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Cell membrane

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Mohammad A. Nassir

- Cells are composed of a nucleus surrounded by a nuclear membrane and cytoplasm surrounded by a plasma membrane. The plasma membrane is made mainly of proteins and lipids arranged in a bilayer that allows some substances to pass through, while preventing others. - There are two main types of transport across the plasma membrane: passive transport such as simple diffusion of lipid-soluble substances and facilitated diffusion through membrane proteins; and active transport using membrane proteins that require energy to move substances against a concentration gradient. - Osmosis is the diffusion of water across a semipermeable membrane according to the concentration of solutes on each side. It allows water to move from an area of high water concentration and low solutes to an area

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Objectives: -Cell structure. -Cell membrane. -Transport mechanism through cell membrane.
ORGANIZATION OF THE CELL cells consist of a nucleus surrounded by a nuclear membrane, and a cytoplasm surrounded by plasma membrane. cellular components (protoplasm) are made of : 1- water 2- Ions 3- proteins 4- lipids 5- carbohydrates
Cell membrane Thin, pliable and almost entirely made of proteins and lipids the lipid bilayer impedes water penetration cell membrane proteins are of two types: integral and peripheral, these proteins perform various functions (channels, carriers, receptors, enzymes, controllers)
TRANSPORT THROUGH CELL MEMBRANE The lipid bilayer prevents mixing of ECF & ICF water and water-soluble substances cannot move freely through it. lipid-soluble substances move freely through the plasma membrane Water, ions and water-soluble substances are transported through proteins (channel proteins & carriers)
Transport pathways through cell membrane
Constant motion of molecules, ions, colloid particles through cell membrane Two types: 1-Simple diffusion. 2-facilitated. diffusion
Diffusion
Simple diffusion Diffusion of a matter through the lipid bilayer is determined by its lipid solubility (O2, N2 ,CO2 move easily through the membrane) Water and some water-soluble substances (urea) pass through channels pores in proteins that penetrate all the way through the membrane Diffusion through channels is characterized by: 1-selective permeability (charge) , (size) 2-controled by opening and closing gates (voltage, ligand)
Carrier-mediated diffusion the rate of diffusion reaches a maximum (Vmax) According to Ficks law, the rate of diffusion depends on: 1-the magnitude of the concentration gradient 2-the permeability of the plasma membrane to a substance. 3-the surface area of the membrane across which diffusion takes place 4-the molecular weight of a substance 5-the distance through which diffusion takes place Facilitated diffusion
Cell membrane
Cell membrane
Fig. 3-14a, p. 56 Step 1 Conformation X of carrier (binding sites exposed to ECF) Molecule to be transported binds to carrier Molecule to be transported Concentration gradient Plasma membrane Carrier molecule (Low) (High)ECF ICF
Fig. 3-14b, p. 56 Step 2 On binding with molecules to be transported, carrier changes its conformation Conformation X of carrier ConformationY of carrier
Fig. 3-14c, p. 56 Step 3 ConformationY of carrier (binding sites exposed to ICF) Transported molecule detaches from carrier Direction of transport ECF ICF
Fig. 3-14d, p. 56 Step 4 ECF ICF Conformation X of carrier (binding sites exposed to ECF) After detachment, carrier reverts to original shape
II. ActiveTransport: Primary : - Secondary Na-K pump Co- & counter-tr. Ca - pump Na - Gl Na -aa H - pump Na -H Na - Ca
Cell membrane
