Molecular Cell Biology[MCB-Rupendra Shrestha]

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Molecular Cell Biology:

Molecular Cell Biology Principles of Membrane Transport Sri Ramachandra Medical College and Research Institute Porur, Chennai – 600 116 Mr. Rupendra Shrestha; PG Human Genetics Acknowledge to Mrs. R. Selvi

Outline:

Outline Knowledged by Mr.Rupendra Shrestha

PowerPoint Presentation:

Knowledged by Mr.Rupendra Shrestha

Cell Membrane:

Cell Membrane Knowledged by Mr.Rupendra Shrestha

The Cell Membrane Fluid Mosaic Model:

Knowledged by Mr.Rupendra Shrestha The Cell Membrane Fluid Mosaic Model Fluid mosaic model of cell membrane A fluid mosaic describes the organization of cell membranes as flexible, not solid and fixed Phospholipids drift and move like a fluid The bilayer is a mosaic mixture of phospholipids, steroids, proteins, and other molecules So, the cell membrane is not solid/static/fixed but rather elastic and adaptable to changing needs

The Cell Fluid Mosaic Model:

Knowledged by Mr.Rupendra Shrestha The Cell Fluid Mosaic Model

Variations On The Fluid Mosaic Model:

Knowledged by Mr.Rupendra Shrestha Variations On The Fluid Mosaic Model Differences in membrane composition Different kinds and numbers of carbohydrates are attached to membrane proteins Different kinds of phospholipids may be present Differences in fluidity Some proteins are attached to the cytoskeleton; others just drift around Archaeans have more rigid membranes than either bacteria or eukaryotes

Cell Membrane Composition:

Cell Membrane Composition Plasma membrane encloses cell and cell organelles Made of hydrophobic and hydrophilic components Semi-permeable and fluid-like “lipid bilayer” Knowledged by Mr.Rupendra Shrestha

Cell Membrane Composition:

Integral proteins interact with “lipid bilayer” Passive transport pores and channels Active transport pumps and carriers Membrane-linked enzymes, receptors and transducers Sterols stabilize the lipid bilayer Cholesterol Cell Membrane Composition Knowledged by Mr.Rupendra Shrestha

PowerPoint Presentation:

Knowledged by Mr.Rupendra Shrestha

PowerPoint Presentation:

Knowledged by Mr.Rupendra Shrestha

Solution – mixture of dissolved molecules in a liquid Solute – the substance that is dissolved Solvent – the liquid :

Solution – mixture of dissolved molecules in a liquid Solute – the substance that is dissolved Solvent – the liquid Membrane Transport Knowledged by Mr.Rupendra Shrestha

Movement of Small Molecules:

Movement of Small Molecules Knowledged by Mr.Rupendra Shrestha

Ion Concentrations:

Ion Concentrations The maintenance of solutes on both sides of the membrane is critical to the cell Helps to keep the cell from rupturing Concentration of ions on either side varies widely Na + and Cl - are higher outside the cell K + is higher inside the cell Must balance the the number of positive and negative charges, both inside and outside cell Knowledged by Mr.Rupendra Shrestha

Impermeable Membranes:

Impermeable Membranes Ions and hydrophilic molecules cannot easily pass thru the hydrophobic membrane Small and hydrophobic molecules can Must know the list to the left

Membrane Transport Proteins:

Membrane Transport Proteins Many molecules must move back and forth from inside and outside of the cell Most cannot pass through without the assistance of proteins in the membrane bilayer Private passageways for select substances Each cell has membrane has a specific set of proteins depending on the cell Knowledged by Mr.Rupendra Shrestha

PowerPoint Presentation:

Knowledged by Mr.Rupendra Shrestha

2 Major Classes:

2 Major Classes Carrier proteins – move the solute across the membrane by binding it on one side and transporting it to the other side Requires a conformation change Channel protein – small hydrophilic pores that allow for solutes to pass through Use diffusion to move across Also called ion channels when only ions moving Knowledged by Mr.Rupendra Shrestha

Proteins:

Proteins Knowledged by Mr.Rupendra Shrestha

Carrier vs Channel:

Carrier vs Channel Channels, if open, will let solutes pass if they have the right size and charge Trapdoor-like Carriers require that the solute fit in the binding site Turnstile-like Why carriers are specific like an enzyme and its substrate Knowledged by Mr.Rupendra Shrestha

PowerPoint Presentation:

Knowledged by Mr.Rupendra Shrestha

Mechanisms of Transport:

Mechanisms of Transport Provided that there is a pathway, molecules move from a higher to lower concentration Doesn’t require energy Passive transport or facilitated diffusion Movement against a concentration gradient requires energy (low to high) Active transport Requires the harnessing of some energy source by the carrier protein Special types of carriers Knowledged by Mr.Rupendra Shrestha

Modes of Transport:

Modes of Transport Knowledged by Mr.Rupendra Shrestha

Carrier Proteins:

Carrier Proteins Required for almost all small organic molecules Exception – fat-soluble molecules and small uncharged molecules that can pass by simple diffusion Usually only carry one type of molecule Carriers can also be in other membranes of the cell such as the mitochondria Knowledged by Mr.Rupendra Shrestha

Carriers in the Cell:

Carriers in the Cell Knowledged by Mr.Rupendra Shrestha

Carrier-Mediated Transport:

