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exam queftion exchange Name That Compound, Part II
J.
ALEXANDER
University ot Cincinnati Cincinnati. Ohio 45221
Therefore, the formula is either
A. Mancott
I. A~B&D,sE, or 11. ABfiC,sD,E,
Queensboraugh Community College Bayside. NY 11364
This problem requires the use of algebraic reasoning to derive and solve a diophantine equation whose parameters are restricted to being integers. After the parameters have been ascertained, use the concepts of moles and formula weight to determine which one of the answers is applicable to the solution of the prohlem. In addition, the concept of entropy and knowledge of qualitative analysis and nomenclature are required. Question
A mole of the compound A,BbC,DdE, was found to (1) have a formula weight of 467 (2) contain a total of 34 g-atoms, of which b = e, d = 3a, and c =
3b. Element B when reacted with excess oxygen forms a compound whose common name is after-damp. Element C forms a cation having an So = 0.00. Element D was discovered by Alhertus Magnus, and its cation is identified by the Gutzeit test. Element E when present in a compound cannot he determined by any qualitative test. What is the name of compound A.BbC,DdE,? Acceptable Solution
a+b+e+d+e=34
JOHN
Element D is arsenic (atomic weight = 75). The grams of arsenic in formula l is This weight is greater than the formula weight of the compound, whichis 467. Therefore, I1 is the correct formula,and thecompound now has the formula AB6C18A~3Es. Element B is carbon (atomic weight = 12). After-damp is the common name for COz. Element C is hydrogen (atomicweight = 1.0).So = 0.00 for Hi. Element E is oxygen (atomic weight = 16). Thereisnoqualitative test todetermine the presence ofoxygen in a compound. The compound now has the formula AC6H1&s306. Grams of A in the compound = 467 - [(6)(12) + (18)(1.0) (3)(75)+ (6)(16)1= 56. Atomic weiehtof A = 5611 = 56. ElementA is iron. The campound now has the formula FeC6HlaAssOs,which is Fe[ ( C H ~ Z A S Oferric ~ ] ~ .or iron (111) dimethyl metarsenite.
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Metabolic Questions Hugh A. Akers
(1)
Place values of statement (2) into eq 1. a+b+3b+3a+b=34 Combine terms to form the diophantine equation: The parameters a and bare restricted to being integers. Therefore, let b equal 1 through 6 and solve for the values of a. Two sets of integers for a and b meet the above criterion when I. b = 2, a = 6 and 11. b = 6 , a = l
Lamar University Beaumont. TX 77710
Intermediary metabolism for many consists of glycolysis and the citric acid cycle. In addition to the intermediates, students are often expected to know enzyme names, inhihitors, weights, control mechanism, kinetic parameters, and to he able to return this information on examination. For others,. enzvme . mechanisms. cofactor involvement. energy runsidern~i~mr, and rhr interrelationships between thc rmthwn\.s is the ubiect of studvinr inrerrnediar\f rnetabolisk. ~ l y c i l y s i sand t h e citric i c i i cycle do ndt provide sufficient examples and comparisons so, to the students'
chagrin, more pathways are covered (e.g., those involving amino acids). A maior problem is encountered when examination time comes:-how to test the students if they are not expected to know the pathways verbatim? The following method has proven successful for the last two years. The basic approach is to outline a metabolic pathway to which the student has not been exposed. The student is asked to construct themetabolicpathway from a description of a seauence of events and to identifv (loeical). cofactors that are anticipated to be utilized. Addition questions can involve enzvmes. Anv structures unfamiliar to the student can he provided in thk question. This type of question allows the continuation of teaching while testing. T h e students find the puzzle nature of these questions to be a challenge since they require performance a t the synthesis level. Some examples follow. Quesllons 1. Several pathways exist in different organisms for the metabolism of nronionvl-CoA. Most oreanisms utilize the . . . pathway that feeds into the citric arid cycle via surcinylCoA. Another metillx~licroute nsrd IIV ('losrridium k l u l veri is a "continuation of B oxidation' and consists of the following enzymatic reactions: (a) propionyl-CoA is converted to acryloylCoA; (h) formation of 3-hydroxypropionyl-CoA; (c) conversion to malonyl semialdehydeCoA, (d) production of malonyl-CoA, which is then (e) decarboxylated to produce acetyl-CoA. Outline theabove steps between propionyl-CoA and acetyl-CoA. Show structures for the metabolites and indicate appropriate cofactors (free or hound) that may he involved. Suggest a mechanism for enzyme reaction (e).
2. In Bacillus subtilis threonine is metabolized bv the following sequence of reactions: (a) oxidation; (h) decarboxvlation: (c) transamination: then. (d) oxidation to ~ r o duce pyruvate. Outline this sequence of steps, show the structures of the substances, use abbreviations for the cofactors, and show any enzyme-hound coenzymes. What type of enzyme-bound intermediate is likely for reaction 3. In Clvstridium tetanomorphum glutamate is fermented by the following reaction sequence: (a) glutamate is converted to O-methylaspartate (2-amino-3-methylsuccinate); (b) ammonia is released by an elimination reaction to produce mesaconate {trans-HO,CCHC(CH,)CO,H);
(c) mesaconate is hydrated; and (d) the last reaction involves the cleavage to pyruvate and acetate. Outline the above pathway, show structures, and indicate any cofactors (free or enzyme hound). Suggest a mechanism for reaction (d).
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Acceptable Solutions 1. (a) CH&HzCO-CaA + FAD FADHz + CHzCHCO-CoA 6) CHpCHCO-CoA+ HIO CHd0H)CH2CO-CoA (c) CHz(0H)CHCO-COA+ NADt NADH + H+ + CH(0)CH20-CoA (d) CH(O)CH20-CoA+ NADt NADH + H+ + -OZCCHzCO-CoA (e) -02CCHzCO-CoA Ht COI + CHZCO-CoA A mechanism should show the loss of COz and formation of a earbanion that is in resonance withan enolate ion. Acetyl-CoA is formed following acquisition of a hydrogen ion.
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2. (a) CHaCH(OH)CH(NH:)CO;
(b) CH&(O)CH(NH:)CO,
+ NAD+
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NADH + H+
+ CH&(O)CH(NHj)CO; + H+ % CH&(O)CHzNHj + C02
+ a-ketoelutarate % " glutamate + CH8C(0)CH0 (d) CH3C(O)CHO + NAD+ NADH + Ht + CHBC(0)CO; (c) . .
CH&(0)CHnNH! " . . " "
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logicnl enzyme hmnd intermediate for reaction id) ir E-SCHIOII)C(OICH,uith the sulfur provid~dhy a cyskinr rcsidor un che e n q me. The thiohrmincetnl intprmediate ia hydrolized to produce pyruvate; however, credit is given to students that couple a synthesis of ATP to this process by way of a reaction on the model of elvceraldehvde 3.ohasohorolvsis . phosphate iehydropmse. I\
3. (a) -0&CHzCHzCH(NH~)CO;%
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-02CCH(CH3)CH(NH~)C0, (b) -O2CCH(CH3)CH(NH:)C0; NH: + -02CC(CHXHC0; (c) -O2CC(CH~)CHC02 + HzO -OgCC(CHJ(OH)CHzCO; CH3C(0)CO; + CH3CO; (d) -O&C(CHd(OH)CH&O; The mechanism of reaction (d) probably involves a resonsncestabilized carbanion analogous to the reverse of an aldol condensation.
