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    Considering Protein Structure

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    You have isolated a new protein and are in the process of characterizing it. Several pieces of data about the protein are presented below. What can you deduce about the structure of this protein at primary, secondary, tertiary, and quaternary levels.

    A) The protein elutes in a void volume on a gel filtration column with a fractionation range of 30kDa to 300kDa

    B) SDS-PAGE(reduced) shows the protein has three bands with molecular weights of about 215, 18, and 22kDa.

    C) Following brief treatment of the original protein with chymotrypsin, the resulting protein sample now elutes from the gel filtration column as two peaks (250, 130kDa)

    D) The 250kDa sample from C) runs as a single band at 125kDa on SDS PAGE (reduced) SDS PAGE (reduced) of the other sample from C) shows it to contain 3 bands 90,22, and 18kDa

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    Solution Preview

    Let's look at what we can conclude from each piece of data, and then describe the protein structure. Keep in mind the conditions under which each result was obtained: was the protein in its native conformation? Or was it denatured or reduced such that tertiary or quaternary structures were disrupted?

    A) A gel filtration column separates protein on the basis of size. Larger proteins elute from the column first, while smaller proteins elute later because they can penetrate the porous matrix. The void volume refers to the volume of the column itself. So a protein that eluted in the void volume must be larger than the maximum size of protein filtered by the matrix; it was too larger to enter the porous matrix. Since this particular column will separate proteins up to a size of 300 kDa, our ...

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