Carrier-Mediated Transport Integral protein binds to the solute and undergo a conformational change to transport the solute across the membrane Knowledged by Mr.Rupendra Shrestha

Channel Mediated Transport:

Channel Mediated Transport Proteins form aqueous pores allowing specific solutes to pass across the membrane Allow much faster transport than carrier proteins Knowledged by Mr.Rupendra Shrestha

Coupled Transport:

Coupled Transport Some solutes “go along for the ride” with a carrier protien or an ionophore Can also be a Channel coupled transport Knowledged by Mr.Rupendra Shrestha

Voltage Across the Membrane:

Voltage Across the Membrane Charged molecules have another component – a voltage across the membrane = membrane potential Cytoplasm is usually negative relative to the outside, pulls in positive charges and move out negative charges Movement across membrane is under 2 forces – electrochemical gradient Concentration gradient Voltage across the membrane Knowledged by Mr.Rupendra Shrestha

Electrochemical Gradient:

Electrochemical Gradient This gradient determines the direction of the solute during passive transport

PowerPoint Presentation:

Passive Transport Knowledged by Mr.Rupendra Shrestha

PowerPoint Presentation:

Knowledged by Mr.Rupendra Shrestha

Passive Transport:

Passive Transport Process that moves materials across the plasma membrane D oes not require energy from the cell Materials move with the concentration gradient: high concentration low concentration 3 Kinds: Diffusion, Osmosis, and Facilitated Diffusion S-B-7-3_Passive Transport PPT

Passive Transport by Glucose Carrier:

Passive Transport by Glucose Carrier Glucose carrier consists of a protein chain that crosses the membrane about 12 times and has at least 2 conformations – switch back and forth One conformation exposes the binding site to the outside of the cell and the other to the inside of the cell

How it Works ?:

How it Works ? Glucose is high outside the cell so the conformation is open to take in glucose and move it to the cytosol where the concentration is low When glucose levels are low in the blood, glucagon (hormone) triggers the breakdown of glycogen (e.g., from the liver), glucose levels are high in the cell and then the conformation moves the glucose out of the cell to the blood stream Glucose moves according to the concentration gradient across the membrane Can move only D-glucose, not mirror image L-glucose Knowledged by Mr.Rupendra Shrestha

Diffusion :

Diffusion Migration of atoms, ions, molecules or even small particles through random motion due to thermal energy A particle at any absolute temperature T has an average kinetic energy of 3kT/2, where k is Bolzmann’s Constant. The value of kT at 300 o K is 4.14X10 -14 g/cm 2 /sec 2 . Particle size is not a factor in this calculation. Therefore, the mean velocity of a diffusing particle depends on its mass, so that particles of different masses have different diffusion coefficients. Knowledged by Mr.Rupendra Shrestha

Diffusing particles undergo random walks:

Diffusing particles undergo random walks Because of collisions with other particles, a diffusing particle changes direction on a picosecond time scale. Therefore, individual particles move about randomly and tend to return to the same spots. However, if there is a concentration gradient, the average number of particles moving down the gradient at any instant will be greater than the number moving up the gradient: there will be a net flux (J net ) of particles from the higher concentration toward the lower concentration. Therefore, it helps to think of the concentration gradient as a force that drives particle movement, even though from the point of view of an individual particle, all movements are random. Knowledged by Mr.Rupendra Shrestha

What a random movement looks like:

What a random movement looks like N=18,050 steps – the particle has moved a distance made good of 196 step lengths Knowledged by Mr.Rupendra Shrestha

Permeation through membranes:

Permeation through membranes If a barrier to free diffusion is inserted into the system (such as a cell’s plasma membrane), a permeability coefficient replaces the term for the diffusion coefficient . Knowledged by Mr.Rupendra Shrestha

How does diffusion physics relate to physiology?:

How does diffusion physics relate to physiology? Delivery and removal of substances by diffusion sets an upper limit on cell diameter of about 100 microns. Since surface area is a term in the 3D Fick equation, structures that must maximize diffusional flux tend to show expanded surface area and attenuated linear dimensions. (Think of the anatomy of the lung or the surface of the intestine). Knowledged by Mr.Rupendra Shrestha

Osmosis:

Osmosis The movement of water from region of low solute concentration (high water concentration) to an area of high solute concentration (low water concentration) Driving force is the osmotic pressure caused by the difference in water pressure Knowledged by Mr.Rupendra Shrestha

Osmosis:

Osmosis Diffusion of water across a selectively permeable membrane. Does not require energy from the cell.

