Membrane Transport Flashcards
2 properties that influence whether a particle can permeate a plasma membrane without assistance?
Size of the particle
Permeability of the molecule in lipid
What is required for movement across a membrane?
A pathway and a driving force
Types of driving forces?
Passive
Active- requires cell to expend ATP
What must a substance be, for a membrane to be permeable to it in passive diffusion?
Small, lipid soluble molecule
There also must be a concentration gradient
Factors in Fick’s law of diffusion?
1) Magnitude of concentration gradient
2) Surface are of membrane across which the diffusion is happening
3) Lipid solubility of the substance
4) Molecular weight of the substance
5) Distance through which diffusion must take place
As molecular weight increases, rate of diffusion..?
Decreases
Effect of an Increased concentration gradient on Fick’s law rate of net diffusion?
Increases it
Effect of an increased SA of membrane on the rate of net diffusion according to Fick’s Law?
Increases it
Effect of Increasing Lipid solubility on rate of net diffusion across a membrane according to Fick’s law?
Increases net diffusion
Effect of increasing molecular weight on rate of net diffusion across a membrane according to Fick’s law?
Decreases rate
Effect of increasing thickness of membrane on rate of net diffusion according to Fick’s law?
Decrease rate
Symbols for Conc gradient SA of membrane Lipid solubility Molecular Weight Thickness of membrane
(Triangle )C A B MW (Triangle) X
Fick’s Equation
Q∝ △C . A . P
Types of ion specific channel proteins?
Ligand-Gated or leak
How an Electrochemical Gradient is produced?
Difference in charge between two adjacent areas generates an electrical gradient
What does an electrochemical gradient promote?
Movement of ions towards areas of opposite charge
Electrochemical Gradient Definition
The net effect of electrical and concentration gradients on an ion.
Definition of Diffusion
The net diffusion of water down it’s own concentration gradient through a selectively permeable membrane
Where does water move to in osmosis?
Area of higher solute concentration
Osmolarity
Concentration of osmatically active particles present in a solution
Tonicity
Effect a solution has on cell volume
Units of tonicity?
NO UNITS
Ways to describe a solution
Isotonic
Hypertonic
Hypotonic
Units of osmolarity?
Osmoles of solute per litre (Osm/l)
Normal cell volume?
Intracellular Fluid= 300mOsm
2 different mechanisms for selective transport?
Carrier-mediated transport
Vesicular transport
Passive transport mechanisms?
Simple diffusion (down a conc gradient) Movement along electrical gradients (Ion channels) Osmosis
What do all passive transport mechanisms depend on?
Lipid solubility of molecule
or
Ability to fit through specific ion channels
3 important characteristics of carrier-mediated transport?
Specifity
Saturation
Competition
Comparing transport rates between a carrier mediated transport & simple diffusion down a concentration gradient.
- Simple diffusion gets a higher rate of transport of molecule into the cell but a lower concentration of transported molecules in the ECF than Carrier mediated transport
- Facilitated diffusion has a lower rate of transport of molecule into cell however reaches a higher concentration of transported molecules in the ECF
2 forms of carrier mediated transport?
Facilitated diffusion
Active Transport
Facilitated Diffusion definition?
Uses a carrier protein to facilitate the transfer of a substance across a membrane ‘downhill’ from high to low concentration
Active Transport Definition?
Requires the carrier to expend energy to transfer a substance ‘uphill’ across a membrane against a concentration gradient
Two forms of Active transport?
Primary
Secondary
Primary AT?
Energy is directly required to move a substance against it’s concentration gradient
Secondary AT?
Energy is required, but it is not used directly to produce ‘uphill’ movement.
The carrier does not split ATP – instead it moves a molecule ‘uphill’ by using secondhand energy stored in the form of an ion concentration gradient (usually a Na+ gradient)
What is a Na+/K+ pump?
More complicated Primary active transporter
Where is a sodium/Potassium pump found?
Plasma membrane of all cells
3 important roles of Na+/K+ Pump?
- Helps establish Na+/K+ concentration gradients across plasma membrane of all cells
- Helps regulate cell volume by controlling concentration of solutes inside cell
- Energy used to drive the pump indirectly serves as the energy source for secondary AT.
Secondary AT definition
The transfer of a solute across the membrane is always coupled with the transfer of the ion that supplies the driving force (typically Na+)
2 mechanisms which 2AT could occur by?
Symport or Antiport
Symport
Solute and Na+ move in same direction
Why does Vesicular transport need energy?
Vesicular formation and movement within the cell
Endocytosis?
Pinching off of membrane to engulf substance
or
extracellular environment engulfed into intracellular environment
Exocytosis
A vesicle fuses with the plasma membrane, releasing its contents to the ECF
