In this problem, we are asked to draw a slab gel for four proteins:
2) Hemoglobin B
3) Hemoglobin A
A slab gel will separate proteins based on their molecular weights - the heavier proteins will travel slower and thus less distance. A quick perusal of these proteins shows that myoglobin is the heaviest, followed by hemoglobin B and then hemoglobin A.
Thus, the slab gel will appear approximately as follows:
In this problem, we are asked to explain which methods of analysis are used in the experiment to determine the purity of the a-lactalbumin purified from the milk.
The process uses two chromatography steps (Sephadex [size exclusion] and affinity), and two different assays - SDS-PAGE and the Bradford Protein Assay. Chromatography is the method by which we purify, but it does not tell us the level of purity attained.
The Bradford assay is a subjective assay that tells us how much protein we have in a sample, but the SDS-PAGE separates the samples into their component proteins, which will tell us the the purity of our post-chromatography material.
In this problem, we are asked to state which amino acid residues bind the affinity column's immobilized metal ions.
The metal ion in the affinity column presents a positive cation for coordinating bonds with molecules that have electrons to donate. Conjugated ring systems are one such structure found in protein residues, specifically the imidazole ring in histidine and the indole ring in tryptophan. Sulfa groups such as the sulfahydryl group in cysteine also qualify.
Any residue with electron-donating groups (HIS, TRY, CYS, SER, and others) can be bound by the metal ions of the affinity column.