The rule for osmosis: If the area outside the cell has more salt, then water will be sucked out of the cell. :

The rule for osmosis: If the area outside the cell has more salt, then water will be sucked out of the cell. S-B-7-3_Passive Transport PPT

Osmotic Solutions – Tonicity (tonos = tension):

Osmotic Solutions – Tonicity ( tonos = tension) Isotonic – equal solute on each side of the membrane Hypotonic – less solute outside cell, water rushes into cell and cell bursts Hypertonic – more solute outside cell, water rushes out of cell and cell shrivels

Osmotic flow:

Osmotic flow In osmosis, water diffuses along a gradient of water concentration that is the result of dilution of water by the presence of solvents –i.e. the higher the solvent concentration, the lower the water concentration The potential energy for water movement represented by a solute concentration gradient is given by the van t’Hoff Equation. @ P osm = MRT Where, the units of P osm are atmospheres, M is the osmolality of the solution, R is the gas constant, and T is the absolute temperature. Generally, a correction has to be added to the van t’Hoff eq. to correct for non-ideal behavior of the solute. Knowledged by Mr.Rupendra Shrestha

Colligative properties of solutions:

Colligative properties of solutions Osmotic pressure Freezing point Vapor pressure or boiling point Note:-Colligative means “tied together”. The higher the solute concentration, the higher the osmotic pressure, the lower the freezing point and the higher the boiling point, compared to pure water. Knowledged by Mr.Rupendra Shrestha

Osmotic Properties of Cells:

Osmosis (Greek, osmos “to push”) Movement of water down its concentration gradient. Hydrostatic pressure Movement of water causes fluid mechanical pressure Pressure gradient across a semi-permeable membrane Osmotic Properties of Cells Knowledged by Mr.Rupendra Shrestha

Hydrostatic pressure:

Hydrostatic pressure Knowledged by Mr.Rupendra Shrestha

PowerPoint Presentation:

Knowledged by Mr.Rupendra Shrestha

Membrane Transport:

Membrane Transport The most important property of membranes is their ability to control the rate of permeation of different species. The 2 models used to describe the mechanism of permeation are the pore flow model and the solution-diffusion model. In the solution-diffusion model , the permeants dissolve in the membrane material and then diffuse through the membrane down a concentration gradient. The permeants are separated because of the differences in the solubilities of the materials in the membrane and the differences in the rates at which the materials diffuse through the membrane. This transport mechanism occurs in the reverse osmosis, pervaporation and polymeric gas separation membranes. Knowledged by Mr.Rupendra Shrestha

Contd…:

Contd… In the pore flow model , permeants are transported by pressure-driven convective flow through tiny pores. Separation occurs because one of the permeants is excluded (filtered) from some of the pores in the membrane through which other permeants move. This transport mechanism occurs in the ultrafiltration, microfiltration and  microporous gas flow membranes. Knowledged by Mr.Rupendra Shrestha

Osmotic Pressure in Biology :

Osmotic Pressure in Biology Cells contain solutes Some solutes can permeate the plasma membrane, others cannot. Since impermeable solutes (typically ions) remain within the cell, water will always move toward the inside of the cell due to osmosis. If this is so, how do we prevent lysis? But it’s even more complicated than that! Gibbs-Donnan forces are the essence of LIFE They establish that “Dynamic Disequilibrium” Knowledged by Mr.Rupendra Shrestha

Gibbs-Donnan “Equilibrium” Semipermeable Membrane:

Gibbs-Donnan “Equilibrium” Semipermeable Membrane What would happen if two water filled, 1L compartments were separated by a rigid membrane, and a permeable solute, say 12 millimoles of NaCl, were put into one compartment but not the other? Knowledged by Mr.Rupendra Shrestha 12 Nacl 12Na + 12Cl - Inside outside

Gibbs-Donnan “Equilibrium”:

Gibbs-Donnan “Equilibrium” Water would move toward the solute (osmosis) while solute would diffuse down its concentration gradient into the water. Since water would typically move faster , the fluid would overflow on the side with the solute. Knowledged by Mr.Rupendra Shrestha 12 Nacl 12Na + 12Cl - water Inside outside

Gibbs-Donnan “Equilibrium”:

Gibbs-Donnan “Equilibrium” But, if we were to fasten a lid on the chambers to prevent osmosis, what would happen then? Knowledged by Mr.Rupendra Shrestha 12 Nacl 12Na + 12Cl - Inside outside

Gibbs-Donnan “Equilibrium”:

Gibbs-Donnan “Equilibrium” Solute would redistribute following the second law, attempting to reach equilibrium. Since water could not move by osmosis the volume of each compartment would remain the same. Knowledged by Mr.Rupendra Shrestha 12 Na + 12 Cl - Inside Outside

Gibbs-Donnan “Equilibrium”:

Gibbs-Donnan “Equilibrium” Eventually the solutes would reach equilibrium, with equal amounts of each solute on each side of the membrane. Knowledged by Mr.Rupendra Shrestha 6Na + 6Na + 6Cl - 6Cl - Inside Outside The small ions will distribute throughout the system, based upon electrochemical gradient. Add 12 molecules of small monovalent salts and allow to equillibrium + _ 6(+), 6(-) 6(+),6(-) + + _ + + _ _ _ + _ + _ + _ +_ _ _ _ + + +

Gibbs-Donnan “Equilibrium”:

Gibbs-Donnan “Equilibrium” What if we then added some salt of an  impermeable ion? Eg .  3mmoles of K 4Pr which would dissociate to 12K + and 3Pr 4- Solute would redistribute, attempting to reach  equilibrium.  But the  impermeable ion would  prevent ionic equilibration Knowledged by Mr.Rupendra Shrestha 6Na+ 6Na+ 6Cl- 6Cl- 12K+ K+ 3Pr- Inside Outside

Gibbs-Donnan “Equilibrium”:

