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It is not strictly required. Isotope labelling is required when the usual isotope does not have a magnetic spin (for example 12C). 14N has a spin of 1 and exhibits 3 spin states: -1, 0 and 1. The isotope, 15N has a 1/2 spin. As noted in this book, analytical methods exist for both nitrogen isotopes. However, 15N is preferred for NMR studies because the ...


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In the biological context, membrane-partitioning is usually referring to the stage in which the transmembrane-destined region of a protein moves from interacting with the water, to interact with the interface of the membrane. In the diagram below showing a four step thermodynamic cycle, the partitioning free energy can be referred to as as ΔGwiu in terms ...


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An SDS-PAGE standard curve of Rf vs LogMW is linear because the standard you're given is engineered to behave that way. An expanded SDS-PAGE curve would show that the actual graph is sigmoidal: Structues that are too large can't enter the matrix, and too small they pass right through. Your standard has taken into account the % composing the gel, and the size ...


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I think Feynman is referring to the second law of thermodynamics. The entire statement is this: The most important feature of the cycle of Fig. 3–1 is the transformation from GDP to GTP (guanosine-di-phosphate to guanosine-tri-phosphate) because the one substance has much more energy in it than the other. Just as there is a “box” in certain enzymes for ...



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