Chapter 5 & 6 Membrane Dynamics Flashcards
What are the properties of the plasma membrane?
It separates the ECF and the ICF
It’s selectively permeable - meaning it only allows certain things through.
Most charged molecules do not get across
Many lipid-soluble molecules can easily get across
What are the three properties given in class on whether a molecule will make it past the membrane?
Lipid solubility
Charge
Size
How does non-carrier mediated transport take place? What makes it go?
What is the technical name for this?
Driven by concentration forces
Passive diffusion
Define passive diffusion
The movement of molecules or ions down their electrochemical gradient.
Lipid soluble and gases get across easily
What moves substances until the electrochemical forces acting on the permeant substance sum to what?
Diffusional forces- move substances until the electrochemical forces acting on the permeant substances sum to ZERO
Even though the electrochemical forces and the permeant substances have sum to ZERO what is taking place?
Movement is still occurring
But net diffusion = 0
In non-carrier transport, what is the rate of diffusion of a compound depends on what?
Magnitude of its concentration gradient Permeability of the membrane Temperature Surface area of the membrane Thickness of the membrane
Passive diffusion of water is referred to as what?
Define it?
Osmosis
Diffusion of water across a selectively permeable membrane
What causes osmosis?
Driven by osmotically active substances which are NON-penetrating solutes
What is Osmotic pressure?
The force or pressure that must be applied to oppose osmosis.
what is facilitated diffusion?
What is the difference from non-carrier and facilitated diffusion?
Diffusion of molecules or ions that do not easily cross the membrane
Just like passive diffusion but via ion channels or carrier proteins
What are the types of channel proteins involved in facilitated diffusion?
Open channels- like pores
Gated channels
How does carrier proteins function?
What are the three types of carrier proteins?
They open to only one side at a time either ECF or ICF, then that specific end will close and then open to the opposite side
Uniport- only moves one type of substrate
Symport - move two or more substrates in the same direction. E.g Na+ and Glu.
Antiport- moves substrates in the opposite direction. Ex. 3Na+ out of the cell and 2K+ into the cell.
Define Active Transport? What is the most common antiport transporter and what does it move across the membrane?
What does the transport mechanism use to transport things across?
What is taking place
Active Transport: needs energy in the form of ATP to transport substrates across the membrane
Transport mechanism is membrane bound proteins
Movement is agains the concentration gradient
What are the properties of Carrier Proteins? What do they exhibit?
Specificity
Saturation. Tm (transport maximum)
Competition
Transport rate is proportional to what?
Transport rate is proportional to substrate concentration until the carriers are saturated
In Primary Active Transport what does the ion pumps need and what is its purpose?
Ion pumps use 25% of the ATP that the cell has made
This maintains the concentration gradients coupled to the movement of solutes
The Na+/K+ pump does what for the cell and what type of transport is this?
Moves 3 Na+ out of the cell and 2K+ into the cell
This takes ATP because its moving against its concentration gradient
This is primary active transport
What is another type of carrier mediated transport that doesn’t directly use ATP to move substrates against their electrochemical gradient?
Give an example
Secondary Active Transport
Glucose moves into the cell
As Na+ flows into the cell passively energy is released, which facilitates glucose transport
What are the two types of transport across epithelial membranes?
Transcellular transport- moves it through the cell through separate mechanisms at the apical and basolateral membranes
Paracellular Transport- moves spaces through the tiny spaces between the cells
Basolateral faces what?
Apical membrane faces what?
ECF
Apical membrane faces the Lumen
What is transport across epithelial cell layers opposed?
The lipid bilayer is an effective barrier
The junctional complexes linking adjacent cells can limit transport
What are the three junctional complexes of paracellular transport?
Tight Junction- act as barriers to minimize the unregulated diffusion of material between the cells
Adherens junction- membranes are glued together by proteins that pass through both membranes and attach to cytoskeletons
Desmossomes- proteins button tow membranes together
Movement of water across the plasma membrane affects what?
Affects the cell volume
What is Osmosis?
Passive movement of water from low concentration to high concentration of solution
What drives water movement across membranes
Osmotically active substances drive H2O movement across membranes
-water moves from high water[ ] to low water [ ]
What is the magnitude of the driving force called?
Osmotic pressure
Define osmotic pressure?
The force that would have to be exerted to oppose the water movement form one compartment to the other
- The stronger the osmotic pressure = the greater force water attempting to move across the membrane
- this is also proportional to solute concentrations on both sides of a membrane
What are the units of Osmolality?
How do you define Osmolality of electrolytes that ionize in water?
Moles of osmotically active substances per Kg of water
1 mol of NaCl dissolved in water yields 1 mol of Na+ and one mole of Cl- which = 2 Osm/Kg
What is the Osmolality of blood plasma?
How is this regulated
~ 290 mOsm/kg
Homeostatically regulated
What is Tonicity?
What are the three types of solutions?
What is this term in reference to?
Tonicity refers to the effect that an osmotically active solution has on cell volume
Isotonic solutions- if the cell in the solution does not change size at equilibrium
Hypertonic solutions- if the cell loses water and shrinks at equilibrium
Hypotonic solutions- if the cell in solution gains water at equilibrium
This term is used to describe a solution relative to intracellular fluid
Define membrane Potential?
Refers to a difference in charge across the membrane
Results from selective ion movement across the membrane
Define Equilibrium Potential
If inside of cell has 100mM KCl and the outside is 10mM KCl, if the membrane is only permeable to K+ the K+ is going to leave the cell and the Cl- remains in the cell this is separation of charge
At some point, the forces will be equal in magnitude, but opposite in vectorial direction.
= Equilibrium Potential
What does the Nernst equation predict?
Predict the equilibrium potential of the permeant ion concentrations inside and outside of the cell.
Only one ion in the Nernst
What is the Resting membrane potential of most cells?
What determines the RMP
-65 to -85 mV
Determinants: [ ]’s of ions inside and out
Which ion has the highest permeability in a cell and why?
K+ permeability is the greatest, approximately 30 to 100 times that for Na+
What type of junction allows for signals to pass directly from one cell to the next?
Gap jxn- form direct cytoplasmic connections between the adjacent cells.
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