Membrane Transport

Membrane Transport Hydrophobic molecules Membrane structure results in selective permeability ;some substances cross more easily than others The plasma membrane controls the exchange of materials between the cell and its surroundings Transport Proteins HO 2 lipid bilayer and pass through the membrane rapidly • Urea Glycerol The hydrophobic interior of the membrane impedes gf the passage of hydrophilic (polar) molecules large uncharged polar molecules Bo Glucose Sucrose Transport proteins move only specific substances For example, glucose carrier proteins only , transport glucose; they will not transport fructose The selective permeability of a membrane is dependent on both the Carrier proteins bind to molecules and change shape to shuttle them across the membrane Ions t t t H Na K HCO j Cl Ca get at Mg - . lipid bilayer and the specific transport proteins it contains I Hydrophobic regions Channel proteins have a hydrophilic channel that certain molecules or ions can use as a tunnel Passive transport High concentration Facilitated Diffusion Hydrophilic regions Active transport needs energy No need for energy Bd Low concentration Low concentration Uses proteins but no usage of energy channel proteins and carrier proteins In facilitated diffusion,transport proteins speed the usually in the form of ATP hydrolysis to move solutes against their gradients the movement of particles of any substance so that they spread out evenly into the available space passive movement of molecules across the plasma membrane All proteins involved in active transport are carrier proteins This change in shape can be triggered by the binding and release of the transported molecule S S sodium-potassium pump Like the sodium- potassium pump but Substances diffuse down their concentration gradient without any usage of energy Channel proteins 2 Bh pm Ion channels facilitate the transport of ions At r a s h + Cytoplasmic Na Binds to the Some ion channels, called gated channels, open or close in response to a stimulus Aquaporins facilitate the diffusion of water + . sodium-potassium pump. stimulate phosphorylation by a kinase using ATP high affinity to Na t Selectively permeable membrane B. The sugar molecules Osmosis Binding of 3 Na ions In this shape the protein has potassium ion channels in nerve cells open in response to electrical stimulus ; Other gated channels open in response to chemical stimulus • High concentration * Active transport requires energy, Diffusion Carrier proteins Carrier proteins under go a subtle shape change that moves the solute-binding site across the membrane Hydrophobic (nonpolar) molecules dissolve in the DO O2 CO2 N2 Benzene Small uncharged polar molecules can’t pass the membrane G The phosphorylation leads to change 2K are released and again the protein in protein shape reducing its affinity has high affinity to Na t is the diffusion of free water for Na, so the 3 Na are released + The loss of phosphate concentration to the region of higher solute concentration t 2K bind to the protein * protein to its original and trigger the release of shape which has Lower the phosphate group affinity for K + unaffected by the concentrations of other substances 3 at has high affinity to K, so group restore the Each substance moves down its own concentration gradient Free water molecules diffuse from the region of lower solute + The new protein shape • Tonicity g Membrane potential is the voltage across a membrane the ability of a surrounding solution to cause a cell to gain or lose water Voltage is created by differences in the distribution of positive and negative ions across a membrane electrochemical gradient drive the diffusion of A solution is hypotonic if the solute concentration is less than that inside the cell Water moves from surroundings to the inside of the cell (Normal ) – A chemical force (the ion’s concentration gradient) – An electrical force (the effect of the membrane potential on the ion’s movement) hypertonic An electrogenic pump is a transport protein that generates voltage across a membrane, storing energy that can be used for cellular work A solution is isotonic if its solute concentration A solution is hypertonic if the solute is the same as that inside the cell concentration is greater than that inside the cell Water diffuses across the membrane at the same rate in both directions; there is no net movement So passive transport of cations is into the cell, and anions is out of the cell ions across a membrane Animal cell isotonic The inside of the cell is negative in charge relative to the outside An ion diffuses down its electrochemical gradient Two combined forces called : Tonicity depends on the concentration of solutes in the solution that cannot cross the membrane, relative to that inside the cell hypotonic • An Water keeps moving until the solute concentration is equal on both sides BBA An electrogenic pump is a transport protein that generates voltage across a membrane, storing energy that can be used for cellular work animals main pump is the sodium-potassium pump Plant cell plants, fungi, and bacteria main pump is the proton pump Cotransport Water moves from the inside of the cell to the surrounding hypotonic isotonic hypertonic 7 ② occurs when active transport of a solute indirectly drives transport of other substances (Normal ) Plant cells use proton pumps to generate an H+ gradient across the cell membrane . This is how plants load sucrose into their veins for transport around the plant body Animal cells use a similar cotransporter to couple the active transport of glucose to the diffusion of Na+ into cells lining the intestine ' Cells with out cell walls will gain water,swell and lyse (burst) The volume of a cell without a cell wall is stable in an isotonic solution Cells with out cell walls will lose water,shrivel,and likely die in hypertonic solution . . Normally,sodium in waste is reabsorbed in the colon to maintain a constant level in the body When a person has diarrhea, waste is expelled too fast for reabsorption, causing sodium levels to drop Drinking a concentrated salt (NaCl) and glucose solution enables uptake through the Na+/glucose transporters in the intestine A rapid drop in sodium can be life-threatening Steps : I Active transport of H against its radiant energy “ uphill “ with ATP • the movement of H + Diffusion of H back down its concentration gradient “ downhill “ couples the active transport of sucrose into the cell