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Fall '04 Hackert/Kitto CH395G EXAM 3 Name _____________________ UT_ID _____________________ SHOW WORK FOR ALL COMPUTATIONAL PROBLEMS OR NO CREDIT! 1 cal = 4.184 J; R = 8.314 J/mole K = 1.99 cal/mole K; Avagadros number = 6 x 1023 Faraday’s constant = 23.1 Kcal/molV = 96.5 KJ/molV; Assume T=25 C in all problems, unless stated otherwise. 1. -keto acids are of considerable biochemical utility. Write the structural formulas for oxaloacetate, pyridoxal-5’-P, and -ketoglutarate. Identify the amino acids that arise from the two acids by simple transamination in the bottom of the appropriate box. (6) Oxaloacetate Pyridoxal-5’-Phosphate -Ketoglutarate AA __________ AA ___________ (4) In the schematic below of the citric acid cycle, fill in the boxes labeled “A”,”C”,”H” and “J”. (4) Which is the main regulatory step (number) step in the pathway? ______________________. This enzyme’s name is _____________________: It is inhibited by _____________________. Which numbered step(s) in the pathway is(are) effectively irreversible? __________________ 2. Triacylglycerols have the highest energy content of any of the major nutrients. (a) If 15% of the body mass of a 70 kg adult consists of triacylglycerols, calculate the total available fuel reserve, in both kilojoules and kilocalories, in the form of triacylglycerols. (2) (b) If the basal energy requirement is approximately 8,400 kJ/day (2,000 kcal/day), how long could this person survive if the oxidation of fatty acids stored as triacylglycerols were used as the only source of energy? (2) (c) What would be the corresponding weight loss in pounds per day under such starvation conditions (1 lb = 0.454 kg)? (2) (3) If an activated 17-carbon fatty acid goes through just -oxidation, what are the products? 17-C fatty acyl-CoA ___ acetyl-CoA + ___ FADH2 + ___ NADH + ___ _____________ (3) What is the general role of the ketone bodies? Name two of the ketone bodies. ____________________ ______________________ Name two conditions that can cause ketosis: ___________________________ ___________________________ 3. (4) In a mammalian electron transport system, electrons are donated from ________ to complex I; the enzyme that binds and oxidizes the cofactor is called ____________________ _________________. The electrons pass through complex I and reduce a lipid soluble mobile carrier called ____________________, which in turn carries ____(#) electrons to complex _______. Electrons then pass through this complex and reduce a soluble protein carrier called ________________; this reduction requires ____(#) electrons per molecule. The reduced carrier shuttles electrons to another complex where the electrons pass to the ultimate receptor, _________________. (4) Given that the redox potential for O2 is +0.82 V, and that of NAD+ is -0.32 V, how much energy, in KJ/mol, is released when 2 electrons from NADH are passed to atomic oxygen? Show work. (2) Cyanide and dinitrophenol are both inhibitors that decrease the production of ATP. Describe the differences in the effects of these inhibitors on mitochondrial function. (2) When the F1 portion of the ATP synthetase complex is removed from the mitochondrial membrane and studied in solution, does it function as an ATP synthetase? If not, why? 4. (2) Photosynthesis is arguably the most important metabolic pathway, since essentially all our food and fiber is made by the process. Photosynthetic “light reactions” harvest solar power and generate high energy chemicals like ATP and NADPH. Name two of the general types of photosynthetic pigments used to harvest light. _________________________ _________________________ (2) Why are so many pigments needed? (3) Sketch the “Z”-scheme of plant photosynthesis illustrating the flow of electrons and protons. Include in your sketch the following: Water / P700 / P680 / Ferredoxin / NADPH / Plastoquinone / Cyt b6f / and Plastocyanin. (4) In higher plants, photosynthesis moves electrons from the donor molecule __________________ to the acceptor molecule _________________. This process corresponds to a Gibbs Free Energy change of about +438 kJ/mol. Given the formula E = 1.2 x 105 (KJ/mol)/nm, estimate the minimum number of photons of green light ( = 560 nm) required, in theory, to supply the energy to move these four electrons? ________. (2) How many photons are used by nature to accomplish this process? ___________ (2) The compound that condenses with CO2 in the first reaction of carbon dioxide fixation is: ________________________________________________ 5. The amine groups from a wide range of amino acids are transferred to -ketoglutarate to form which amino acid? _________________ (4) This reaction involves the participation of which vitamin-derived cofactor? ______________ Name the two immediate precursors that furnish the nitrogens incorporated into urea. ________________________ & _____________________________ Name the three common materials synthesized for purposes of disposing of excess nitrogen. Give an example of an organism that uses each mechanism? 1) -(3) 2) -3) -- (2) Urea synthesis in mammals takes place primarily in the ________________ (organ). (4) Once amine groups are removed, the carbon skeletons of amino acids can be catabolized much like carbohydrates. The most common amino acid is alanine; if it is transaminated, what product remains? __________________. How much energy, in integral ATP units, can be gained by oxidizing this product all the way to carbon dioxide and water? ______________. (SHOW WORK and STATE ASSUMPTIONS) (3) Matching: ___ biotin ___ pyridoxal phosphate ___ UTP ___ THF ___ FAD ___ Acyl carrier protein a) methylene group transfers b) succinate dehydrogenase c) CO2 transfers d) fatty acid synthesis e) transaminations f) glycogen and sugar biosynthesis 6. Below are summaries of two clinical case studies: For each case select an enzyme from List A that is defective and designate the appropriate treatment from the List B. Then answer the question(s) raised in each case study. List A - Defective Enzymes (a) Muscle phosphofructokinase-1 (b) Phosphomannose isomerase (c) Galactose 1-phosphate uridylyltransferase (d) Liver glycogen phosphorylase (e) Triose kinase (f) Lactase of intestinal epithelial cells (g) Maltase of intestinal epithelial cells List B - Treatments 1. Frequent regular feedings 2. Fat-free diet 3. Low-lactose diet 4. Large doses of niacin (the precursor of NAD+ ) Case A – Defective Enzyme = _____________; Treatment = _______________ The patient develops vomiting and diarrhea shortly after milk ingestion. A lactose tolerance test is administered. The patient ingests a standard amount of lactose, and the glucose and galactose concentrations in blood plasma are measured at intervals. In lactose-tolerant individuals the levels increase to a maximum in about 1 h, then decline. Explain why. In this case the patient’s blood glucose and galactose levels do not increase during the test. Explain why. (4) Case B - Defective Enzyme = _____________; Treatment = _______________ The patient is lethargic and her liver is enlarged. A liver biopsy shows large amounts of excess glycogen. She also has lower than normal blood glucose. Why does this patient have low blood glucose? (4)