20090527 DEPARTMENT OF BIOCHEMISTRY / TIME / TYD: 90 MIN DEPARTEMENT BIOCHEMIE BCM 255 MARKS / PUNTE: 85 EXAM / EKSAMEN EXTERNAL EXAMINER: / EKSTERNE EKSAMINATOR: INTERNAL EXAMINER: / INTERNE EKSAMINATOR: PROF AWH NEITZ DR ARM GASPAR QUESTION / VRAAG 1: [24] Refer to the figure below to answer the questions that follow: / Verwys na die figuur onder om die volgende vrae te beantwoord: 1 of 12 Pages
1.1 Identify and draw the Haworth structures for two of the three sugar substrates (excluding glucose) of the enzyme hexokinase. / Identifiseer en teken die Haworthstrukture vir twee van die drie suikersubstrate (uitsluitend glukose) van die heksokinase ensiem. (3) 1.2 Identify the enzyme catalyzing the reaction at the second control point of glycolysis. / Identifiseer die ensiem wat die reaksie kataliseer by die tweede kontrolepunt van glikolise. (1)... 1.3 The enzyme referred to in 1.2 is activated by high levels of a metabolite produced from fructose-6-phosphate. Show with appropriate reactions (complete, with structures) how this metabolite is formed and broken down, respectively. / Die ensiem verwys na in 1.2 word ge-aktiveer deur hoë vlakke van n metaboliet wat gevorm word vanuit fructose-6-fosfaat. Toon aan mbv toepaslike reaksies (volledig, met strukture) hoe hierdie metaboliet gevorm en afgebreek word, onderskeidelik. (6½) 2 of 12 Pages
1.4 The only redox reaction of glycolysis is indicated in the above figure. Give the reverse reaction (complete, with structures) for this step during gluconeogenesis. / Die enigste redoksreaksie in glikolise is aangedui in die bogenoemde figuur. Gee die omgekeerde reaksie (volledig, met strukture) vir hierdie stap tydens glukoneogenese. (4½) 1.5 Which glycolytic intermediate (name only) will glycerol be converted into in order for glycerol to be used for the synthesis of glucose? / Na watter glikolitiese tussenproduk (slegs naam) moet gliserol omgeskakel word sodat gliserol gebruik kan word vir die sintese van glukose? (½)... 1.6 Explain by means of a fully annotated diagram (with structures where applicable) how NADH produced during glycolysis is transported to the mitochondrial matrix by the glycerol-phosphate shuttle mechanism. / Verduidelik mbv n volledige ge-annoteerde diagram hoe NADH geproduseer tydens glikolise dmv die gliserolfosfaat pendelmeganisme na die mitochondriale matriks vervoer word. (8½) 3 of 12 Pages
QUESTION / VRAAG 2: [15] 2.1 The following reactions occur in the oxidative phase of the pentose phosphate pathway: / Die volgende reaksies vind plaas in die oksidatiewe fase van die pentosefosfaatpadweg: / Glucose 6 phosphate / Glukose 6 fosfaat Ribulose 5 phosphate / Ribulose 5 fosfaat 1. 3. 6 Phosphoglucono lactone / 6 Fosfoglukono laktoon 2. 6 Phosphogluconate / 6 Fosfoglukonaat 2.1.1 Identify each type of reaction for steps 1-3. / Identifiseer elke tipe reaksie vir stappe 1-3. (1½) 1:... 2:... 3:... 2.1.2 Give the names of the enzymes that catalyze the following steps. / Gee die name vir die ensieme wat die volgende stappe kataliseer. (3) 1:... 2:... 3:... 2.1.3 Draw the structure for 6-phosphogluconate and indicate on the structure the functional group that is released as well the functional group that is modified during reaction 3. / Teken die struktuur vir 6-fosfoglukonaat en dui op die struktuur aan watter funksionele groep vrygestel word asook watter funksionele groep gemodifiseer word tydens reaksie 3. (2) 4 of 12 Pages
