BIO320_HW1_2010_answers

BIO320_HW1_2010_answers - Name _ Due Tuesday February 2nd,...

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Name _____________________________________ BIO320 HW-1 (20 points) Due Tuesday February 2 nd , 2010 Please turn in your printed copy to class Please write legibly, preferably by computer Problem 1) The resolving power of a light microscope depends on the width of the cone of light that illuminates the specimen, the wavelength of the light used, and the refractive index of the medium separating the specimen from the objective and condenser lenses, according to the formula: resolution = 0.61 λ n sin θ where λ equals the wavelength of light used, n is the refractive index, and θ is half the angular width of the cone of rays collected by the objective lens. Assuming an angular width of 120° ( θ = 60°), calculate the various resolutions you would expect if the sample were illuminated with violet light ( λ = 0.4 µ m) or red light ( λ = 0.7 µ m) in a refractive medium of air (n = 1.00) or oil (n = 1.51). Which of these conditions would give you the best resolution? Answer : Substituting values into the equation, the resolution for violet light in air is 0.28 µ m and in oil is 0.19 µ m. The resolution for red light in air is 0.49 µ m and in oil is 0.33 µ m. Clearly the best resolution is obtained with violet light (0.4 µ m) using oil immersion (n = 1.51), as calculated below: resolution = (0.61)(0.4 µ m) / (1.51)(sin 60°) = 0.19 µ m Problem 2) You hate the smell of mercaptoethanol. Since there are no disulfide bonds in intracellular proteins, you have convinced yourself that it is not necessary to treat a cytoplasmic homogenate with mercaptoethanol prior to SDS-PAGE. You heat a sample of your homogenate in SDS and subject it to electrophoresis. Much to your surprise, your gel looks horrible; it is an ugly smear! You show your results to your friend who is a chemistry major, and she suggests that you treat your sample with N-ethylmaleimide (NEM), which reacts with free sulfhydryls. You run another sample of your cytoplasmic homogenate after treatment with NEM and SDS. Now the gel looks perfect! If Intracellular proteins don’t have disulfide bonds (and they don’t) why didn’t your original scheme work? And how does treatment with NEM correct the problem? Answer
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This note was uploaded on 04/12/2010 for the course PSY 339 taught by Professor Neal during the Spring '09 term at University of Texas at Austin.

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BIO320_HW1_2010_answers - Name _ Due Tuesday February 2nd,...

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