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

THANK YOU