2.1.4 Draw the structures for the products formed by the action of phosphopentose isomerase and phosphopentose-3-epimerase on ribulose-5-phosphate, respectively. / Teken die strukture vir die produkte wat vorm deur die aksie van fosfopentoseisomerase en fosfopentose-3-epimerase op ribulose-5- fosfaat, onderskeidelik. (2) ribulose-5-phosphate/-fosfaat ribulose-5-phosphate/-fosfaat 2.2 Name or give. / Noem of gee. 2.2.1 The enantiomer of L-sedoheptulose. / Die enantiomeer van L-sedoheptulose. (½) 2.2.2 The number of phosphoanhydride bonds in ATP. / Die aantal fosfo-anhidriedbindings in ATP. (½) 2.2.3 The biochemical reason why muscle glycogen cannot be utilized to supplement the blood with glucose. / Die biochemiese rede waarom spierglikogeen nie gebruik kan word om bloedglukose-vlakke aan te vul nie. (1½) 5 of 12 Pages
2.2.4 The pentose phosphate pathway enzymes that will be affected by a shortage of thiamine in the diet. / Die pentosefosfaatpadweg ensieme wat beïnvloed sal word deur n tekort aan tiamien in die dieet. (1) 2.2.5 The activated form of glucose (give structure) that is used as a substrate by glycogen synthase. / Die geaktiveerde vorm van glukose (gee struktuur) wat gebruik word as substraat deur glikogeensintase. (1) 2.2.6 The type of glycosidic bonds in glycogen. / Die tipe glikosidiese bindings in glikogeen. (1) 2.2.7 The enzyme that releases glucose-1-phosphate from the non-reducing ends of glycogen. / Die ensieme wat glukose-1-fosfaat vrystel vanaf die nie-reduserende ente van glikogeen. (1) QUESTION / VRAAG 3: [24] 3.1 The pyruvate dehydrogenase complex catalyzes the conversion of pyruvate to acetyl-coa. / Die piruvaatdehidrogenasekompleks kataliseer die omskakeling van piruvaat na asetiel-koa. 3.1.1 Draw the structures for pyruvate and acetyl-coa. / Teken die strukture vir piruvaat en asetiel-koa. (2) 6 of 12 Pages
3.1.2 List the coenzymes (as well as the vitamin precursor for each) required for the action of the enzyme complex. / Lys die koënsieme (asook elk se vitamien voorganger) wat benodig word vir die werking van die ensiemkompleks. (4½) 3.1.3 Pyruvate is used for the anabolism of an amino acid. Which one? / Piruvaat word gebruik vir die anabolisme van n aminosuur. Watter een? (1) 3.1.4 Which reaction (give only name and structure for the main substrate) in the Krebs cycle is similar to the reaction catalyzed by the pyruvate dehydrogenase complex? / Watter reaksie in die Krebs-siklus (gee slegs naam en struktuur vir die hoof substraat) is soortgelyk aan die reaksie gekataliseer deur die piruvaatdehidrogenasekompleks? (1½) 3.2 The following is reaction 5 of the Krebs cycle: / Die volgende is reakie 5 van die Krebs-siklus: 3. 4. 1. 2. 5. 7 of 12 Pages
3.2.1 Indicate the thioester bond on the above structure. / Dui die tioesterbinding op die bogenoemde struktuur aan. (½) 3.2.2 Provide the relevant information 1-5 in the space below (give structures where applicable). / Verskaf die relevante inligting 1-5 in die spasie hieronder (gee strukture waar van toepassing). (3½) 1. 4. 2. 3. 5. 3.2.3 Show clearly how you would calculate the G 0 ' for the above reaction if the G 0 ' values for the hydrolysis of the substrate and GTP are 8.0 and 7.3 kcal/mol, respectively. / Dui duidelik aan hoe jy die G 0 ' vir die bogenoemde reaksie sou bereken indien die G 0 '-waardes vir die hidrolise van die substraat en GTP, 8.0 en 7.3 kkal/mol is, onderskeidelik. (2½) 3.3 The following are reactions 7 and 8 of the Krebs-cycle. / Die volgende is reaksies 7 en 8 van die Krebs-siklus. Fumarate / Fumaraat 7 L-Malate / 8 L-Malaat Oxaloacetate (OAA) / Oksaloasetaat (OAA) 8 of 12 Pages
