GRE exam question

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 quartenary 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... click for more

GRE subject Question

Biochemists generally like to study and characterize proteins as pure substances isolated from their native enviroment. What is the single most important method or procedure that must be availible prior to starting the purification of a protein?

GRE subject Question

You have isolated and purified a a small octapeptide protein and want to determine its primary structure. Deduce the sequence from the following experimental results. A) Complete amino acid analysis, corrected for amino acid hydrolysis loss yielded the following composition (Arg, Glu, Lys, Met, Ser, Thr, Trp, Tyr) B) Reduction with Dansyl Chloride followed by acid hyrolysis and separation yielded the following dansylated compound.: Dansyl Chloride with an attached R group of (CH2OH) C) Chymotrypsin yielded three fragments , a pentapeptide, a dipeptide containing Tyr, and the single amino acid Glu: D) Reaction of the original polypeptide with CNBr produced two tetrapeptides. R... click for more

GRE subject Question

Shown Below is a helical wheel projection of one of the Alpha helices from human hemoglobin. This is an amphipathic helix with one side polar and exposed to solvent and the other side nonpolar and buried. Indicate approximately which side of the helix is likely to be in the solvent exposed and which side is likely to face the hydrophobic interior of the protein. What is the most reasonable candidate for a terminal residue in this alpha helix ( in this case it is the C-terminus) WHY?

GRE Subject Question

Insulin consists of two peptide chains, a shorter A-chain and a longer B-chain. The two chains are held together with disulfide bonds. Invivo, insulin is processed from a single polypeptide chain called proinsulin by specific protease. Processing involves removal of the C-chain from proinsulin as indicated below. A denaturation/renaturation experiment, similar to the one carried out by Anfinsen on ribonuclease, was performed. In contrast to his results, less than 10% activity was recovered upon removal of 2-Mercapoethanol and Urea. When the experiment was repeated on proinsulin , full activity was restored. PLEASE EXPLAIN?