Gibbs-Donnan “Equilibrium” Recognize that as K+ moves down its concentration gradient it takes a + charge along with it and leaves a – charge behind, thus establishing an electrical disequilibrium which influences continued K+ movement. But, as + charge developed in the right side, Cl- will also begin to move across the membrane to equilibrate with the charge differential too. Knowledged by Mr.Rupendra Shrestha 6Na+ 6Na+ 6Cl- 6Cl- 12K K 3Pr- Inside Outside + +

Gibbs-Donnan Examples:

Gibbs-Donnan Examples Eventually the ion concentrations would stabilize (steady state) and individual solute concentrations would not change over time ; thus it would look like equilibrium. Here is an example Knowledged by Mr.Rupendra Shrestha 6Na+ - + 6Na+ 4Cl- - + 8Cl- 10K+ - + 2K+ 3Pr- - + Inside Outside

Gibbs-Donnan “Equilibrium”:

Gibbs-Donnan “Equilibrium” The small ions will distribute throughout the system,based upon electrochemical  gradient. The large impermeable ions will establish an electrochemical gradient leading to unequal distribution of the permeable ions. Knowledged by Mr.Rupendra Shrestha Add 12 molecules of small monovalent salts and allow to equillibrium + _ 6(+), 6(-) 6(+),6(-) + + _ + + _ _ _ + _ + _ + _ +_ _ _ _ + + + Add 3 molecule + +++ _ 8(+), 8(-) 16(+),4(-)+++ + + _ + + ++ +++ _ + ++_ _ _ + _ + _ + _ +_ _ + _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Allow for reequillibrium

Gibbs-Donnan Examples:

Gibbs-Donnan Examples Permeable ions will reach equilibrium across a membrane. Addition of salt of impermeable ion will result in redistribution of permeable ions to satisfy Gibbs- Donnan equilibrium conditions. Knowledged by Mr.Rupendra Shrestha 6Na + 6Na + 6Cl - 6Cl - Inside Outside 6Na+ 6Na+ 6Cl- 6Cl- 12K K 3Pr- Inside Outside + + 6Na+ - + 6Na+ 4Cl- - + 8Cl- 10K+ - + 2K+ 3Pr- - + Inside Outside

Gibbs-Donnan Phenomena:

Gibbs-Donnan Phenomena At “equilibrium” there will be a redistribution of permeable or diffusable ions, such that; 1.  (∑[ diffusable cations ] x ∑[ diffusable anions]) inside = (∑[diff. cations ] x ∑[diff. anions]) outside 2. Net electrical neutrality will be maintained. (inside = 0 and outside = 0) 3. The sum of diffusable (permeable) ions will be greater on the side with non- diffusable ions Knowledged by Mr.Rupendra Shrestha

Gibbs-Donnan Phenomena:

Gibbs-Donnan Phenomena At equilibrium there will be a redistribution of permeable or diffusable ions, such that; 1.  (∑[ diffusable cations ] x ∑[ diffusable anions])inside = (∑[diff. cations ] x ∑[diff. anions]) outside ([Na + + K + ]  x  [ Cl -])inside = ([Na+ + K+]  x  [ Cl -])outside (6  +  10)    x    4       =     (6  +  2)    x    8    =  64 Knowledged by Mr.Rupendra Shrestha

Gibbs-Donnan Phenomena:

Gibbs-Donnan Phenomena At equilibrium there will be a redistribution of permeable or diffusable ions, such that; 2. Net electrical neutrality will be maintained. (inside = 0 and outside = 0) 16 +   8 + - 16 – - 8 – 0   inside 0   outside Knowledged by Mr.Rupendra Shrestha

Gibbs-Donnan Phenomena:

Gibbs-Donnan Phenomena At equilibrium there will be a redistribution of permeable or diffusable ions, such that; 3. The sum of diffusable (permeable) ions will be greater on the side with non- diffusable ions. 6  +  10  +  4  =  20   (add non-diff. = 23) inside, vs. 6  +  2  +  8  =  16 outside Knowledged by Mr.Rupendra Shrestha

Gibbs-Donnan Examples:

Gibbs-Donnan Examples 1) ([Na+ + K+]  x  [ Cl -]) inside =  ([Na+ + K+]  x  [ Cl -]) outside (6  +  10)      x      4       =      (6  +  2)    x    8    =  64 2) 16 +   8 + 16 – 8 – 0   inside 0   outside 3) 6  +  10  +  4  =  20   (add non-diff. = 23) inside, vs. 6  +  2  +  8  =  16 outside Knowledged by Mr.Rupendra Shrestha

Gibbs-Donnan “Equilibrium”:

Gibbs-Donnan “Equilibrium” This will establish an electrical potential at the membrane to counteract these movements: positive charge outside (gain of K+) will repel K+ and attract Cl– negative charge inside will attract K+ and repel Cl– Knowledged by Mr.Rupendra Shrestha 6Na+ 6Na+ 6Cl- 6Cl- 12K+ 3Pr- Inside Outside 6Na+ - + 6Na+ 4Cl- - + 8Cl- 10K+ - + 2K+ 3Pr- - + Inside Outside

Gibbs-Donnan “Equilibrium”:

