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Transport through cell membrane



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Transport through cell membrane

  1. 1. Edited by Dr Dina Merzeban physiology lecturer Fayoum university
  2. 2.  It consists of the phospholipid bilayer with embedded proteins.  selectively permeable to ions and organic molecules  controls the movement of substances in and out of cells.  protect the cell from its surroundings. CELL MEMBRANE
  3. 3. Transport through cell membrane  Passive transport or diffusion  Active transport
  4. 4. PASSIVE TRANSPORT or DIFFUSION:  Molecules move down their concentration gradient.  Molecules reach an equilibrium where they are evenly distributed.  PASSIVE
  5. 5. Simple diffusion It is further devided into:  1- Simple diffusion through lipid layer  2- Simple diffusion through protein layer  3- Facilitated or carrier- mediated diffusion
  6. 6. SIMPLE DIFFUSION THROUGH LIPID BILAYER •  Lipid layer of the cell membrane is permeable to lipid soluble substances  The diffusion through lipid layer is directly proportional to the solubility. 1. Oxygen, Carbon dioxide – Non-polar. 2. Water – Polar but very small-high kinetic energy
  7. 7. SIMPLE DIFFUSION THROUGH PROTEIN LAYER  Proteins form channels for diffusion of water soluble substan  They are either Ungated channels or Gated channels. Gated channels: 1- Voltage-gated channels. 2 Ligand-gated channels. 3 Mechanically gated channels.
  8. 8. FACILITATED DIFFUSION:  Large polar molecules such as glucose and amino acids  PASSIVE  With concentration gradient
  9. 9. FACTORS THAT DETERMINE THE RATE OF DIFFUSION: 1.The steepness of the concentration gradient. 2.Temperature. 3.Solubility of the substance. 4.permeability of the cell membrane. 5.Thickness of the cell membrane 6.Size of the molecule. 7.Size of the ions. 8.Charge of the ions.
  10. 10. OSMOSIS The passive movement of solvent molecules through a semi-permeable membrane(permeable to water and impermeable to solutes) into a region of higher solute concentration.
  11. 11. OSMOTIC PRESSURE  Osmotic pressure is the pressure created by solutes in a fluid during osmosis.  The external pressure required to prevent osmosis  Osmotic pressure is a colligative property: It means that, osmotic pressure depends upon the molar concentration of the solute but not on the identity.
  12. 12. ONCOTIC PRESSURE OR COLLOIDAL OSMOTIC PRESSURE:  Is the part of the osmotic pressure created by the larger colloidal substances particularly protein .  Albumin creates 70% of oncotic pressure. Normal oncotic pressure is about 25mm hg.
  13. 13. Importance of osmotic pressure: 1- Fluid Balance 2- Blood volume (osmosis significantly contributes to the regulation of blood volume and urine excretion). 3- Transfusion (isotonic solution of NACL or glucose are commonly used in i/v transfusion in hospital for treatment of dehydration, burns etc).
  14. 14. SUBSTANCES TRANSPORTED BY ACTIVE TRANSPORT: Substances, which are transported actively, are in ionic form and non-ionic form.  ionic as sodium, potassium, calcium, hydrogen, chloride and iodide  non-ionic as glucose, amino acids and urea.
  15. 15. „CARRIER PROTEINS OF ACTIVE TRANSPORT 1. Uniport 2. Symport or antiport.
  16. 16. PROPERTIES OF ACTIVE TRANSPORT  Active  Needs carrier  Against concentration gradient
  17. 17. TYPES ACTIVE TRANSPORT: It is further devided into: A- Primary active transport B- Secondary active transport
  18. 18. Primary active transport  The energy is derived directly from the breakdown of ATP.
