Estimate the flux (mg/cm2/s) by diffusion of estrogen (a steroid) through a lipid bilayer cell membrane when assuming the diffusion coefficient for estrogen across the lipid bilayer is 10^–6 cm2/s, and that the initial concentration of estrogen in the extracellular fluid is 1 ng/mL and 0 in the cytoplasm.

The uptake of l-ascorbate (vitamin C) and its oxidized form, dehydro-l-ascorbic acid (DHAA), was evaluated in brush border membrane vesicles isolated from adult human small intestine. Ascorbate uptake was Na+-dependent and potential-sensitive (Km, 200 umol/L), whereas DHAA transport occurred through Na+-independent facilitated diffusion (Km, 800 µmol/L). If the Vmax of vitamin C import through channels is 401µmol/min/cm2, what import rate would you expect if the lumen contained 133 µmol/L of the version of vitamin C that moves through them?

Suppose that certain cells found in an organism are permeable to both CI" and Kt ions but no other ions at rest. The intra- and extracellular concentrations of both ions for these cells are shown below. The resting membrane potential is -75 mV. Assume that passage of both ions across the membrane occurs through ion channels that are selective for each ion. [Intracellular] [Extracellular] CI 4 mM 110 mM K+ 25 mM 100 mM Based on this information, what reasonable conclusion can you draw about the relative permeabilities of K* and CI" ions in these neurons at rest based on what we discussed? а. The membrane is more permeable to chloride ions than to potassium ions at rest. b. The membrane is more permeable to potassium ions than to chloride ions at rest. С. At rest, the membrane potential of these neurons lies closer to the potassium equilibrium potential (EK) than it does to the chloride equilibrium potential (ECI). d. Both a and c е. Both b and c

Below find the structures for ibogaine and cocaine. Ibogaine and cocaine inhibit the dopamine active transporter (DAT).  This transporter is a secondary active transporter, and depends on the primary active transporter Na+/K+ ATPase.  Ibogaine had a Kι = 2 μM, and cocaine a Kι = 0.64 μM respectively. (a) Define secondary active transport. (b) Is ibogaine an effective treatment for cocaine based on DAT binding?

A one-to-one protein (P)-ligand (L) complexation (P + L PL) has a dissociation equilibrium constant (Kd) value of 100 nM at 25°C, and the Kd remains the same at 37°C. 1) What is AS of binding at 25°C? Assume ACp of the binding is 0 over the temperature range. AS = 1.34E2 kJ/(mol*K) (note the unit!!) (sig. fig =3) 2) What is the concentration of the PL complex formed at equilibrium when you mix 0.20 uM (microM) of Protein and 1.0 uM of Ligand together at 37°C? PL at equilibrium = 8.1E-1 uM (note the unit!!) (sig. fig =2)

If a skeletal muscle has depleted its stores of ATP how will the altered transport properties of the following transporters affect cytosolic ion concentrations (increase, decrease, no change) relative to normal?   Skeletal Muscle Cell With Depleted ATP Stores Ion transporter Cytosolic K+ Cytosolic Na+ Cytosolic Ca2+ NKA         NCX         SERCA

You have a semi permeable membrane with a membrane potential of -90mV. You also have two ions that are both permeable to the membrane, Na and Cl. Na has a concentration of 10mM inside the membrane and 120mM outside the membrane. Cl has a concentration of 1.5mM inside the membrane and 77.5mM outside the membrane. Use the nernst equation to calculate the electrochemical equilibrium of both ions, and show in which direction the netflux would be for each ion.

In the experimental conditions described below, how many molecules of dextrose do you have to add to the extracellular fluid in order to make it iso-osmotic relative to the intracellular fluid? Intracellular fluid: Number of water molecules = 60 • Number of Dextrose molecules = 7 • Number of Sucrose molecules = 3 ● Extracellular fluid: • Number of water molecules = 160 • Number of dextrose molecule = ???? • Number of Sucrose molecules = 0

Calculate ΔGinward. Is energy required for transport to happen?  The cell is at 25°C. Membrane potential = -60 mV. What is the ΔGinward for chloride? Use the chart.

(b) The GLUT system is highly selective for glucose. It also speeds up the rate of glucose transport across the membrane by as much as 100-fold when compared to the passive diffusion of glucose across a bilayer in the absence of any transport system. While impressive, this rate of transport is much slower than purely diffusion limited rate of movement (ie. the fastest a molecule can move by diffusion). Given this fact, on the blank plot below draw the expected relationship between the rate of GLUT-mediated transport and increasing [glucose]? Use the space below the graph to explain your answer. fast Transport Rate slow low [glucose] high (c) Next, use a dashed line on the same plot above to draw the shape of the curve when the amount of GLUT transporters in the membrane is cut in half. Briefly explain your answer in the space provided below the graph.