Gibbs-Donnan “Equilibrium” Note that the average charge within each compartment, as measured with the pipettes, remains approximately 0; only at the surface of the membrane is there a separation of charge Knowledged by Mr.Rupendra Shrestha +-+-+-+-+-+- +-+-+-+-+-+-+- -+-+-+-+-+-+ -+-+-+-+-+-+-+ +-+-+-+-+-+- +-+-+-+-+-+-+- -+-+-+-+-+-+ -+-+-+-+-+-+-+ +-+-+-+-+-+- +-+-+-+-+-+-+- -+-+-+-+-+-+ -+-+-+-+-+-+-+ +-+-+-+-+-+- +-+-+-+-+-+-+- -+-+-+-+-+-+ -+-+-+-+-+-+-+ +-+-+-+-+-+- +-+-+-+-+-+-+- -+-+-+-+-+-+ -+-+-+-+-+-+-+ +-+-+-+-+-+- +-+-+-+-+- -+-+-+-+-+-+ -+-+-+-+-+ +-+-+-+-+-+- +-+-+-+-+- -+-+-+-+-+-+ -+-+-+-+-+ +-+-+-+-+-+- +-+-+-+-+- -+-+-+-+-+-+ -+-+-+-+-+ +-+-+-+-+-+- +-+-+-+-+- -+-+-+-+-+-+ m -+-+-+-+-+ +-+-+-+-+-+- +-+-+-+-+- -+-+-+-+-+-+ -+-+-+-+-+ - - - - - - - - - - - - + + + + + + + + + + True Equilibrium Donnan Equilibrium

Gibbs- Donnan Phenomenon:

Gibbs- Donnan Phenomenon 1.  This implies need for evolution of pump to maintain osmotic equilibrium between cells and  Interstitial Fluid (ISF), across the cell membrane. 2.  G-D forces are responsible for development of a membrane charge due to passive processes. 3.  G-D forces are contributory to fluid and electrolyte distribution within various body compartments. 4.  For example, they contribute to maintenance of fluid distribution between the plasma and interstitial fluid.  Blood pressure pushes fluid out, into the ISF, but Gibbs- Donnan forces, due to plasma proteins and associated permeable ions hold fluid in, via osmosis. Knowledged by Mr.Rupendra Shrestha

Donnan Equilibrium:

Donnan Equilibrium Semi-permeable membrane Deionized water Add Ions Balanced charges among both sides Knowledged by Mr.Rupendra Shrestha

Donnan Equilibrium:

Add anion More Cl - leaves I to balance charges Donnan Equilibrium Diffusion Knowledged by Mr.Rupendra Shrestha

Ionic Steady State:

Ionic Steady State Potaasium cations most abundant inside the cell Chloride anions ions most abundant outside the cell Sodium cations most abundant outside the cell Knowledged by Mr.Rupendra Shrestha

Donnan equilibrium:

Donnan equilibrium [K + ] i K+ A- Na+ Ca2+ Na+ Na+ K+ K+ Cl- A- A- A- [K + ] ii [Cl - ] ii [Cl - ] i = Knowledged by Mr.Rupendra Shrestha

Erythrocyte cell equilibrium:

Erythrocyte cell equilibrium No osmotic pressure - cell is in an isotonic solution - Water does not cross membrane Increased [Osmotic] in cytoplasm - cell is in an hypotonic solution - Water enters cell, swelling Decreased [Osmotic] in cytoplasm - cell is in an hypertonic solution - Water leaves cell, shrinking Knowledged by Mr.Rupendra Shrestha

Cell Lysis:

Cell Lysis Using hypotonic solution Or interfering with Na+ equilibrium causes cells to burst This can be used to researchers’ advantage when isolating cells Knowledged by Mr.Rupendra Shrestha

Animal cells could never attain Gibbs-Donnan Equilibrium:

Animal cells could never attain Gibbs-Donnan Equilibrium Why not? The plasma membrane cannot sustain a hydrostatic pressure gradient. Without the evolution of some means of avoiding Gibbs- Donnan equilibrium, there would be no protein-containing cells. Knowledged by Mr.Rupendra Shrestha

The Na+/K+ Pump counteracts G-D Equilibration:

The Na + /K + Pump counteracts G-D Equilibration The Na + /K + pump undergoes cycles in which it spends an ATP to eject 3 Na + from the cell and at the same time to take 2 K + into the cell. On the average, this counteracts leakage of Na + and K + across the membrane down their electrochemical gradients. The bottom-line effect of this is to make the cell effectively impermeable to NaCl. Gibbs-Donnan equilibrium is not approached and the cell does not swell, in spite of the presence of protein anion (X - ). Knowledged by Mr.Rupendra Shrestha

What if the Na+/K+ pump stops working?:

What if the Na + /K + pump stops working? Knowledged by Mr.Rupendra Shrestha

Fick’s Law of Diffusion:

Fick’s Law of Diffusion Knowledged by Mr.Rupendra Shrestha Rate of diffusion surface area • concentration gradient • membrane permeability membrane thickness Extracellular fluid Membrane surface area Intracellular fluid Composition of lipid layer Lipid solubility Molecular size Concentration outside cell Concentration inside cell Membrane thickness Concentration gradient Fick's Law of Diffusion says : lipid solubility molecular size Membrane permeability Membrane permeability Changing the composition of the lipid layer can increase or decrease membrane permeability.

