Membrane and Gas Transport Flashcards
What kind of molecules can pass directly through the phospholipid bilayer?
Lipid soluble molecules
What molecules have to be transported across the phospholipid bilayer?
Charged, polar molecules or large molecules
What are the three main types of membrane transport?
Simple diffusion, facilitated diffusion, and active transport
simple diffusion
Diffusion of molecules through the cell membrane or through an open channel. Goes down the concentration gradient until system reached equilibrium.
In general, what is Fick’s law?
Fick’s law is an equation that describes the rate at which a substance can flow down its gradient. (I.e., how quickly it move from one compartment to another or how easily a solute can pass through a membrane).
What factors can influence net flux?
Electrical gradient, temperate, surface area, mass, and membrane permeability.
What kind of relationship does Fick’s law represent?
A linear relationship. As the permeability of the membrane increases, the flux increases.
Partition Coefficient
relates how well a substance will partition itself between two I miscible substances. Basically, will it stay between them or does it prefer water or lipid?
How do you calculate the partition coefficient?
Concentration of substance in oil/concentration of substance in water
Partition coefficient=1
Exists equally in water and oil
Partition coefficient>1
Lipophilic (soluble in oil) and can pass easily through the membrane.
Partition coefficient
Only soluble in water and will not easily pass through the membrane
Pore
Non gated transmembrane protein channel that is always open. Transports according to the concentration gradient.
Channel
Gates transmembrane protein that can open and close
Transporter
Transmembrane protein that undergoes a conformational change and facilitates the transport of a “packet of substrate across the membrane.
What do ion channels do?
They increase the permeability of the membrane for that ion species.
What are the three types of ion channels?
Ligand gated-activated with a specific molecules binds to the binding site causing a conformational change.
Voltage gated-a change in the membrane potential causes the molecules to move within the channel.
Mechanosensitve-whole stretch of the membrane that may affect the channel conformation by either opening or closing the channel.
What are the four major factors that determine the rate of transport across a membrane?
Saturation of transporter
Number of transports
Conformational change (takes time to change shape)
Gradient
Facilitated Diffusion
Solute is moved across a membrane down its electrochemical gradient. Transporters are specific for a substrate.
Active Transport
requires an energy source to move a solute against its electrochemical gradient (which can generate voltage). that energy source is usually ATP
what is the difference between primary active transport and secondary active transport?
In primary, the concentration gradient is used to move a solute against its own gradient, n secondary it moves another solute against its concentration gradient.
Co-transporter
In secondary active transport in which both substrates are moved in the same direction
Exchanger
In secondary active transport in which the two substrates move in opposite directions.
Anti porters
Another name for secondary active exchangers, these utilize the electrochemical gradient of one substrate to drive another substrate in the opposite direction.
What is the major role of epithelial cells?
the secretion and/or absorption of solutes and fluid, does this by setting up an osmotic gradient that water can flow down
Absorption
Movement of solutes/fluid from lumen to blood (uses eNAC)
Secretion
Movement of solutes/fluid from blood into the lumen
Apical membrane
Membrane in contact with the luminal space
Basolateral membrane
membrane in contract with the interstitium and blood
Cardiolipin
Fatty acid that is the most common component of the inner mitochondrial membrane (about 20%)
What kind of transport do the GLUT transporters utilize? Do they depend on sodium?
they do facilitated diffusion and do not rely on sodium
GLUT 1
Brain, RBC
GLUT 2
Liver kidney, beta cell, intestine
GLUT 3
Neurons, brain
GLUT 4
Muscle and fat
GLUT 5
Intestine, seminal vesicles (high affinity for fructose)
What makes the GLUT 4 transporter unique?
It is insulin dependent as insulin mobilizes its transport
Osmoles
Number of particles of solute that contribute to osmotic pressure
Osmolality
Osmosis/L
Osmolarity
Total number of solute particles/L
Tonicity
concentration of only the osmotically active particles (those that can’t penetrate the barrier)-control cell volume
Concentration
Mass of substance in a known volume
Chemical potential difference
Concentration gradient between two compartments
what are the two driving forces for water movement within the body?
Osmotic pressure (concentration of solutes within the water-water moves to area of high concentration) and hydrostatic driving forces (effect of gravity on the fluid across capillary endothelial cells)
what causes osmosis?
difference in solute concentration, causing water to flow from area of low osmolarity to high osmolarity (less solute to more solute)
How does reflection coefficient relate to osmotic pressure?
You can’t have osmotic pressure without reflection. The inability of solutes to cross the membrane is what drives the flow of water
Penetrating Solutes
can enter the cell (glucose, urea) and will distribute until equilibrium is reached
Non-penetrating solutes
Cannot enter the cell (sucrose, things that dissociate into ions) and water will move to dilute solutes
Isoosmotic
total osmotic pressure of solution=osmotic pressure of cell
Hyperosmotic
Solution has a greater osmotic pressure than the cell
Hypoosmotic
Is the solution has less osmotic pressure than the cell
Isotonic
A solution is isotonic if, at equilibrium, it causes the cell to neither shrink nor swell (non-penetrating solute concentration is equal on both sides of cell membrane)
Hypertonic
Causes cell to shrink (non-penetrating solute is greater outside the cell)
Hypotonic
Causes cell to swell (non-penetrating solute concentration is greater inside the cell than outside)
Trans cellular
Movement of water across epithelial cells
Paracellular
Movement of water between cells-determined by how “tight” or “leaky” the cells are
What determines membrane potential?
which ion has a greater conductance at rest (usually potassium) and the magnitude of the concentration gradient for the ion
When does a membrane potential result in zero net flux?
Net flux will be zero when the electrical energy is equal and opposite to the chemical energy
What is the main purpose of the Nernst equation?
It tells you the membrane potential that keeps the ions in equilibrium
What has the greatest effect upon membrane potential in a cell?
the most permeant ion has the greatest effect, so most cell membrane potentials are close to the potassium equilibrium potential (most cells have high K permeability)
Membrane potential
Potential difference between the inside and outside of the cell
Equilibrium Potential
Potential at which there is no flux of ion
