F22 Exam Key

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University of Missouri, Columbia *

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4270

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Chemistry

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Jan 9, 2024

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Name ____________________________ Student Number _______________________ 1 Biochemistry 4270 / 7270 Exam 2 FS 2022 PLEASE KEEP EXAM CLOSED UNTIL GIVEN THE SIGNAL TO START EQUATIONS pH = log 1 D G’ 0 = -RT ln Keq [H + ] pH = -log [H+] D G = D G’ 0 + RT ln Q pH = pKa + log [A-] [HA] D G’ 0 = - n F D E’ 0 Keq = [H+] [A-] = K a [HA] pK a = log 1 = -log K a K a △ G = △ H – T △ S K a = [PL] = k a [P][L] k d K d = 1 K a Q = [c] [d] [a] [b] Y = [L] [L] + K d V 0 = V max [S] K m + [S] 1 = K m + 1 V 0 V max [S] V max Constants R = 8.315 J/K-mol R = 0.0821 L-atm/mol-K RT = 2.48 kJ/mol at 25°C RT = 2.58 kJ/mol at 37°C 1 kcal/mol = 4.184 kJ/mol K = 273 + ˚C Avogadro's number = 6.022 x 10 23 F= 96.5 kJ/V•mol

Name ____________________________ Student Number _______________________ 2 1) Answer the following questions about the reduction of FAD to FADH 2 in flavoproteins (8 points total) FAD + NADH + H + à FADH 2 + NAD + Use the half reactions below to answer the questions. FAD + 2H + + 2e - + à FADH 2 ΔE ́° = - 0.119 V NAD + + H + + 2e - + à NADH ΔE ́° = - 0.420 V a. Calculate ΔE ́° (in V) for the reduction of FAD by NADH (show work, 4 points). -0.119 – (-0.420) = +0.301 V 2point for work, 2 points for correct answer b. Calculate ΔG ́° (in kJ/mol) for the reduction of FAD by NADH (show work, 4 points). ∆ ࠵? ’ ࠵? = − ࠵?࠵? ∆ ࠵? ’ ࠵? = -(2) (96.480 kJ/mol-V) x (+0.301 V) = -58.1 kJ/mol 2 points for work, 2 points for correct answer 2) Choose the best answer – What is the importance of phosphorylated intermediates of glycolysis? (4 points) a. Trap intermediates within the mitochondria b. Phosphorylated compounds are low energy compounds that drive glycolysis forward c. Lots of energy is stored in O-P bond d. Binding energies of phosphate groups lowers activation energy and contribute to specificity of enzymes

Name ____________________________ Student Number _______________________ 3 3) Fill in the blank (9 points, 1 point each) Glycolytic enzyme with a Rossmann fold ______ G3P dehydrogenase ____ Glycolytic enzyme that catalyzes transfer of a phosphoryl group _ hexokinase ___ Energy harvesting reactions __ Catabolism ___ Energy consuming reactions __ anabolism ___ All the chemical processes occurring in an organism __ metabolism ___ Sugar with a 6-membered ring __ pyranose __ Structural polysaccharide composed of GlcNAc monomers ___ chitin ____ Structural polysaccharide composed of Glc monomers __ cellulose ___ Enzyme that converts fructose 1,6-bisphosphate to fructose 6-phosphate __ FBPase ___ Word Bank: Hexokinase Enolase Fructose 1,6-bisphosphatase Triose phosphate isomerase Glyceraldehyde 3-phosphate dehydrogenase Transferase Isomerase Catabolism Anabolism Metabolism Pyranose Furanose Ketose Aldose Chitin Cellulose Starch Glycogen 4) Below are electrophiles and nucleophiles. Circle the atom(s) in the structures below that serve as electrophiles or nucleophiles and label if that atom serves as a nucleophile or electrophile (4 points) 1 point for each correct answer C O R R P O - - O O OH S - nucleophile electrophile electrophile nucleophile

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Name ____________________________ Student Number _______________________ 4 5) Fill in the missing boxes based on these steps from glycolysis. Fill in the boxes with the missing substrates, products, cofactors, enzyme names, and reaction reversibility may be missing from the below reactions. For substrates and products draw structures. (arrow heads do not provide an indication of whether these reactions are reversible or irreversible) (9 points) 2 points each for correct structures, 1 point each for other blanks 6) In the presence of O 2 , what is the fate of pyruvate in humans? (2 points) a. Lactic acid fermentation b. Alcohol fermentation c. Cellular respiration d. Pentose phosphate pathway 7) Below is a D-monosaccharide in the black box and a few stereoisomers. Identify each of these compounds as an anomer, enantiomer, and/or epimer if applicable of the D- monosaccharide. (4 points) 2 points for correctly identifying epimer, 2 points for correctly identifying enantiomer NADH NAD+ Glyceraldehyde 3-phosphate Triose P isomerase G3P dehydrogenase Dihydroxyacetone phosphate C HC CH 2 OPO 3 2- OH O OPO 3 2- C HC CH 2 OPO 3 2- OH O H CH 2 OH C CH 2 OPO 3 2- O reversible reversible + 1,3-BPG P O - - O O OH C C O H C C H HO H HO H OH H HO CH 2 OH C C O H C C OH H OH H HO H OH H CH 2 OH C C O H C C H HO OH H HO H OH H CH 2 OH C C O H C OH H H HO H OH OH H CH 2 OH D-monosaccharide Epimer – 1 stereocenter different Enantiomer – all sterocenters inverted Not an epimer, anomer or enantiomer

