Exam2: Membrane Transport, Membrane Potential, & Biolelectricity Flashcards
Cell Membrane is a Barrier
Cell Membrane Barier
Seperates inside of cell from outise fluid
* Inside = cytosol = intracellular
* Outside - extracellular = interstitial
Allows inside concentration of electrolytes and other sollultes to be different from extracellular concentration of solutes
* Higher Inside: Proteins (negativley charged) and K^+
* Higher Outside: NA^+ , CL^-, and ca^2+
Permeability
Cellular Permeability
The ease with which subtsances can cross the cell membrane
* Nothing can pass through an impermiable layer
* Anything can pass through a freeley permeabile barrier
* Cell membranes are Selectivley Permeable
Transport Mechanisms
Cellular Transport Mechanisms
- Passive = cell does not expend energy
- Active = cell expends energy
- Diffusion (chanel proteins) = in a solution or across a membrane
- Pasive
- Random motion of ions and molecules down their concentration gradient
- Carrier Mediated Transport (across membrane)
- Pasive or active
- Requires transport protein in membrane
Diffusion
Cellular Diffusion
Movement of a substance from an area of high concentration to low concentration
* Molecules with no eletrical charge = diffuse down or along the chemical concentration gradient of the molecule
* For charged ions and molecules
* Diffuse based on electro-chemical gradient
* Chemical Concentration is one driving force
* Electrical concentration gradient is another driving force
Diffusion
Diffusion in Body Fluids
Examples:
* O2 moves from lungs into blood, into interstitial spaces, into cells, into mitochondria
* CO2 moves from cells into interstitial spaces, into blood, out through lungs
* Water moves across epithelium of digestive tract into body tissues
Diffusion
Diffusion across cell membranes
Membrane must be permeable to the substance for diffusion to occur
Lipid bilayer portion of cell membranes:
* Permiable to O2, CO2 and most hydrophobic molecules
* NOT permiable to most large molecules and most hydrophilic molecules
Membrane proteins can provide channels for passive diffusion
Osmosis
Osmosis
- Diffusion of water across a semipermeable membrane in response to solute differences
- Concentration of water is related to total concentration of all solutes (disolved materials) including ions, proteins, monomers, polymers, etc…
- Water moves by diffusion down its concentration gradient
Osmosis
Osmosis
- Water tends to diffuse across a membrane toward solution contaning the higher solute concentration
- Osmotic Pressure = force of water movement into a solution
Tonicity
Tonicity
Tonicity = the effects of extracellular solutions on cells
* Isotonic = no net osmosis, not net gain or loss of water
* Hypotonic = net gain of water into cell. Can result in cytolysis (hemolysis in RBCs)
* Hypertonic = net water flow out of cell. Can result in crentaion
Tonicity
Tonicity
- Hypotonic = extracellular solution - less solutes, more water than intracellular solution - water will flow into cell
- Hypertonic = extracellular solution - more solutes, less water than intracellular solution - water will flow out of cell
Diffusion
Factors Influencing Diffusion
- Distance - concentration gradients effective only over short distances, few cells are more than 125 picomemters from a blood vessel
Diffusion is faster if:
* Molecule is smaller
* Tempature is higher
* Concentration gradient is higher
Charged ions or molecules
- For charged ions, concentration gradient is one driving force, eletrical gradient is another driving force
Transport Mechanisms
Transport Mechanisms
Diffusion (in a solution or across a memrbane
* Passive process (no energy required)
* Random motion of substace down their chemical or eletrical concentration gradient
Carrier mediated transport (across membrane)
* Pasive (no energy required) or active (Energy required)
* Requires transport protien in membrane
Carrier Mediated Transport
Carrier mediated Transport
Membrane protiens bind and transport spesific molecules or ions
* Specifity - carrier proteins are generally spesificaly for a particular substance
* Saturation Limits - rate of transport subject to number of transport proteins available
* Regulation - various control factors exist that affect activity of carrier proteins
Carrier Mediated Transport
Carrier Mediated Transport
Many carrier proteins transport one substance, one way only
Some carrier protiens transport two substances at same time
* Cotransport - both go same directions across membrane
* Counter-transport - go opposite directions across membrane
Facilitated Diffusion - passive
Active Transport - active
Facilitated Diffusion
Facilitated Diffusion (across a membrane)
Substance moves down conc. gradient
* Energy is supplied by concentration gradient, no ATP needed
Requires transport protien
* Different transport proteins for different substances
Differs from simple diffusion
* Maximum rate is dependent on avaliability of transport protein - can reach saturation
Facilitated Diffusion
Facilitated Diffusion with co-transport against concentration gradient
One substance move down its conc. gradient
* Energy is supplied by concentration gradient, no ATP is required
Another substance moves against its concentration gradient
* Energy is supplied by concnetration gradient of other substances Requires ATP
* 3 NA out 2K in
Active Transport
Active Transport across a membrane
Active transport
* Consumes ATP
* Independent of concentration gradient
Examples of active transport include:
* Ion Pumps
* Secondary Active transport
