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UCSD BIBC 102 - Midterm

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BIBC 102 Name_________________________________________________Midterm 10/31/02Student ID _________________________________________________page 1ENZYMES and KINETICS (10 points this page)A substrate S is converted into product P. When an enzyme is added to the reaction, the activation energyis lowered. Use single sentence answers for the following:1) What is the effect of addition of enzyme on the forward reaction (S to P) and the reverse reaction (P toS)?2) What is the effect of adding the enzyme on the equilibrium constant for S conversion into P?3) Suppose that the enzyme lowers the activation energy by 5kJ per mole. What letter best describes thechange in rate of the S to P reaction compared to when no enzyme is present?your choice: __________A) it is faster by a factor of e(5,000/RT) B) it is faster by a factor of (5,000/RT)C) it is slower by a factor of e(5,000/RT) D) the change depends on the original Eact Two versions (isozymes) of the same enzyme convert substrate S into product P. They each have the samekcat , but isozyme M (in muscle) has a Km of 5 uM and isozyme L (in liver) has a Km of 20 uM. Answerthe following questions about this situation.4) At what substrate concentration will M be half-saturated?5) What fraction (between 0 and 1) of saturation will enzyme M have at 20 uM substrate?6) What fraction of saturation will enzyme L have at 20 uM substrate?7) What is the ratio of maximal rates, Lmax/Mmax, for the two enzymes? (Think first…)8) (3 points) Write the general reaction for phosphorylation of an enzyme E. Use –OH to represent the Rgroup that actually receives the phosphate. Make sure to include all necessary substrates and products, andinclude the general name of the type of enzyme that catalyzes this reactionBIBC 102 Name_________________________________________________Midterm 10/31/02Student ID _________________________________________________page 2ENZYMES and KINETICS cont’ (10 points this page)The graph is a picture of a Lineweaver-Burk plot,, with data from two different enzymes, I and II, plotted.9) (2 points) In this sort of plot, each axis is a function of eithersubstrate concentration or rate. Indicate what each axis represent inthe space belowThe X (horzontal) axis is :The Y (vertical) axis is: 10) Which of the two enzymes, I and/or II,follows Michaelis-Menton kinetics? ______________11) (2 points) Why do you say the answer in 10)? (One sentence please)12) Where on this plot does one find the saturated rate for an enzyme? Write below please.Allosteric enzymes are often encountered in the study of metabolic regulation. Below is a simple rate plot,in rate plotted against substrate concentration S.Sketch in three curves, making sure to indicatewhich is which with labels.13) Draw a curve for a typical allosteric enzyme,label it E14) Draw a new curve for E when an allostericactivator is added, and label it A15) Draw a third curve for E when an allostericinhibitor is added and label it I16) What protein structural feature is nearly always associated with kinetic behavior of this sort?.[substrate]rateBIBC 102 Name_________________________________________________Midterm 10/31/02Student ID _________________________________________________page 3OXIDATION REDUCTION (10 points this page)17 (4 points) Glyoxylate can be oxidized to the two carbon, dicarboxylic acid oxalate. This is one sourceof the material in kidney stones. Starting with the structure of glyoxylate below, write a reaction for theoxidation of glyoxyate by NAD. Include any water or H+ you need to balance the reaction(Hey! These are the reactions from last year’s midterm! ) The following four half-reactions have thestandard reduction potentials listed.A) aKG + CO2 + 2H+ +2e isocitrate E’o = -0.38B) NO3- + 2H+ + 2e NO2- + H20 E’o = 0.421C) crotonyl-CoA + 2H+ 2e butryl-CoA E’o = -0.015D) Pyruvate + 2H+ 2e lactate E’o = -0.185There are 4 acceptors and 4 donors in this collection of reactions. Answer the following questions18) Which molecule in this collection of 8 (donors and acceptors) is the best oxidizing agent?19) Which molecule in this collection of 8 is the best reducing agent?20) List the letters for the reaction or reactions that would spontaneously reduce H+ ion at standardconditions21) (3 points) For reaction D, show the relationship between DE’o and the equilibriumconcentrations for this half reaction. Use letters for any constants (eg A for avogadro's number)CCO2OHBIBC 102 Name_________________________________________________Midterm 10/31/02Student ID _________________________________________________page 4An inborn error of glycolysis (10 points this page)One of the most powerful tools in the study of metabolism is use of radioactive atoms. The next questionswill use a labeled molecule to understand glycolysis in the cells of normal individuals, and those with aninherited disease.22) (2 points) 1-[14C]-fructose-6P is added to a cellular lysate with a fully functional glycolytic pathway.Draw a molecule of labeled pyruvate that would result from the labeled molecule ending up in that product.Just the pyruvate please…23) (2 points) Does every molecule of pyruvate derived from a labeled fructose have a labeled carbon?Yes or no, and explain your answerThere is a severe inherited disease caused by a null allele of the triose phosphate isomerase (TPI) gene.You know, the 5th enzyme of the glycolytic pathway. Homozygotes produce NO TPI enzyme activity.24) (4 points)Write the reaction that TPI catalyzes, including structures of reactant(s) and product(s)25) (2 points) 1-[14C]-fructose-6P is added to a cell lysate completely deficient in TPI, and glycolysis isallowed to proceed. Is there still label found in pyruvate? Why or why not?BIBC 102 Name_________________________________________________Midterm 10/31/02Student ID _________________________________________________page 5An inborn error of glycolysis (cont’) (10 points this page)26) (3 points) 1-[14C]-fructose-6P is added to a cell lysate deficient in TPI, what would you predict themain molecule with labeled 14C to be? Justify your answers with a picture and/or a sentence.When a molecule of glucose undergoes glycolysis in one of these cells that is completely TPI deficient, thebookkeeping or ATP profit changes in understandable ways. Let’s figure this out (so that you don’t haveto memorize it…).27)


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UCSD BIBC 102 - Midterm

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