Fig. 3-16, p. 58 Phosphorylated conformationY of carrier Step 1 Phosphorylated conformationY of carrier has high affinity for passenger. Molecule to be transported binds to carrier on low-concentration side. Molecule to be transported Step 2 Dephosphorylated conformation X of carrier has low affinity for passenger. Transported molecule detaches from carrier on high-concentration side. = phosphate Direction of transport Concentration gradient (High) (Low) Dephosphorylated conformation X of carrier ICF ECF Na+
Fig. 3-17, p = Sodium (Na+) = Potassium (K+) = Phosphate When open to the ECF, the carrier drops off Na+ on its high-concentration side and picks up K+ from its low-concentration side Phosphorylated conformationY of Na+K+ pump has high affinity for Na+ and low affinity for K+ when exposed to ICF When open to the ICF, the carrier picks up Na+ from its low-concentration side and drops off K+ on its high-concentration side Dephosphorylated conformation X of Na+K+ pump has high affinity for K+ and low affinity for Na+ when exposed to ECF ICF ECF
Cell membrane
Cell membrane
Transport of big particles - Endocytosis - Exocytosis - Pancytosis
Basic principles of osmosis: water diffuses from high [H2O] to region of lower [H2O] . (Kinetics). Osmosis
Cell membrane
OSMOTIC PRESSURE the exact amount of pressure required to stop osmosis. osmotic pressure is determined by the number of particles rather than their mass. osmole: 1 gram molecular weight of osmotically active solute a solution having 1 osmole of solute dissolved in each Kg of water is said to have an osmolality of 1 osmole/Kg 1 milliosmole/liter 19.3 mmHg osmotic pressure at normal body temperature
Osmosis across selectively permeable membranes
Fig. 3-9, p. 53 100% water concentration 0% solute concentration 90% water concentration 10% solute concentration = Water molecule = Solute molecule
Fig. 3-10, p. 53 Membrane Higher H2O concentration, lower solute concentration Lower H2O concentration, higher solute concentration = Water molecule = Solute molecule H2O
Fig. 3-11, p. 53 Membrane (permeable to both water and solute) Side 1 Side 2 Higher H2O concentration, lower solute concentration Lower H2O concentration, higher solute concentration H2O moves from side 1 to side 2 down its concentration gradient Solute moves from side 2 to side 1 down its concentration gradient Water concentrations equal Solute concentrations equal No further net diffusion Steady state exists Side 1 Side 2 = Water molecule = Solute molecule H2O Solute
Fig. 3-12, p. 54 = Water molecule = Solute molecule Membrane (permeable to H2O but impermeable to solute) Higher H2O concentration, lower solute concentration Lower H2O concentration, higher solute concentration H2O moves from side 1 to side 2 down its concentration gradient Water concentrations equal Solute concentrations equal No further net diffusion Steady state exists Solute unable to move from side 2 to side 1 down its concentration gradient Side 1 Side 2 Side 1 Side 2 Original level of solutions H2O
Fig. 3-13, p. 54 = Water molecule = Solute molecule Membrane (permeable to H2O but impermeable to solute) Pure water Lower H2O concentration, higher solute concentration H2O moves from side 1 to side 2 down its concentration gradient Solute unable to move from side 2 to side 1 down its concentration gradient Side 1 Side 2 Side 1 Side 2 Original level of solutions H2O Water concentrations not equal Solute concentrations not equal Tendency for water to diffuse by osmosis into side 2 is exactly balanced by opposing tendency for hydrostatic pressure difference to push water into side 1 Osmosis ceases Opposing pressure necessary to completely stop osmosis is equal to osmotic pressure of solution Hydrostatic (fluid) pressure difference Osmosis Hydrostatic pressure
1 osmole = 1 mole of solute particles (6.02 x10). 1 mole glucose = 1 osm. 1 mole NaCl = 2 osm. 1 mole Na2SO3 = 3 osm. Relation between moles and osmoles
- Osmolality and osmolarity in human fluids are equal.
