GRE Subject Question

At what pH would an amino acid bear both a COOH and an NH2 group, and why?

GRE Biochem question

The galactose represser protein from E. coli has a pI of about 5.9. While purification protocols were being designed, it was found to bind to a Mono-S column at pH values of 7 and below. (Mono-S columns have S-type sulfonic acid groups attached to the resin and are strong cation exchangers.) What is unusual about this observation, and explain these results?

GRE subject Question

The table below indicates approximate values for these at 25C. For reference, the delta H(ionization) for Tris is 47kJ/mole. Group deta H (ionization)(kJ/mole) Asp 3.9 Glu 0 Lys 48 Arg 48 His 28 N-term 40 C- term 0 How will the net charge of a typical protein change upon lowering the temperature from 37C to 4C, based on this information? What can be done experimentally to compensate for this?

GRE subject exam

Normal Human Hemoglobin (HbA) P50 = 26 torr and the hill coefficientis N= 2.8 You Have obtained the following oxygen binding curvedata on a new sample of human hemoglobin. A) is this sample normal? (This can be solved by visual inspection) po2 log(po2) Theta theta/1-Theta) Log(theta/1-Theta) 10 1.000 0.0039 0.0039 -2.4089 20 1.301 0.0588 0.0625 -1.2041 30 1.477 0.2404 0.3164 -0.4998 40 1.602 0.5 1.0000 0.0000 50 1.699 0.7094 2.4410 0.3876 60 1.778 0.8351 5.0630 0.7044 70 1.845 0.9037 9.3790 0.9722 80 1.903 0.9412 16.0000 ... click for more

BIOCHEM GRE Subject Question

You have been investigating a membrane protein that appears to have seven 24 residue transmemebrane Alpha helices. Assume that each helix is perpendiculiar to the plane of the membrane and goes exactly from side of the membrane to the other. Also assume that each helix is linked to the next by a loop with a minimun of 12 amino acid residues. A) From typical helix parameters and the information given, estimate the thickness of the membrane? B) What is the minium number of residues in this protein? C) Using the result of B) estimate the molecular weight of this protein? D) How many mainchain H-bonds are in each helix? E) What types of amino acids residues do you expect to make... click for more