3.3.1 Draw the structures for fumarate and L-malate. / Teken die strukture vir fumaraat en L-malaat. (2) 3.3.2 Give the names for the enzymes for reactions 7 and 8, respectively. / Gee die name vir die ensieme vir reaksies 7 en 8, onderskeidelik. (2) 7:... 8:... 3.3.3 Which other product is formed at reaction 8? / Watter ander produk vorm by reaksie 8? (½) 3.3.4 Give the reaction (complete, without structures) that replenishes the level of OAA when the level of this metabolite drops. / Gee die reaksie, (volledig, sonder strukture) wat OAA vlakke aanvul wanneer die vlak van die metaboliet daal. (4) QUESTION / VRAAG 4: [22] 4.1 Complete the reaction below (give names and structures for the products) for one of the unique reactions of the glyoxylate cycle. / Voltooi die reaksie onder (gee name en strukture vir die produkte) vir een van die unieke reaksies van die glioksilaatsiklus. (3) 9 of 12 Pages
4.2 Consider the following schematic representation of oxidative phosphorylation and answer the questions that follow: / Beskou die volgende skematiese voorstelling van oksidatiewe fosforilasie en beantwoord die vrae wat volg: a b I II CoQ III Cytc IV V c 1 2 3 4 5 6 7 8 9 4.2.1 Give names for complexes II, IV and V. / Gee name vir komplekse II, IV en V. (3) II:... IV:... V:... 4.2.2 Identify mitochondrion compartments a, b and c. / Identifiseer mitochondrion kompartemente a, b en c. (1½) a:... b:... c:... 10 of 12 Pages
4.2.3 Identify substrates and products 1-9. / Identifiseer substrate en produkte 1-9. (4½) 1:... 2:... 3:... 4:... 5:... 6:... 7:... 8:... 9:... 4.2.4 Which component is not bound to any protein? / Watter komponent is nie gebind aan enige proteïen nie? (½)... 4.2.5 Which complexes (give numbers) are inhibited by rotenone and CO, respectively? / Watter komplekse (gee nommers) word geïnhibeer deur rotenoon en CO, onderskeidelik? (1) 4.2.6 Indicate on the above scheme the flow of protons during phosphorylation. / Dui aan op bogenoemde skema die vloei van protone tydens fosforilasie. (½) 4.2.7 Consider the following half reactions: / Beskou die volgende halfreaksies: FAD + 2H + + 2e - FADH 2 ½ O 2 + 2H + + 2e - H 2 O E o = 0.091 V E o = 0.816 V Calculate both E o and G 0 for the net reaction of the electron transport system. [F = 23.062 (kcal/v)] Bereken beide E o en G 0 vir die netto reaksie van die elektronvervoersisteem. [F = 23.062 kkal/ V]. (4) 11 of 12 Pages
4.3 Compare the Krebs cycle with the Calvin cycle by giving the structures (and names) for the acceptor molecules for each respective cycle. Which molecules enter the respective cycles? / Vergelyk die Krebs-siklus met die Calvin-siklus deur die strukture (en name) vir die ontvanger molekule vir elke siklus te gee. Watter molekule word deur elk van die onderskeie ontvanger molekuul ontvang? (4) Calvin cycle/ -siklus Krebs cycle/ -siklus Name of acceptor molecule / Naam van ontvanger molekuul Structure of acceptor molecule / Struktuur van ontvanger molekuul - Unit entering cycle / Eenhede wat by siklus aansluit ********** 12 of 12 Pages