Name ____________________________ Student Number _______________________ 5 8) Rank the relative oxidation states of the following compounds from most reduced (left) to most oxidized (right). (4 points) ___a__, ___c___, ___d__, ___b____ If correct order but listed from oxidized to reduced half points 9) In lactic acid fermentation, pyruvate is converted into lactate, this is an example of a/an ______________ reaction. (2 points) a) oxidoreductase b) transferase c) hydrolase d) lyase e) isomerase 10) D G’ ° of the following reaction is 7.3 kJ/mol, what value of Q would make this a spontaneous reaction? Show work (6 points) 3 points for work, 3 points for correct answer H 3 C C CH 3 O H 3 C H 2 C H 2 C OH H 3 C H 2 C C H O H 3 C H 2 C CH 3 (a) (b) (c) (d) Glucose 6-phosphate Glucose 1-phosphate D G’ ° = 7.3 kJ/mol

Name ____________________________ Student Number _______________________ 6 11) Label the semiquinone structure of FAD and the reduced form of NAD + /NADH. (4 points) FAD semiquinone – (C), reduced NADH – (D) 2 points each for correct identification 12) Provide an example of a covalent modification regulatory mechanism of glycolysis and gluconeogenesis. Name the modification, the enzyme it occurs on, and whether it activates or deactivates this enzyme. (3 points) Pyruvate kinase – phosphorylated, deactivated 13) When the energy status of the cell is high, which pathway is favored? (2 points) a. Glycolysis b. Gluconeogenesis c. Glycogen breakdown d. Metabolism 14) True or False. The irreversible reactions are shared between glycolysis and gluconeogenesis. (2 points) False N + NH 2 O R H N NH 2 O R H H N N N NH O O H 3 C H 3 C R N + H N N NH O - O H 3 C H 3 C R N H N N H NH O O H 3 C H 3 C R (a) (b) (c) (d) (e)

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Name ____________________________ Student Number _______________________ 7 15) Explain the mode of action by which insulin regulates glycolysis/gluconeogenesis. (3 points) Insulin release is triggered by high [Glu] in the blood (1 point) Insulin stimulates glycolysis through the allosteric regulator F26BP (1 point) Increases F26BP levels, which enhance PFK activity (1 point) 16) Below is the first step for the hexokinase reaction mechanism. Identify the catalytic residue, nucleophile and electrophile. Draw the reminder of the mechanism through the pentavalent intermediate to the products. Circle the pentavalent intermediate (10 points) 1 point each for catalytic residue, nucleophile and electrophile, 3 points for correct prodcuts (G6P, ADP, ASP deprotonated), 3 points for arrow pushing (1 each), 1 point for pentavalent intermediate ID.

Name ____________________________ Student Number _______________________ 8 nucleophile electrophile

Name ____________________________ Student Number _______________________ 9 17) Which statement is TRUE for the reciprocal regulation of phosphofructokinase (PFK) and fructose 1,6-bisphosphatase (FBPase)? (4 points) a. Fructose 1,6-bisphosphate inhibits PFK-1 and activates FBPase-1. b. Fructose 2,6-bisphosphate inhibits PFK-1 and activates FBPase-1. c. Fructose 1,6-bisphosphate inhibits FBPase-1 and activates PFK-1. d. Fructose 2,6-bisphosphate inhibits FBPase-1 and activates PFK-1. 18) Draw the Haworth perspective of the product of the phosphohexose isomerase reaction in the beta configuration. (5 points) 3 points for correct F6P, 2 points for beta conformation 19) In the first by-pass step of gluconeogenesis pyruvate carboxylase is localized in the mitochondria. Why is malate dehydrogenase also used in the first by-pass step? (4 points) The product, OAA is stuck in the mitochondria (1 point), because no mitochondria transporter of OAA (1 point). Thus, malate dehydrogenase converts OAA to malate (1 point), which can be exported to the cytosol for the rest of the by-pass steps (1 point). 20) There are three main differences between HK isoforms I-III and 1V, name two of these differences. (4 points) 1) Km HKI-III low Km, HKIV high Km. leads to HKI-III on/off whereas HKIV dimmer switch 2) HKI-III allosterically inhibited by F6P 3) HKIV regulated by a liver specific protein

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Name ____________________________ Student Number _______________________ 10 21) Ingested dietary glycogen and endogenous glycogen in the liver are processed by different feeder pathways to enter glycolysis. a) What is the first enzyme in the dietary glycogen feeder pathway? (2 points) Alpha-amylase b) What is the first enzyme in the endogenous glycogen feeder pathway? (2 points) phosphorylase 22) Circle the nonreducing end of the below disaccharide? (2 points) Anomeric carbon not involved in glycosidic linkage is the reducing end, the nonreducing end is the right side of this disaccharide O O CH 2 OH OH OH OH O CH 2 OH OH OH OH