside the cell vs the outside
What creates the boundaries between body regions in animals to compartmentalize them?
Epithelia
What are the two surfaces on an epithelial cell?
Apical, which faces a cavity, and basolateral, which faces another cell
What is the basement membrane?
Permeable extracellular matrix that is between blood vessels and the epithelium
What are the two types of membrane proteins?
Integral and peripheral
What is an integral membrane protein?
Membrane protein that goes into the membrane
What is a peripheral membrane protein?
Membrane protein that is associated with but not in the membrane
What are the 4 types of junctions?
Tight, septate, desmosome, gap
What are the two types of occluding junctions?
Tight (vertebrates) and septate (invertebrates)
What is the function of a desmosome?
Maintain very tight contact between cells
What is the function of a gap junction?
Communication through pores between the cytoplasm of two cells
What are the two paths that a molecule can take to get across the epithelium?
Transcellular and paracellular
What is the transcellular path?
The molecule goes through the membrane, into the cell, then back out through the membrane. Used by large molecules
What is the paracellular path?
The molecule squeezes through the junction. Used for things like water and ions
What is the bulk solution?
The portion of the solution not in contact with the membrane
What is simple diffusion?
Solutes move down their concentration gradient, no energy input or carrier required
What is osmosis?
Simple diffusion of water
What does the Fick equation tell us?
The rate of diffusion
What is the purpose of a boundary layer? What animals have one?
Slows the diffusion of solutes from the animals into the environment. Seen in aquatic animals
What is the electrical gradient of the cell?
The inside of the cell is negative, outside is positive
How is diffusion affected when the solute is going down both its concentration and electrical gradient?
It goes fast
What is the Donnan equilibrium?
The balance of both the electrical and concentration gradients on both sides of the cell membrane
What is facilitated diffusion?
The solute goes down its concentration gradient, no energy input, but needs a transport protein to get across the membrane
What are the 4 ways ion channels are regulated?
Voltage, mechanical, phosphorylation, ligand binding
What is a permease?
A transport protein that isn’t a channel
What is a porin?
Large channels that let bigger molecules through
What does the Na+/glucose symporter do? Which membrane in an intestinal epithelial cell is it found on?
Brings one Na+ (down gradient) and one glucose (against gradient) into the cell. Found on the apical membrane
What does the Na+/H+ antiporter do?
Moves one Na+ into the cell and one H+ out
What causes a voltage gated ion channel to open?
A change in voltage, when the membrane potential becomes negative on the outside and positive on the inside (aka action potential)
What causes a phosphorylation gated ion channel to open?
Phosphorylation
What causes a mechanically gated ion channel to open?
Physical stretching of the membrane
What causes a ligand gated ion channel to open?
Ligand binding to a receptor
What does the Na+/K+ ATPase do?
Maintains the electrochemical gradient of ions by using active transport to pump 3 Na+ out of the cell and K+ into the cell (both against their concentration gradients)
What causes the confromational change in the Na+/K+ ATPase?
ATP hydrolysis
What is membrane potential?
Difference of electrical charges across the cell membrane
Which membrane is the Na+/K+ ATPase on in intestinal epithelial cells?
Basolateral
How is glucose transported across the intestinal epithelium?
Enters through the Na+/glucose symport (secondary active transport), moves through the cell and out through a glucose transporter on the basolateral membrane (facilitated diffusion). Uses the gradient built by the Na+/K+ ATPase on the basolateral membrane