Osmotic pressure : pressure that prevents the osmosis . The higher the osmotic pressure of a solution, the lower its [H2O] but the higher its [solute]. According to vant hoffs law: = CRT = 19300 mm Hg for 1 osmole/liter at body temp. (osmotic pr.) C(solute con. In osmole/liter) R (ideal gas const.) T(absolute temp.)
osmotic pr. = osmolarity(mOsm/L) X 19.3 mmHg the calculated value is not 100% correct due to intraionic and intermolecular interactions between the particles and it has to be multiplied by the osmotic coefficient of the particles to reach the true value. the osmolarity of the body fluids is around 300 mOsm/L, the plasma being 1mOsm/L higher because of the osmotic effect of plasma proteins

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Cell membrane

  • 2. ORGANIZATION OF THE CELL cells consist of a nucleus surrounded by a nuclear membrane, and a cytoplasm surrounded by plasma membrane. cellular components (protoplasm) are made of : 1- water 2- Ions 3- proteins 4- lipids 5- carbohydrates
  • 3. Cell membrane Thin, pliable and almost entirely made of proteins and lipids the lipid bilayer impedes water penetration cell membrane proteins are of two types: integral and peripheral, these proteins perform various functions (channels, carriers, receptors, enzymes, controllers)
  • 4. TRANSPORT THROUGH CELL MEMBRANE The lipid bilayer prevents mixing of ECF & ICF water and water-soluble substances cannot move freely through it. lipid-soluble substances move freely through the plasma membrane Water, ions and water-soluble substances are transported through proteins (channel proteins & carriers)
  • 6. Constant motion of molecules, ions, colloid particles through cell membrane Two types: 1-Simple diffusion. 2-facilitated. diffusion
  • 8. Simple diffusion Diffusion of a matter through the lipid bilayer is determined by its lipid solubility (O2, N2 ,CO2 move easily through the membrane) Water and some water-soluble substances (urea) pass through channels pores in proteins that penetrate all the way through the membrane Diffusion through channels is characterized by: 1-selective permeability (charge) , (size) 2-controled by opening and closing gates (voltage, ligand)
  • 9. Carrier-mediated diffusion the rate of diffusion reaches a maximum (Vmax) According to Ficks law, the rate of diffusion depends on: 1-the magnitude of the concentration gradient 2-the permeability of the plasma membrane to a substance. 3-the surface area of the membrane across which diffusion takes place 4-the molecular weight of a substance 5-the distance through which diffusion takes place Facilitated diffusion
  • 12. Fig. 3-14a, p. 56 Step 1 Conformation X of carrier (binding sites exposed to ECF) Molecule to be transported binds to carrier Molecule to be transported Concentration gradient Plasma membrane Carrier molecule (Low) (High)ECF ICF
  • 13. Fig. 3-14b, p. 56 Step 2 On binding with molecules to be transported, carrier changes its conformation Conformation X of carrier ConformationY of carrier
  • 14. Fig. 3-14c, p. 56 Step 3 ConformationY of carrier (binding sites exposed to ICF) Transported molecule detaches from carrier Direction of transport ECF ICF
  • 15. Fig. 3-14d, p. 56 Step 4 ECF ICF Conformation X of carrier (binding sites exposed to ECF) After detachment, carrier reverts to original shape
  • 16. II. ActiveTransport: Primary : - Secondary Na-K pump Co- & counter-tr. Ca - pump Na - Gl Na -aa H - pump Na -H Na - Ca
  • 18. Fig. 3-16, p. 58 Phosphorylated conformationY of carrier Step 1 Phosphorylated conformationY of carrier has high affinity for passenger. Molecule to be transported binds to carrier on low-concentration side. Molecule to be transported Step 2 Dephosphorylated conformation X of carrier has low affinity for passenger. Transported molecule detaches from carrier on high-concentration side. = phosphate Direction of transport Concentration gradient (High) (Low) Dephosphorylated conformation X of carrier ICF ECF Na+