  19. 19. SECONDARY ACTIVE TRANSPORT  In the secondary active transport, the energy is derived secondarily from energy that has been stored in the form of ionic concentration differences between the two sides of a membrane.  Secondary active transport is the transport of a substance with sodium ion, by means of a common carrier protein. When sodium is transported by a carrier protein, another substance is also transported by the same protein simultaneously, either in the same direction (of sodium movement) or in the opposite direction. Thus, the transport of sodium is coupled with transport of another substance. Types of secondary active transport : 1- Cotransport, 2-Countertransport
  20. 20. ACTIVE TRANSPORT VS FACILITATED DIFFUSION Active transport mechanism is different from facilitated diffusion by two ways: 1.Carrier protein of active transport needs energy, whereas the carrier protein of facilitated diffusion does not need energy 2.In active transport, the substances are transported against the concentration or electrical or electrochemical gradient. In facilitated diffusion, the substances are transported along the concentration or electrical or electrochemical gradient.
  21. 21. SPECIAL TYPES OF PASSIVE TRANSPORT BULK FLOW: Bulk flow is the movement of large quantity of substances from a region of high pressure to the region of low pressure. It is due to the pressure gradient of the substances across the cell membrane
  22. 22. Bulk flow
  23. 23. FILTRATION: Movement of water and solutes from an area of high hydrostatic pressure to an area of low hydrostatic .
  24. 24. SPECIAL TYPES OF ACTIVE TRANSPORT 1. Endocytosis 2. Exocytosis 3. Transcytosis.
  25. 25. Endocytosis  Endocytosis is defined as a transport mechanism by which the macromolecules enter the cell. types: 1.Pinocytosis 2.Phagocytosis 3.Receptor-mediated endocytosis
  26. 26. PINOCYTOSIS: Pinocytosis is a process by which macromolecules like bacteria and antigens are taken into the cells. It is otherwise called the cell drinking.
  27. 27. Phagocytosis:  Phagocytosis is the process by which particles larger than the macromolecules are engulfed into the cells.  It is also called cell eating.  Larger bacteria, larger antigens and other larger foreign bodies are taken inside the cell by means of phagocytosis.  Only few cells in the body like neutrophils, monocytes and the tissue macrophages show phagocytosis.  Among these cells, the macrophages are the largest phagocytic cells.
  28. 28. MECHANISM OF PHAGOCYTOSIS i.When bacteria or foreign body enters the body, first the phagocytic cell sends cytoplasmic extension (pseudopodium) around bacteria or foreign body. ii.Then, these particles are engulfed and are converted into endosome like vacuole. Vacuole is very large and it is usually called the phagosome. iii. Phagosome travels into the interior of cell. iv.Primary lysosome fuses with this phagosome and forms secondary lysosome. v.Hydrolytic enzymes present in the secondary lysosome are activated resulting in digestion and degradation of the phagosomal contents.
  29. 29. RECEPTOR-MEDIATED ENDOCYTOSIS  The transport of macromolecules with the help of a receptor protein.  Surface of cell membrane has some pits (receptor-coated pit) which contain a receptor protein called clathrin.  These receptor-coated pits are involved in the receptor- mediated endocytosis.
  30. 30. Mechanism of receptor-mediated endocytosis:  Receptor-mediated endocytosis is induced by substances like ligands  Ligand molecules approach the cell and bind to receptors in the coated pits and form ligand- receptor complex.  Ligand-receptor complex gets aggregated in the coated pits. Then, the pit is detached from cell membrane and becomes the coated vesicle. This coated vesicle forms the endosome.
  31. 31.  Primary lysosome in the cytoplasm fuses with endosome and forms secondary lysosome.  Now, the hydrolytic enzymes present in secondary lysosome are activated resulting in release of ligands into the cytoplasm.  Clathrin is recycled into a new pit of the cell Membrane.
  32. 32. TRANSCYTOSIS:  Transporting the substances between two environments across the cells without any distinct change in the composition of these environments.  Trans-cytosis is a transport mechanism in which an extracellular macromolecule  Enters through one side of a cell,  migrates across cytoplasm of the cell  and exits through the other side.
  33. 33. MECHANISM OF TRANSCYTOSIS  Transcytosis involves the receptor-coated pits as in receptor-mediated endocytosis.  Receptor protein coating the pits is caveolin and not clathrin.  Transcytosis is also called, vesicle trafficking.  Examples  the movement of proteins from capillary blood into interstitial fluid across the endothelial cells of the capillary.  pathogens like human immuno deficiency virus (HIV)