22. Chromatographic Methods Three polypeptides, the sequences of which are repre

Question

22. Chromatographic Methods Three polypeptides, the sequences of which are represented below using the one-letter code for their amino acids, are present in a mixture: 1. ATKNRASCLVPKHGALMFWRHKQLVSDPIL QKRQHILVCRNAAG 2. GPYFGDEPLDVHDEPEEG 3. PHLLSAWKGMEGVGKSQSFAALIVILA Of the three, which one would migrate most slowly during chromatography through charged groups? charged groups? (a) an ion-exchange resin, beads coated with positively (b) an ion-exchange resin, beads coated with negatively c) a size-exclusion (gel-filtration) column designed to separate small peptides such as these? (d) Which peptide contains the ATP-binding motif shown in the following sequence logo? 4 0 1 23 4 5 6 78

Explanation / Answer

a) positively charged resin will arrest negative AA, HENCE, 1 will migrate most slowly

b) negatively charged resin will arrest positive AA, Hence, 2 will migrate most slowly

c) 2, being smallest will be arrested by the resin and hence will migrate slowest

d) The logos are read as follows, the letters represent AA and numbers on the x-axis the position, relative positions represent conservation at that position. Sequence three positions 9-16 has a similar sequence as the motif represented by the logo. You can detect it by looking at 1st(G), 6,7, and 8th letters (GKS)

Number of AA Positively charged (DE) Negatively Charged (RKH) Net Charge (in terms of AA) 1 1 10 -9 2 6 1 +5 3 1 3 -2

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