Fick’s Law of Diffusion:

Fick’s Law of Diffusion According to this law, amount of a substance crossing a given area is directly proportional to the area available for diffusion , concentration gradient and a constant known as diffusion coefficient . Diffusion Coefficient :- a constant, which is the measure of a substance diffusing through the concentration gradient . It is also known as diffusion constant . It is related to size and shape of molecules of the substance. Knowledged by Mr.Rupendra Shrestha

Fick’s Law of Diffusion:

Fick’s Law of Diffusion Thus, Amount diffused = area x concentration gradient x diffusion coefficient. Formula of Fick Law : J = -D x A x dc dx where, J = Amount of substance diffused D = Diffusion coefficient A = Area through which diffusion occurs dc/dx = Concentration Gradient Negative sign in the formula indicates that diffusion occurs from region of higher concentration to region of lower concentration. Diffusion coefficient reduces when the molecular size of diffusing substance is increased.it increased when the size is decreased , i.e. the smaller molecules diffuse rapidly than the larger ones. Knowledged by Mr.Rupendra Shrestha

Application Based on Fick’s Law:

Application Based on Fick’s Law Measurement of cardiac output by using Fick Principle Adolph Fick described Fick principle in 1870. According to this principle, the amount of a substance taken up by organ or by the whole body or given out in a unit time is the product of amount of blood flowing through the organ and the arteriovenous difference of the substance across the organ. Amount of substance given or taken = amount of blood flow/ minute x arteriovenous difference . Knowledged by Mr.Rupendra Shrestha

Application Based on Fick’s Law:

Application Based on Fick’s Law For example Amount of blood flowing through lungs = 5,000ml/minute O 2 content in arterial blood = 20ml/100ml of blood O 2 content in venous blood = 15ml/100ml of blood Amount of O 2 Moved = Amount of blood x Arteriovenous from lungs to blood flow/minute difference = 5,000 x 20 – 15 100 = 250ml/minute amount of O 2 flow from lungs to blood is 250 ml/minutes Knowledged by Mr.Rupendra Shrestha

Nernst law:

Nernst law An equation that can be used to determine the equilibrium reduction potential of a half-cell in an electrochemical cell. Can also be used to determine the total voltage for a full electrochemical cell. Named after German physical chemist Walther Nernst. Knowledged by Mr.Rupendra Shrestha

Nernst Law:

Nernst Law Ered = Ered-RT/Zf ln a Red/ a Ox (half cell reduction potential) Ecell = Ecell-RT/Zf ln Q(Total cell potential ) E = Eo-0.05916/Z log 10 a Red/ a Ox The above equation is the Nernst equation which is used in physiology for finding electric potential of cell membrane with respect to one type of ion. Knowledged by Mr.Rupendra Shrestha

Nernst Electrotonic Potential:

Nernst Electrotonic Potential If  ion ( eg . Na+ K+) was permeable to the membrane, the charge developed could be determined using the Nernst equation: R = gas constant   z = valence T = temp. (C)    F = Faraday constant Knowledged by Mr.Rupendra Shrestha

Nernst Electrotonic Potential:

Nernst Electrotonic Potential In the above example, the K+ concentrations used were approximately equal to the K+ concentrations found in the human body. Since the ratio [k+]o/[k+]i is less than 1,the log of a fraction is a negative number, we often write [k+]i/[k+]o an we insert -1 as a constant at beginning. Knowledged by Mr.Rupendra Shrestha E.P= 61 log [k+]o = 61log 5 =-90mV [K+]i 150 If only K+ were permeable to the membrane, then the membrane potential would be -90 mV

Biological Concentrations :

Biological Concentrations These are the physiological concentrations of some important electrolytes Knowledged by Mr.Rupendra Shrestha Note that the concentration ratio (outside/inside) for sodium is approximately opposite that for potassium.

Nernst Electrotonic Potential:

Nernst Electrotonic Potential Knowledged by Mr.Rupendra Shrestha E.P= 61 log [Na+] o = 61log 150mM =+61mV [Na+] i 15mM If only Na+ were permeable to the membrane, then the membrane potential would be +61 mV Physiological resting membrane potential-70mV

Nernst Potential:

Nernst Potential Previous studies have shown that, at rest, K+ is the most permeable cation, and is far more permeable than Na+. The membrane potential for many human cells at rest is between -60 and -90mV; further suggesting that the resting membrane potential is primarily due to K+ distribution via Gibbs-Donnan forces. Knowledged by Mr.Rupendra Shrestha

PowerPoint Presentation:

Knowledged by Mr.Rupendra Shrestha

Cell Permeability:

Cell Permeability Passive transport is carrier mediated Facilitated diffusion Solute molecule combines with a “carrier” or transporter Electrochemical gradients determines the direction Integral membrane proteins form channels Knowledged by Mr.Rupendra Shrestha

Molecules Related to Cell Permeability:

Molecules Related to Cell Permeability Depends on Molecules size (electrolytes more permeable) Polarity (hydrophillic) Charge (anion vs. cation) Water vs. lipid solubility Knowledged by Mr.Rupendra Shrestha

Crossing the membrane:

Crossing the membrane Simple or passive diffusion Passive transport Channels or pores Facilitated transport Assisted by membrane-floating proteins Active transport pumps & carriers ATP is required Enzymes and reactions may be required Knowledged by Mr.Rupendra Shrestha

Facilitated Diffusion (3rd form of passive transport):

