Dr. Roger Miesfeld Bioc 460 Spring 20051Metabolic Integration1. What hormonal response explains why it is a bad idea to eat a candy bar with high sugarcontent prior to a bicycle race in which the cyclist's metabolic needs will be dependent on storedfats for energy? 2. Describe the major energy sources for the brain after 1, 3 and 40 days of fasting. Why is itadvantageous in mammals for the body to alter the preferred energy source of the brain awayfrom glucose after during prolonged starvation (i.e., what does it accomplish)?3. What does the Cori cycle accomplish during moderate exercise (jogging) that is critical tosustained activity?4. How can insulin treatment after a high glucose meal be used to distinguish between Type 1and Type 2 diabetes in a newly diagnosed patient?5. Of the three diets listed below, which would provide the most complete nutrition? Explain.1. carbohydrate + protein2. carbohydrate + fats3. protein + fats6. An extreme example of the Adkins diet consists of only fats and protein without anycarbohydrate. What explains the often encountered side effect of "acetone" breath on dietersusing this regimen?7. Which of the three meals listed below would be the most deficient in carbohydrates? Explain.a) pasta with parmesan cheeseb) rice and swordfishc) chicken cooked in sunflower oil8. What is the carbohydrate furnace referring to in the phrase “Fat is the fuel of the carbohydratefurnace?”9. What class of metabolites can be found at high concentrations in the blood of undiagnosedType I diabetics, and in people who have not eaten for 10 days?10. What is the biochemical explanation for the high level of ketone bodies in untreateddiabetics?11. Why do ketone bodies accumulate in the blood under starvation conditions?Dr. Roger Miesfeld Bioc 460 Spring 20052Answers1. Eating a candy bar will cause an sharp rise in insulin levels. Insulin signals the fed state(leading to the inhibition of fatty acid oxidation). Therefore the short rush of glucose at thebeginning of the race is detrimental later when fat utilization is needed. 2. The major energy source of the brain after 1 day is glucose from glycogen, after 3 days it isa mixture of glucose and ketone bodies, and after 40 days the brain draws the majority of itsenergy from ketone bodies. Shifting the brain's energy sources away from glucose towardketone bodies during prolonged starvation spares protein degradation as a source of carbonskeletons for gluconeogenesis. If all the muscle were catabolized to keep the brain supplied withglucose, the animal would not be able to respond quickly enough to available food sources thatinadvertently wander by.3. It ensures that lactate made by anaerobic glycolysis in the muscle is transported back to theliver where it is used as a precursor for gluconeogenesis to provide glucose for the muscle cells.4. Type 1 diabetes is characterized by lack of insulin production, whereas, Type 2 diabetes isdue to defects in the ability to respond to insulin. Therefore, if the patient's glucose levelsdropped after insulin injection, they most likely have Type 1 diabetes, if the glucose levels do notdrop, then they more likely have Type 2 diabetes.5. Diet #1 is the most complete because proteins are required (9 essential amino acids), andfats can be synthesized from carbohydrates, but carbohydrates cannot be synthesized from fats.6. In the absence of carbohydrate intake, OAA, a-ketoglutarate, and pyruvate are derived fromamino acid degradation. The acetone breath indicates that these reactions are not sufficient tokeep the Citric Acid Cycle functioning at full capacity and acetyl CoA builds up, leading to theproduction of ketone bodies.7. Meal (c) is the most deficient in carbohydrates as compared to the other two which containfoods rich in carbohydrates (pasta and rice).8. The “carbohydrate furnace” refers to the citrate cycle which is dependent on the balance ofpyruvate and oxaloacetate to provide sufficient substrate in the citrate synthase reaction duringtimes when acetyl CoA levels are high due to fatty acid oxidation.9. Ketone bodies (acetoacetate, acetone, and hydroxybutyrate) are present at highconcentrations in the blood as a result of diabetes and starvation.10. Diabetics have lost the ability to respond to high glucose levels in the blood due to theinability to produce or respond to insulin. Under these conditions, the body responds to adecreased level of glucose inside the liver by increasing fatty acid degradation. The excessacetyl CoA is converted to ketone bodies by enzymes in the liver.11. During starvation there is a high level of fatty acid oxidation producing large amounts ofacetyl CoA, however, insufficient levels of carbohydrates limit the availability of OAA due toinsufficient levels of pyruvate needed to produce OAA via the pyruvate carboxylase reaction.The excess acetyl CoA is converted to ketone bodies by enzymes in the
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