The diffusion coefficient for a lipid in a membrane bilayer is 1.0  10-9 m2s-1. How long (s) will it take for a lipid to diffuse a linear distance of 10 nm in the bilayer (298 K)?

a. You selectively label phospholipids with a fluorescent dye and perform the FRAP assay. You detect a single fluorescence molecule move 100 micrometre into the photobleached area in 2.5 seconds. What is the diffusivity constant for this phospholipid? b. Increasing the ratio of unsaturated to saturated phospholipids in a biological membrane increases membrane fluidity. Describe how the FRAP photobleaching and recovery curves would differ between membranes with 63% and 41% unsaturated phospholipids. c. Draw the FRAP photobleaching and recovery curves for your answer in b. d. What does the “immobile fraction” in a FRAP experiment suggest (see diagram)?

Acetic acid (a weak acid with a pKa of 4.75) and ethanol (an alcohol) are each composed of two carbons, hydrogen, and oxygen, and both enter cells by passive diffusion. At pH 7, one is much more able to permeate a cellular membrane than the other. Which is more membrane permeable, and why? Predict how the membrane permeability of each is altered when the extracellular pH is reduced to 1.0, a value typical of the stomach.

Molar concentration 1.0 Molar concentration Depicted below is a cell membrane separating two closed compartments, each filled with one liter of H₂. You add one mole of each of the molecules as shown below. The molecule to which the membrane is most permeable diffuses across at a net rate of 0.5 moles/hour. Based on this information, answer the following questions. 1.0 0₂ Nat 0.5- fructose glycerol K+ 2. Graph the expected relative concentrations of each solute in the right hand compartment as a function of time. 1 Time in hours Nat 1. Immediately after adding these solutes, will there be a net movement of H₂O molecules across the membrane in one direction? If so, in which direction and why? through right K+ 3. Finally, you add ATP to the left side compartment at the time indicated by the arrow below, and measure concentration of Nat and K+ in the right side compartment. Your results are graphed below. Propose a hypothesis to explain the results you obtained in this experiment. 2 (10…

Diffusion and Osmosis What is your prediction about the effect of molecular weight on rate of diffusion? What is your prediction about the effect of temperature on rate of diffusion?

The antibiotic Gramicidin A can transport Na+ inons into a certain cell at the rate of 5.0 x 10 ^7 Na+ ion channel-1 s-1. Calculate the time in seconds it takes to transport enough Na+ ions to increases its concentration by 8.0 x10 -3 M in a cell whose intracellular volume is 2.0 x 10-10 mL

0.4 osM 0.3 osM True or false about the diagram where a cell is placed into the 0.4 osM solution: the biological membrane acts as a semipermeable membrane OTrue False

Your research advisor would like you to measure the movement of a protein X using FRAP. The results of your FRAP experiment are shown below. What can you conclude? Fluorescence Intensity (Arbitrary Units) Time (Seconds) Time point of exposure to an intense laser Protein X appears to be completely immobilized in the membrane Protein X appears to be partially immobilized in the membrane You cannot make predictions about the mobility of Protein X with these data Protein X appears to be completely mobile in the membrane

17. Muscle. Contractions which move the body depend heavily on diffusion. Why do we have difficulty moving our fingers etc. when they are cold ?

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)