Facilitated Diffusion (3 rd form of passive transport) Ions, sugars, amino acids need to permeate cell membranes Knowledged by Mr.Rupendra Shrestha

Facilitated Diffusion:

Facilitated Diffusion Uses no energy Moves from area of high concentration to low concentration (with concentration gradient) Uses transport proteins very selective- allows only 1 kind of particle through. Types: Channel and Carrier Knowledged by Mr.Rupendra Shrestha

Facilitated Diffusion:

Facilitated Diffusion channel carrier Knowledged by Mr.Rupendra Shrestha

Facilitated Diffusion:

Facilitated Diffusion Channel protein Forms simple pores Form water filled tunnels Various diameters & charges Size & charge of ions determine which pore they will pass thru(via). Knowledged by Mr.Rupendra Shrestha

Facilitated Diffusion:

Facilitated Diffusion Carrier proteins- more complex 2 modes of action: Particle fits into one side of protein, changes shape & releases particle on other side. Gates- 1 molecule bonds to carrier protein, gate opens, molecule passes thru http://wps.prenhall.com/wps/media/objects/486/498392/CDA4_2/CDA4_2a/CDA4_2a.htm Knowledged by Mr.Rupendra Shrestha

Facilitated Diffusion:

Facilitated Diffusion Carrier protein Knowledged by Mr.Rupendra Shrestha

Active transport:

Active transport uses energy (ATP). Cells in gills of saltwater fish pump out salt. Moves from area of low to high concentration, (against the concentration gradient). Allows stockpiling in cells- roots cells of plants take in lots of ions. Uses carrier proteins/pumps. Knowledged by Mr.Rupendra Shrestha

Active transport:

Active transport Molecules move against concentration gradient Knowledged by Mr.Rupendra Shrestha

Na+-K+ ATPase (Na+-K+ Pump):

Na + -K + ATPase (Na + -K + Pump) Requires ATP hydrolysis to maintain the Na + -K + equilibrium in the cell Transporter is also a ATPase (enzyme) This pump keeps the [Na + ] 10 to 30 times lower than extracellular levels and the [K + ] 10 to 30 times higher than extracellular levels Knowledged by Mr.Rupendra Shrestha

Na+-K+ Pump:

Na + -K + Pump Moves K + while moving Na + Works constantly to maintain [Na + ] inside the cell – Na + comes in thru other channels or carriers

Na+ and K+ Concentrations:

Na + and K + Concentrations The [Na + ] outside the cell stores a large amount of energy, like water behind a dam Even if the Na + -K + pump is halted, there is enough stored energy to conduct other Na + downhill reactions The [K + ] inside the cell does not have the same potential energy Electric force pulling K + into the cell is almost the same as that pushing it out of the cell Knowledged by Mr.Rupendra Shrestha

Na+/K+ Pump:

Against their electrochemical gradients For every 3 ATP, 3 Na+ out, 2 K+ in Na + /K + Pump Actively transport Na+ out of the cell and K+ into the cell Knowledged by Mr.Rupendra Shrestha

Na+/K+ Pump:

Na+ exchange (symport) is also used in epithelial cells in the gut to drive the absorption of glucose from the lumen, and eventually into the bloodstream (by passive transport) Na+/K+ Pump Knowledged by Mr.Rupendra Shrestha

PowerPoint Presentation:

Knowledged by Mr.Rupendra Shrestha

Na+/K+ Pump:

About 1/3 of ATP in an animal cell is used to power sodium-potassium pumps Na+/K+ Pump In electrically active nerve cells, which use Na+ and K+ gradients to propagate electrical signals, up to 2/3 of the ATP is used to power these pumps Knowledged by Mr.Rupendra Shrestha

Na+-K+ Pump is a Cycle:

Na + -K + Pump is a Cycle Knowledged by Mr.Rupendra Shrestha

Na+-K+ Mechanisms:

Na + -K + Mechanisms Pump adds a PO 4 + group so that it can pick up 3 Na + When 3 Na + are in place, change shape and pump Na + out Opens site for 2 K + to bind, when in place, PO 4 + group is removed and it changes to original shape Dumps K + to inside, reforming the site for 3 more Na + Visit http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter6/animations.html See animation at Sodium-Potassium Exchange Pump (682.0K) Knowledged by Mr.Rupendra Shrestha

Active Transport:

Active Transport 3 main methods to move solutes against an electrochemical gradient Coupled transporters – 1 goes down gradient and 1 goes up the gradient ATP-driven pumps – coupled to ATP hydrolysis Light-driven pumps – uses light as energy, bacteriorhodopsin

Active transport:

Active transport Energy is required Knowledged by Mr.Rupendra Shrestha

Transporters are Linked:

Transporters are Linked The active transport proteins are linked together so that you can establish the electrochemical gradient Example ATP-driven pump removes Na + to the outside of the cell (against the gradient) and then re-enters the cell through the Na + -coupled transporter which can bring in many other solutes Also seen in bacterial cells to move H + Knowledged by Mr.Rupendra Shrestha

Active Transport:

Active Transport Energy coupling can transport against a concentration gradient Primary Transport is coupled to a chemical process (ATP hydrolysis) Secondary Transport is coupled to a favorable transport process

P-type ATPases - Active Transport:

