Download - Transportation across cell membrane
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TRANSPORTATION ACROSS CELL MEMBRANE
Dr.S.Harshad
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• Cell volume and composition of ICF maintained irrespective of changes in volume and concentration in Extracellular environment by transfer of substances across cell membrane
• Broadly classified into1. Direct passage without involvement of carrier
molecules2. Passage thru channels or carrier proteins
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ClassificationPassive Transports
Simple diffusionFacilitated diffusionOsmosisFiltration , Bulk Flow & Solvent drag
Active Transports
Primary active transport Secondary active transport
Vesicular Transports
ExocytosisEndocytosisTranscytosis
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Passive transports
• Features:1. Transport is downhill2. Does not require energySimple diffusion:• Random movement of molecules.• Molecules move from the area of higher
concentration to area of lower concentration.• Occurs until diffusion equilibrium is achieved.
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• Factors that determine the rate of diffusiona) Properties of the substanceb) Properties of the membrane
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Properties of substance
• Concentration and electrical gradients of substance• Permeability of substance thru membraneI. Lipid solubilityII. Molecular sizeIII. Charge on the moleculeIV. TemperatureV. Distribution of channels in membraneVI. Pressure gradient
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Properties of membrane• Surface area• Thickness of membrane• FICK’S LAW OF DIFFUSION:Net rate of diffusion (J)= -DA . Ci-Co TD- diffusion constantA- surface areaT- thickness of membrane Ci- concentration of substance inside the cellCo- Concentration of substance outside the cell.
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Facilitated diffusion
• aka carrier mediated diffusion• Features:1. Faster rate of transport2. Saturation kinetics3. Competitive inhibition4. Specificity
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Osmosis
• Process of movement of solvent from low solute concentration to high solute concentration through semipermeable membrane.
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Filtration, Bulk Flow & Solvent Drag
• Filtration is defined as the process by which fluid is forced through a membrane because of the difference in pressures on two sides.
• When filtration results in movement of greater quantity of water- bulk flow.
• During bulk flow, it carries dissolved particles along with it- solvent drag.
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Active transports• Active transport is the transport of
substances from a region of lower concentration to higher concentration using energy, usually in the form
of ATP.
• Types1. Primary active transport2. Secondary active transport
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Primary active transport
• Operated by ion pumps• Solute is transported against its
electrochemical gradient with the use of energy.
• Energy is derived from ATP
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Pumps involved in active transport
1.Sodium-potassium pump• Found in many cells
2.Calcium pump• Found in membrane of Sarcoplasmic reticulum 3.Potassium hydrogen pump• Found in Gastrointestine cell membrane
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Secondary active transport
• Transfer of one solute against its concentration gradient by using the energy generated by gradient of another solute.
• The transport may be o In the same direction (symport)o In the opposite direction (antiport)
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Vesicular Transport
• The transport process that occurs by either fusion of vesicle or formation of vesicle.
Types:Endocytosis Exocytosis
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Endocytosis
• Substance is taken into the cell by means of vesicle formation.
• The size of the vesicle varies from 0.1um to 2um
• Types:1. Phagocytosis2. Receptor mediated endocytosis3. Pinocytosis
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Phagocytosis• aka Cell Eating• Ingestion of large particles or microorganisms• Vesicles vary from 1-2 um in diameter• Neutrophils, monocytes, macrophages are
phagocytic cells.
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Receptor mediated endocytosis
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Pinocytosis
• aka Cell Drinking• Fluid phase endocytosis• Substances in extracellular fluid are
internalized to the cell.
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Exocytosis
• Export from the cell• Vesicles move to the cell surface, fuse with cell
membrane and release the content.
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Transcytosis/ Cytopemisis
• Vesicular transport limited within the cell• Vesicles are formed within the cell and
transported into the cytoplasm.
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Thank you…