  • 19. Fig. 3-17, p = Sodium (Na+) = Potassium (K+) = Phosphate When open to the ECF, the carrier drops off Na+ on its high-concentration side and picks up K+ from its low-concentration side Phosphorylated conformationY of Na+K+ pump has high affinity for Na+ and low affinity for K+ when exposed to ICF When open to the ICF, the carrier picks up Na+ from its low-concentration side and drops off K+ on its high-concentration side Dephosphorylated conformation X of Na+K+ pump has high affinity for K+ and low affinity for Na+ when exposed to ECF ICF ECF
  • 22. Transport of big particles - Endocytosis - Exocytosis - Pancytosis
  • 23. Basic principles of osmosis: water diffuses from high [H2O] to region of lower [H2O] . (Kinetics). Osmosis
  • 25. OSMOTIC PRESSURE the exact amount of pressure required to stop osmosis. osmotic pressure is determined by the number of particles rather than their mass. osmole: 1 gram molecular weight of osmotically active solute a solution having 1 osmole of solute dissolved in each Kg of water is said to have an osmolality of 1 osmole/Kg 1 milliosmole/liter 19.3 mmHg osmotic pressure at normal body temperature
  • 27. Fig. 3-9, p. 53 100% water concentration 0% solute concentration 90% water concentration 10% solute concentration = Water molecule = Solute molecule
  • 28. Fig. 3-10, p. 53 Membrane Higher H2O concentration, lower solute concentration Lower H2O concentration, higher solute concentration = Water molecule = Solute molecule H2O
  • 29. Fig. 3-11, p. 53 Membrane (permeable to both water and solute) Side 1 Side 2 Higher H2O concentration, lower solute concentration Lower H2O concentration, higher solute concentration H2O moves from side 1 to side 2 down its concentration gradient Solute moves from side 2 to side 1 down its concentration gradient Water concentrations equal Solute concentrations equal No further net diffusion Steady state exists Side 1 Side 2 = Water molecule = Solute molecule H2O Solute
  • 30. Fig. 3-12, p. 54 = Water molecule = Solute molecule Membrane (permeable to H2O but impermeable to solute) Higher H2O concentration, lower solute concentration Lower H2O concentration, higher solute concentration H2O moves from side 1 to side 2 down its concentration gradient Water concentrations equal Solute concentrations equal No further net diffusion Steady state exists Solute unable to move from side 2 to side 1 down its concentration gradient Side 1 Side 2 Side 1 Side 2 Original level of solutions H2O
  • 31. Fig. 3-13, p. 54 = Water molecule = Solute molecule Membrane (permeable to H2O but impermeable to solute) Pure water Lower H2O concentration, higher solute concentration H2O moves from side 1 to side 2 down its concentration gradient Solute unable to move from side 2 to side 1 down its concentration gradient Side 1 Side 2 Side 1 Side 2 Original level of solutions H2O Water concentrations not equal Solute concentrations not equal Tendency for water to diffuse by osmosis into side 2 is exactly balanced by opposing tendency for hydrostatic pressure difference to push water into side 1 Osmosis ceases Opposing pressure necessary to completely stop osmosis is equal to osmotic pressure of solution Hydrostatic (fluid) pressure difference Osmosis Hydrostatic pressure
  • 32. 1 osmole = 1 mole of solute particles (6.02 x10). 1 mole glucose = 1 osm. 1 mole NaCl = 2 osm. 1 mole Na2SO3 = 3 osm. Relation between moles and osmoles
  • 33. - Osmolality and osmolarity in human fluids are equal.
  • 34. Osmotic pressure : pressure that prevents the osmosis . The higher the osmotic pressure of a solution, the lower its [H2O] but the higher its [solute]. According to vant hoffs law: = CRT = 19300 mm Hg for 1 osmole/liter at body temp. (osmotic pr.) C(solute con. In osmole/liter) R (ideal gas const.) T(absolute temp.)
  • 35. osmotic pr. = osmolarity(mOsm/L) X 19.3 mmHg the calculated value is not 100% correct due to intraionic and intermolecular interactions between the particles and it has to be multiplied by the osmotic coefficient of the particles to reach the true value. the osmolarity of the body fluids is around 300 mOsm/L, the plasma being 1mOsm/L higher because of the osmotic effect of plasma proteins
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