The steroid progesterone has an important role in the female reproductive system. Researchers interested in studying membrane progestin receptors (MPRS) developed a method to produce and purify the protein in active form. First, the researchers devised a way to prepare a specific MPR known as hMPRA using the machinery of yeast cells. In order to facilitate purification and identification in later studies, they manipulated the yeast cells so that they attached two different tags to the C-terminal end of the protein. The first tag, Compound 1, is a peptide sequence that acts as an epitope, part of a much larger peptide sequence that is recognized by the immune system. The second sequence consisted of six consecutive histidine residues (His). This sequence binds tightly to Ni2+ cations. In chromatography, (His), tag labeled proteins can be eluted from Ni²+. supported columns by adding a small molecule to the eluent that mimics the side chain of histidine. After preparing hMPRA, the researchers conducted a binding assay that utilized tritium labeled 1,2,6,7-[H³]-progesterone to measure the K of the receptor while still in the membranes of the yeast cells. hMPRA was then extracted from the membranes using n-decyl-B-D-maltopyranoside, Compound 2. The researchers purified the hMPRA with two successive rounds of chromatography that exploited each of the tags. The buffers used to elute the protein contained 300 mM NaCl, 50 mM NaH₂PO4 (pK, = 7.2), and various amounts of NaOH (MM = 40 g/mol). During the first chromatography step, a specific chemical agent was immobilized on the stationary phase to bind to the Compound 1 tag. After the second chromatography step, which utilized the (His), tag, the researchers used the same binding assay and found that K, was similar. Adapted from M. B. Hossain, T. Oshima, S. Hirose, J. Wang, and T. Tokumoto, "Expression and Purification of Human Membrane Progestin Receptor a (mPRA)." PLOS One. ©2015 Creative Commons Attribution. A major obstacle to obtaining useful energy from a nuclear fusion reactor is containment of the fuel at the very high temperatures required for fusion. The reason such high temperatures are required is to: O A. eliminate the strong nuclear force. OB. remove electrical charge from reactants. O C. decrease the density of the fuel. D. enable reactants to approach within range of the strong nuclear force. Glu-Gin-Lys-Leu-Ile-Ser-Glu-Glu-Asp-Leu Compound 1 Blood flows with a speed of 30 cm/s along a horizontal tube with a cross-section diameter of 1.6 cm. What is the blood flow speed in the part of the same tube that has a diameter of 0.8 cm? O A. 7.5 cm/s O B. 15 cm/s O C. 60 cm/s OD. 120 cm/s Consider the fully protonated amino acid shown. II OA. I OB. II O C. III O D. IV As the pH of a solution of this amino acid is raised, which group deprotonates first? Energy HOT CICI NH3 O A. 2g/7 OB. 3g/7 O c. 5g/7 OD. g The graph represents the energy change in an exothermic reaction: A+B+C O A. E₂-E₁ OB. E₂-E₁ O C. E₁-E₂ OD. None of the above E3 A + B E₂ E₁ OH Reaction IV Which of the following expressions gives the activation energy for the reaction? III A 2 kg mass and a 5 kg mass are connected by a massless cord suspended over a massless and frictionless pulley. If the acceleration due to gravity is g, what will be the acceleration of the masses after they are released from rest? An ice cube at 0°C and 1 atm is heated to form steam at 100°C and 1 atm. Ignoring heat loss to the surroundings, what part of the process uses the most heat? O A. Melting the ice cube OB. Heating all the water from 0°C to 50°C OC. Heating all the water from 50°C to 100°C O D. Vaporizing all the water (Note: Specific heat of water = 1 cal/g°C. Heat of fusion = 80 cal/g. Heat of vaporization = 540 cal/g.)