TRANSPORT MECHANISM TRANSPORT OF SUBSTANCES THROUGH THE CELL MEMBRANE
Sep 13, 2015
TRANSPORT MECHANISMTRANSPORT OF SUBSTANCES THROUGH THE CELL MEMBRANE
Approximate concentrations of electrolytes and other substances ECF: Na, Cl, Ca, HCO3, glucoseICF: K, PO4, amino acid
CELL MEMBRANELipid bilayerConstitutes a barrier against movement of water molecules (controls passage of substance in and out of the cell)Large amounts of proteins penetrating all throughout the membrane
CELL MEMBRANE TRANSPORT PROTEINSCHANNEL PROTEINSHave watery spaces all the way through the molecule ---- allows free movement of water
CARRIER PROTEINSBind with the molecules/ions that are to be transported conformational change in the protein molecules to move the substance
2 BASIC TRANSPORT PROCESSESDIFFUSION2 subtypes: 1. Simple Diffusion 2. Facilitated Diffusion
ACTIVE TRANSPORT
DIFFUSIONRandom molecular movement of substances molecule by molecule either thru:Intermolecular spaces in the membraneCarrier proteinRate is to the concentration difference
Energy that causes diffusion: normal kinetic motion of matter
molecules are in constant motion
SIMPLE DIFFUSIONKinetic movement of molecules occurring thru a membrane opening or intermolecular spaces WITHOUT any interaction with carrier proteins
SUBTYPES OF DIFFUSION
Simple diffusionThrough the interstices of lipid bilayer
Through watery channels
FACTORS AFFECTING THE RATE OF DIFFUSIONAmount of substance available
Velocity of kinetic motion
3. Number and sizes of openings in the membrane
SUBTYPES OF DIFFUSIONFACILITATEDDIFFUSIONrequires interaction of a carrier proteinAid in the passage of molecules by binding chemically with them
FACILITATED DIFFUSIONA.k.a carrier-mediated diffusion
Substances transported diffuses thru membrane using a specific carrier protein
FACILITATED DIFFUSIONImportant substance that crosses cell membrane: glucose and amino acids
DIFFERENCE B/W SIMPLE AND FACILITATED DIFFUSION:Simple Diffusion- rate of diffusion increases proportionately with concentration of diffusing substances
Facilitated Diffusion- rate of diffusion approaches a maximum (Vmax) as the concentration of substances increases
DIFFUSION OF LIPID SOLUBLE SUBSTANCES THRU LIPID BILAYERLipid solubility one of the most important factor that will determine the rapidity of substance diffused
Directly proportional to its lipid solubility
Oxygen, Nitrogen, CO2, alcoholDissolve directly in the lipid bilayerHigh lipid solubility
DIFFUSION OF WATER /LIPID INSOLUBLE THRU PROTEIN CHANNELS
Water is insoluble in lipid membrane but readily passes all the way through the channel proteins
GATING OF PROTEIN CHANNELSProvide a means of controlling ion permeability of the channelsTWO WAYS
1. VOLTAGE GATING
2. CHEMICAL (Ligand) GATING
VOLTAGE GATINGResponds to the electrical potential of the membrane
VOLTAGE GATINGStrong (-) charge on the inside of the cell membrane
outside Na gates closed tightly
VOLTAGE GATINGMembrane loses its (-) charge inside
Na gates open
Allows Na to pass inward the membraneBasic mechanism in eliciting an action potential
VOLTAGE GATINGK channels in the intracellular ends
opens when inside becomes (+) charge
Responsible for terminating an action potential
CHEMICAL (LIGAND) GATINGOpened by the binding of a chemical substance with protein
Causes a conformational change in protein molecule that either closes or opens gate
E.g acetylcholine (nerve transmission)
ACTIVE TRANSPORTCell membrane moves an ion against a concentration, electrical, chemical gradientMovement of ions/molecules across a membrane in combination with a carrier protein Additional source of energyE.g Na, Ca, K, Hydrogen
TYPES OF ACTIVE TRANSPORTPRIMARY ACTIVE TRANSPORTNa-K pumpCaHydrogenSECONDARY ACTIVE TRANSPORTCo transportCounter transport
PRIMARY ACTIVE TRANSPORT
Energy is derived directly from the breakdown of ATP
Na-K pumpTransport process that pumps Na out thru the cell membrane at the same time pumping K ions to the inside of the cell
Responsible for maintaining Na & K difference across cell membrane
Controls the volume of each cell (swell or shrink)
Na-K pumpBasis of nerve function, transmitting nerve signals throughout the nervous system3 specific features for Pump functioning:3 receptor sites for binding Na ions2 receptor sites for K on the outsideHas ATPase activity binding sites
2 K ions outside & 3 Na inside of carrier protein
ATPase activated
cleaves 1 molecule of ATP
splitting it to ADP
liberates high energy PO4 bond
chemical & conformational change in the protein
Na outside K inside
PRIMARY ACTIVE TRANSPORT OF CALCIUMCalcium ions normally maintained at a low concentration in the intracellular cytosol
In the intracellular vesicular organelles (sarcoplasmic reticulum) of muscle cells and mitochondria
PRIMARY ACTIVE TRANSPORT OF HYDROGEN IONS
Important inGastric glands of the stomachLate distal tubules and cortical collecting ducts of the kidneys
SECONDARY ACTIVE TRANSPORTEnergy derived secondarily from energy that has been stored in the form of ionic concentration difference of secondary molecule between two sides of the membraneCo-transport and counter transport
CO-TRANSPORTDiffusion energy of Na can pull along other substances thru the cell membraneCoupling mechanism required by means of a carrier protein attachment point for both Na & subs transported inside the cell
COUNTER-TRANSPORTNa attempts to diffuse to the interior of the cell; other substance is inside the cell
Na binds to carrier protein projects to exterior; other substance binds causing it to move
OSMOSISProcess of net movement of water caused by a concentration difference of waterPassive movement of water across a selectively permeable membraneDriving force: osmotic pressure differenceMost abundant substance that diffuses across membrane ---- waterIn certain conditions ---- concentration difference of water develops ---- cell would swell or shrink
OSMOTIC PRESSURE- exact amount of pressure required to stop osmosis- dependent on the number of particles per unit volume of fluid
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