Name Date Answers are provided on the last page of each homework assignment Grading policies can be found in our course syllabus in Canvas Briefly homework will sometimes be graded for completeness and neatness and sometimes for accuracy Your work must be handwritten your name and date must appear on each page You may work together but your answers must be in your own words Please submit an electronic copy of your handwritten work to HW5 Assignment in Canvas Homework submitted via email to the instructor or TAs will not be graded You must upload your work as a single PDF or DOCX file to Canvas to receive full credit Dissociation constants 1 A scientist analyzes the binding equilibrium for two proteins A and B that bind to the same ligand Both proteins have similar kon rates but they differ in their koff rates The scientist measured the concentration of the protein ligand complex at equilibrium for both proteins The same initial concentration of protein was used in both experiments and the concentration of the ligand was the same at equilibrium in both experiments She found that protein A had a protein ligand complex concentration double that of protein B at equilibrium Which of the statements below are true Briefly explain your reasoning for each statement i The binding constant for protein A binding to the ligand is larger than the binding constant for protein B binding to the ligand ii The Kd for binding of protein A to the ligand is smaller than for binding of protein B to the ligand iii The dissociation of protein A from the ligand has a smaller koff rate than for of protein B iv At equilibrium the experiment involving protein B had a larger concentration of free protein compared to the experiment involving protein A 2 For a protein ligand binding reaction the protein ligand concentration is measured to be 6 78 mM with 4 35 mM of unbound ligand remaining at equilibrium The initial protein concentration prior to the addition of the ligand was recorded as 12 45 mM Given these measurements calculate the Kd value for this reaction 3 Iron is essential for life In order to obtain iron from their environment bacteria and fungi rely on a class of compounds called siderophores One specific siderophore deferoxamine is used as a drug to treat iron overdoses that can result from genetic conditions or multiple blood transfusions Deferoxamine binds extremely tightly to iron and has a Kd of 10 31 M Assuming the kon rate constant for the reaction is typical of most protein ligand interactions what is the half life in seconds of deferoxamine iron complex Continued on the next page CHEM112B SP24 Homework Set 5 1 Name Date Enzyme inhibitors 4 Shown below is a binding pocket for a protein with a ligand bound The ligand interacts with a serine and a valine side chain a Briefly explain in terms of Kd the effect of a mutation that replaces the serine residue with a valine residue b Briefly explain in terms of Kd the effect of a mutation that alters the ligand as seen below binding to the original unmutated binding site 5 An inhibitor is added to an enzyme catalyzed reaction This inhibitor closely resembles the transition state that is formed in the course of the enzyme catalyzed reaction How would we expect this inhibitor to affect KM and Vmax 6 An enzyme catalyzed reaction is run and its Vmax and KM value are recorded An inhibitor is added at a concentration of 0 675 mM The value for KM did not change between the two reactions However Vmax decreased by 70 Continued on the next page a Where does this inhibitor bind to the enzyme Briefly explain b What is the value of Ki for the inhibited reaction CHEM112B SP24 Homework Set 5 2 Name Date Spontaneity 7 For each of the following processes indicate whether or not it is spontaneous based on your observation in daily life a A hot drink cooling to room temperature b Baking soda react with diluted white vinegar to form CO2 g at 25 oC and 1 atm c Decomposition of N2 g to form N g at 298K and 1 atm d Combustion of natural gas 8 Which of the following processes are both spontaneous and endothermic Select all that apply I Water freezing at 10 C II Activation of an instant cold pack that mixes ammonium nitrate with water III The sublimation of dry ice at room temperature 9 Consider the evaporation of water at 1 atm a At what temperature is this process spontaneous b At what temperature is it non spontaneous c At what temperature is it reversible d Is the process exothermic or endothermic 10 Which of the following statements is are true I A spontaneous process is reversible II A spontaneous process is at equilibrium III A spontaneous process can do work IV If a process is spontaneous at one temperature it will be spontaneous at all temperatures Review Heat of reactions and Enthalpies of formation 11 Write the balanced chemical reactions for the formation of one mole of each of the following compounds from its elements in their standard states Use the eBook Data Table Thermodynamic Data Organic and Thermodynamic Data Inorganic to find the corresponding H f values a solid barium carbonate BaCO3 s b gaseous ammonia NH3 g c aqueous sulfuric acid H2SO4 aq d liquid methanol CH3OH Continued on the next page CHEM112B SP24 Homework Set 5 3 Name Date 12 Using the Hf values from the table below calculate H rxn for the following reaction 4 NH3 g 5 O2 g 4 NO g 6 H2O Substance Hf kJ mol H2O NO g NO2 g HNO3 aq NH3 g 286 90 34 207 46 H f for H2O g 241 9 kJ mol H f for CO2 g 393 5 kJ mol Answers are provided on the next page 13 The combustion of 1 mole of 2 3 4 trimethylpentane C8H18 to CO2 g and H2O g produces 5069 kJ of energy Given the information below what is H f of 2 3 4 trimethylpentane CHEM112B SP24 Homework Set 5 4 Name Date Answers 1 All of the statements are true 2 3 64 mM 3 6 93 1023 seconds or 2 2 1016 years 4 a Kd will increase b Kd will decrease 5 Vmax will stay constant KM will increase 6 a A site other than the enzyme s active site b 0 289 mM 7 a b and d are spontaneous c is nonspontaneous 8 II and III only 9 a This process is spontaneous above 100 oC b This process is non spontaneous below 100 oC c This process is reversible at equilibrium at 100 oC d This process is endothermic under all temperatures Ba s C s 3 2 O2 g BaCO3 s Hrxn 1216 3 kJ N2 g 3 2 H2 g NH3 g Hrxn 46 11 kJ H2 g S s 2 O2 g H2SO4 aq Hrxn 909 27 kJ C s 2 H2 g O2 g CH3OH Hrxn 238 66 kJ 10 …