Mammalian Fuel Metabolism: Integration and Regulation

Mammalian Fuel Metabolism: Integration and Regulation

Matching

• Glucokinase Activity: Increases with high blood glucose. (Answer: G - Liver)
• Kidney Function: Excretes urea and other waste products from the blood. (Answer: K - Urea)
• Cori Cycle: Provides a pathway for the metabolic use of lactate for glucose production. (Answer: C - Cori cycle)
• Endocrine Glands: Secrete hormones that result in numerous cellular responses. (Answer: H - Hormones)
• Epinephrine Binding: Binding to the α-adrenergic receptor causes an increase in intracellular [Ca^{2+}]. (Answer: A - α-adrenergic receptor)
• Prolonged Starvation: Ketone bodies are used as fuel by the brain. (Answer: J - Ketone bodies)
• Acetyl CoA: The degradation product of glucose, fatty acids, and ketogenic amino acids. (Answer: I - Acetyl CoA)
• Starvation & Glucose: During starvation, the kidney generates as much as 50% of the body's glucose supply. (Answer: L - Kidney)
• Brain's Energy Needs: The brain stores very little glycogen and therefore requires a steady supply of glucose from the blood. (Answer: M - Brain)
• Leptin Deficiency: Mice lacking the protein leptin are genetically obese. (Answer: E - Leptin)

Multiple Choice

• Preferred Muscle Fuel: Glucose is the preferred fuel of muscles because it can be metabolized under anaerobic conditions. (Answer: A)
• Muscle Glucose Transporter: The glucose transporter in muscle cells is GLUT4. (Answer: D)
• Adenylate Cyclase Reaction: Adenylate cyclase catalyzes the reaction ATP → cAMP + PPi. (Answer: A)
• Phospholipase C Cleavage: Phospholipase C cleaves PIP2, generating IP3 and DAG (inositol-1,4,5-trisphosphate and 1,2-diacylglycerol). (Answer: A)
• Balanced Meal Digestion:
  • Fatty acids are absorbed by the intestinal mucosa and circulated through the lymph.
  • Proteins are digested into monomer amino acids and absorbed by the intestinal mucosa, after which the majority is delivered to the liver. (Answer: C)
• Glucose Production Limitation: Animals lack the ability to produce glucose from fatty acids. (Answer: B)
• Common Products of Fuel Metabolism: The common products of fuel metabolism in mammals are pyruvate and acetyl-CoA. (Answer: B)
• ATP Regeneration Mechanisms: ATP regeneration mechanisms are utilized in the following order: phosphocreatine, glycolysis, oxidative phosphorylation. (Answer: B)
• Glucokinase Regulation: Glucokinase is regulated by glucokinase regulatory protein and fructose-6-phosphate. (Answer: A)
• Metabolic Fate of Glucose-6-Phosphate: The metabolic fates of glucose-6-phosphate include glycogen, glucose, ribose-5-phosphate, and acetyl-CoA. (Answer: E)
• Hepatocyte Response to Insulin (FALSE): Glucose uptake is increased in the liver (it's not directly stimulated by insulin). (Answer: D)
• Pancreatic β Cells: Insulin is secreted by the β cells in response to high glucose levels. (Answer: C)
• Effects of Insulin Secretion:
  • Muscle and adipose tissue are stimulated to take up glucose.
  • Glycogen synthesis increases in the liver.
  • Gluconeogenesis is inhibited in the liver and kidney. (Answer: C)
• Appetite Stimulating Protein: Ghrelin stimulates the appetite. (Answer: B)
• Leptin (FALSE): Obesity in humans leads to a decrease in leptin production (actually, obesity leads to increased leptin production and then resistance). (Answer: C)
• Blood Glucose in Non-Insulin Dependent Diabetics: Blood glucose levels of diabetics tend to be variable and higher than normal individuals. (Answer: B)
• Insulin-Dependent (Type 1) Diabetes: Is associated with a deficiency of pancreatic β-cells. (Answer: A)
• Aerobic Activity Under Stress: Glycolysis occurs in the muscle; glycogenolysis occurs in the muscle and liver. (Answer: A)
• Interorgan Nitrogen Transport: The interorgan pathway that allows transport of nitrogen from muscle to the liver utilizes pyruvate as an amino group acceptor in the transamination reaction generating alanine. (Answer: E)
• AMPK Function: AMP-dependent protein kinase (AMPK) activates ATP-generating metabolic pathways and inhibits biosynthetic pathways. (Answer: A)
• Liver Glucose Production at Low Concentrations: At low glucose concentrations (≤5mM), the majority of glucose produced by liver cells is due to the action of glucose-6-phosphatase. (Answer: C)
• Liver Glycogen Depletion: In an average individual, liver glycogen is depleted during starvation in approximately 18-24 hours. (Answer: C)
• Excess Glucosylation in Diabetics: Excess glucosylation of lens proteins in diabetics leads to cataracts. (Answer: A)
• Glucokinase Activity Curve: The curve labeled C corresponds to activity of glucokinase under conditions with no inhibition. The binding of F6P to the regulating protein would result in kinetic behavior represented by curve B.
• Brain Glucose Usage: The majority of glucose in the brain is used to produce ATP for membrane Na^+-K^+ ATPase required for nerve impulse transmission. (Answer: B)
• Triacylglycerol Synthesis Dependence: Synthesis of triacylglycerols is dependent on the availability of glycerol-3-phosphate, the uptake of glucose from the bloodstream, the enzyme responsible for reduction of dihydroxyacetone phosphate, and the circulation of lipoprotein. (Answer: E)
• Adipose Tissue:Secretes hormones that regulate metabolism. (Answer: A)
• Generates Glucose: Kidney and liver generates glucose. (Answer: C)
• Occurs During Starvation: During starvation the brain utilizes ketone bodies as a fuel source; the adipose tissue releases fatty acids and gluconeogenesis occurs in the liver. (Answer: B)
• Metabolizes Ketone Bodies: Brain and muscle metabolizes ketone bodies. (Answer: C)
• Muscle Metabolism Hormonal Control: Muscle metabolism is controlled hormonally by insulin and epinephrine. (Answer: D)
• Regulation of Metabolism: Metabolism is regulated by receptor tyrosine kinase, adenylate cyclase and phosphoinositide pathway. (Answer: D)
• Muscle and Liver interaction: None of the options are correct. (Answer: E)
• Glucose Update: Glucose update in the muscle is increased in response to insulin due to increased expression of GLUT4. (Answer: B)
• Activation of AMPK activity: Accomplished by AMP induced conformational changes facilitating phosphorylation. (Answer: A)
• Lifespan Extension in Rodents: Evidence suggests that the lifespan of a rodent may be extended 50% by a 30-40% reduction in calorie intake. (Answer: B)
• Type 2 Diabetes: Can develop due to a mutation in the insulin receptor and can develop in individuals with insulin resistance. (Answer: B)
• Stored Caloric Energy During Prolonged Starvation: During prolonged starvation the majority of the stored caloric energy comes from fat stores. Muscle protein provides the second largest caloric energy total. (Answer: D)
• Metabolic Syndrome Characteristics: Insulin resistance and infammation are characteristics of metabolic syndrome. (Answer: A)
• Metformin and Thiazolidinediones (TZDs): Are used to treat type 2 diabetes and produce a(an) increase in AMPK activity. (Answer: B)