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CYTOGENETICS
Lesson
[TRANS] LESSON 3: CELL MEMBRANE TRANSPORT
CELL MEMBRANE TRANSPORT
ROLE OF MEMBRANE PROTEINS
โ Proteins act as passages for solutes โ (A) Liposome - protein free, artificial lipid bilayer โ (B) Cell membrane โ Solutes โ main thing that passes through the membrane proteins
PERMEABILITY OF SOLUTES
โ Small, nonpolar molecules โ Dissolved readily โ Steroid hormones pass easily because they are derivatives of cholesterol โ Uncharged polar molecules โ Diffuse readily โ Dependent on size โ Charged molecules โ Cannot pass through (positively & negatively charged ions)
CHARGED ION CONCENTRATIONS IN THE CELL
โ There are different charged ion in the cell: โ Some are increased intracellularly โ meaning they have high concentration inside the cell โ Potassium โ main intracellular cation, high concentration outside โ Some are increased extracellularly โ meaning they have high concentration outside the cell โ Sodium โ main extracellular cation, high concentration outside the cell โ Most anions are found in the extracellular matrix (outside the cell) โ Chlorine โ main extracellular anion โ Negatively charged
MEMBRANE POTENTIAL
โ Voltage difference across the cell membrane caused by an imbalance of charged molecules โ Resting membrane potential โ -20 and -200 millivolts (mV) โ Uses: โ Transport of certain metabolites โ Using gradient transport โ Example: Neurons โ Cell-cell communication
CLASSES OF MEMBRANE TRANSPORT PROTEINS
CHANNEL
โ Uses size and electric charge โ Non-selective
TRANSPORTER
โ Uses binding sites โ Selective
TYPES OF TRANSPORT
(1) PASSIVE TRANSPORT
โ The concentration gradient is dictating the movement of the solutes
LESSON 3: CELL ORGANIZATION โ Goes to the more concentrated to the less concentrated โ Happens naturally, no need to extend energy โ Two types of transport proteins: โ (1) Channel-mediated โ Hole inside cell membrane โ Uses its size & electrical charge โ Non-selective โ (2) Transport-mediated โ Uses binding sites โ Specific passive transport โ Selective
(2) ACTIVE TRANSPORT
โ The movement of ions or molecules across a
cell membrane into a region of higher
concentration, assisted by enzymes and uses
energy.
โ Pumps โ active transporters
CONCENTRATION GRADIENT
โ Factor in play during transport
โ The gradual difference in concentration of a
dissolved substance in a solution between a
region of high density and one of lower density
ELECTROCHEMICAL GRADIENT
โ Net driving force of passive transport โ These two gradients are combined: โ Concentration gradient โ Membrane potential
OSMOSIS
โ A process by which molecules of a solvent tend
to pass through a semipermeable membrane
from a less concentrated solution into a more
concentrated one, thus equalizing the
concentrations on each side of the membrane.
โ Aquaporins (AQP) โ serve as channel in
the transfer of water across a membrane
COMBATTING OSMOTIC SWELLING
โ (A) Protozoan โ keeps water in a vacuole and expels it outwards in a discharging contractile vacuole โ (B) Plant Cell โ welcomes water because of cell wall for the intracellular pressure called turgor โ (C) Animal Cell โ they donโt have cell wall, so they release ions & water accordingly
ION CHANNELS
โ Characteristics: โ Ion selectivity โ Gated
PASSIVE TRANSPORTERS
โ Moves a solute along its electrochemical gradient โ Two types of Glucose: D & L Glucose โ Binds only D Glucose