P-type ATPases - Active Transport Transport phosphate coupled to ATP hydrolysis Inhibited by vanadate Na + K + ATPase 2K + out + 3Na + in + ATP --> 2K + in + 3Na + out + ADP + Pi Net charge (+1) transfer out results in a -50-70 mV membrane potential Energetically costly but membrane potential essential for action potential and other processes

F-type ATPases - Proton Gradients <==> ATP:

F-type ATPases - Proton Gradients <==> ATP Can either use ATP to pump protons or proton gradients to make ATP

ABC transporters - homologous family:

ABC transporters - homologous family classified by sequence and structure - not by function ATP dependent transport Multidrug resistance transporter pumps out foreign compounds The chloride channel CFTR responsible for cystic fibrosis Flippases for transbilayer lipid transport

Impacts, Issues: One Bad Transporter = Cystic Fibrosis:

Impacts, Issues: One Bad Transporter = Cystic Fibrosis Transporter proteins regulate the movement of substances in and out of cells; failure of just one of these proteins causes cystic fibrosis

Ion Gradients - Na+ or H+ can drive secondary transport:

Ion Gradients - Na + or H + can drive secondary transport lac permease - bacterial lactose proton symport Active transport of Lactose depends on maintenance of proton gradient

Na+- Glucose Symport in human intestine:

Na + - Glucose Symport in human intestine 2 Na + out + Glucose out --> 2 Na + in + Glucose in Combination of sodium chemical potential and membrane potential provide driving force for ~9000 fold concentration [Glucose] in /[Glucose] out

Ion selective channels:

Ion selective channels Ligand gated Acetylcholine Receptor Neuromuscular junction Voltage Gated K+ Channel

Ion channel measurements:

Ion channel measurements Patch Clamping can measure the characteristics of a single channel Glass micropipette can be used to capture a "patch" of membrane with one or more channels Patch detached from the cell - seals the pipet opening

Calcium Pumps:

Calcium Pumps Calcium is kept at low concentration in the cell by ATP-driven calcium pump similar to Na + -K + pump with the exception that it does not transport a second solute Tightly regulated as it can influence many other molecules in the cytoplasm Influx of calcium is usually the trigger of cell signaling Knowledged by Mr.Rupendra Shrestha

Calcium Pumps:

Calcium Pumps Moves Ca 2+ back into the sarcoplasmic reticulum (modified ER) in skeletal muscle

Coupled Transporters:

Coupled Transporters The energy in the Na + -K + pump can be used to move a second solute Energy trapped in the Na + gradient to move down its gradient and another molecule against its gradient Couple the movement of 2 molecules in several ways Symport – move both in the same direction Antiport – move in opposite direction Carrier proteins that only carry one molecule is called uniport (not coupled) Visit http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter6/animations.html See animation at Cotransport Knowledged by Mr.Rupendra Shrestha

Coupled Transporters:

Coupled Transporters Knowledged by Mr.Rupendra Shrestha

Na+-Driven Transport:

Na + -Driven Transport Na + driven symport. Used to move other sugars and amino acids Na + driven antiport. Also very important in cells Na + -H + exchanger is used to move Na + into the cell and then moves the H + out of the cell Regulates the pH of the cytosol Knowledged by Mr.Rupendra Shrestha

Na+-Driven Symport:

Na + -Driven Symport If one molecule of the transport pair is missing, the transport of the second does not occur

2 Methods of Glucose Transport:

2 Methods of Glucose Transport 2 mechanisms are separate Passive transport at the apical surface Active transport at the basal surface Caused by the tight junctions

Endocytosis Phagocytosis and Pinocytosis:

Endocytosis Phagocytosis and Pinocytosis Process by which plasma membrane engulfs & takes substances into cells Pac - man Knowledged by Mr.Rupendra Shrestha

Phagocytosis:

Phagocytosis Engulfing food particles Knowledged by Mr.Rupendra Shrestha

Endocytosis :

Endocytosis Phagocytosis ( pac - man eating) amoeba engulf food by flowing over & enclosing it. membrane forms a sac or vesicle which breaks off into interior of cell. Knowledged by Mr.Rupendra Shrestha

Endocytosis:

Endocytosis Pinocytosis- Pac-man drinking. Taking in of liquid droplets by engulfing them. Knowledged by Mr.Rupendra Shrestha

Endocytosis:

Endocytosis Receptor-aided endocytosis Steps: Receptor molecule binds to incoming substance. Forms an inward pit in cell membrane. Breaks off into a vesicle. Vesicle returns receptor to plasma membrane. Used to transport cholesterol. Knowledged by Mr.Rupendra Shrestha

Receptor Mediated Endocytosis:

Receptor Mediated Endocytosis (Figure 4-30, pg 102) Knowledged by Mr.Rupendra Shrestha

Exocytosis:

Exocytosis Reverse of endocytosis Used for expelling wastes, secreting substances Steps: Vesicle moves to plasma membrane, breaks open, releasing substance. Fuses with membrane Knowledged by Mr.Rupendra Shrestha

PowerPoint Presentation:

Knowledged by Mr.Rupendra Shrestha

Hope you enjoyed with seminar!:

Hope you enjoyed with seminar! Knowledged by Mr.Rupendra Shrestha Thank you all for Kind Attention!!!