Lecture Two Flashcards
What are phospholipids?
Amphipathic
Why are phospholipids amphipathic
Because they have a hydrophilic head group and hydrophobic tail groups
At low concentrations what will phospholipids form what shape in water
Monolayer
At high concentration phospholipids will form what shape in water
Micelles and eventually a bilayer
Which way can phospholipids move
Laterally, rotate or flex
Which way can’t phospholipids move
Flip from leaflets
What does cholesterol do
Aids in stiffening the membrane
What can cholesterol in the membrane do
Flip back and fourth easily
What is the purpose of phospholipids
Form a barrier against diffusion
Why do phospholipids form a barrier against diffusion
To control concentration of ion flow in and out of the cell
What is the movement from one location to another as a result of random thermal movement
Diffusion
What does this formula represent
Jx=Px([X]o-[X]i)
Simple diffusion and ficks law
What does Jx represent
Flux of solute
What does Px represent
Permeability coefficient
When does ficks law work
Uncharged solutes
What is the driving force that determines the passive transport of solutes across a membrane
Electrochemical gradient
What is the unidirectional equation
Flux in - flux out
What contributes to the movement of X
Concentration of X is higher out than in
If concentration of X is charged then electrical potential out does not equal in
What happens when no net driving force is acting on X
X is at equilibrium across the membrane and no net transport of x across membrane
What does membrane transport depend on?
Presence of integral proteins
What happens in the absence of integral proteins
Cell membrane is practically impermeable to ions and water molecules
What are the two ways membrane transport occurs
Actively or passively
What are pores
Channels that are always open “leak channels”
What are channels
Pathways that can be opened or closed
What are carriers
Things that facilitate passive transport through membrane
What are water pores
Pathways that provide aqueous transmembrane conduit and is always open
What are porins
a substance in outer membranes of gram negative bacteria an mitochondria
What is perforin
Cytotoxic t lymphocytes that kill their target cell
Nuclear pore complex
Regulates traffic in and out of cells
What are aquaporins (aqp)
Channels just large enough to allow water molecules to pass through
What are channels
Gated pores formed by polypeptide subunits
