Bioenergetics and Regulation of Metabolism - Practice Problems

Problem 1: Adding heat to a closed biological system

• Answer: (C) Cause the system to do work to maintain a fixed internal energy
• Enthalpy, heat, and internal energy are directly related (no change in pressure or volume).
• Adding heat will:
  • Increase internal energy, vibrational, rotational, and translational energies, and enthalpy
  • Not cause the system to do work (due to fixed pressure and volume).

Problem 2: Delta G at different concentrations

• Answer: (B) Delta G is less than Delta G naught and the reaction is spontaneous
• Use equation: ΔG = ΔG⁰ + RT ln(Q)
• Q = (product concentrations) / (reactant concentrations)
• Given ΔG⁰ = 0, R = universal gas constant, T = 25°C, concentrations = 10 millimolar
• Calculation results in ΔG = -4RT
• Negative ΔG indicates a spontaneous process.

Problem 3: Hydrolysis of ATP

• Answer: (C) The free energy of hydrolysis of ATP is nearly the same for ADP
• Hydrolysis is energetically favorable due to repulsive negative charges being relieved and resonance stabilization.
• False statements:
  • Free energy of ATP hydrolysis is dependent on pH.
  • One mole of creatine phosphate phosphorylates one mole of ADP.
  • Hydrolysis yields AMP, not cyclic AMP.

Problem 4: Reduction half-reaction in the last step of the electron transport chain

• Answer: (A) Reduction is a gain of electrons forming H2O
• Reduction involves gaining electrons; oxygen is the final electron acceptor, forming H2O.

Problem 5: Electron carriers in oxidized/reduced states

• Answer: (B) Electron carriers
• Electron carriers (e.g., flavoproteins) transport electrons and must stabilize in both oxidized and reduced states.

Problem 6: Energy state in the introduction of the chapter

• Answer: (B) Post-absorptive (fasting) state
• Describes a scenario after absorption where body needs energy but no new food intake, thus shifting to gluconeogenesis and glycogenolysis.

Problem 7: Alternative fuel for the brain in prolonged fasting

• Answer: Ketone bodies
• Brain uses ketone bodies when glucose is scarce during prolonged fasting.

Problem 8: Hormonal vs. Allosteric control of glycogen metabolism

• Answer: (A) Hormonal control is systematic and covalent
• Hormonal controls (via insulin and glucagon) are systematic and affect the whole organism, typically through phosphorylation or dephosphorylation.
• Allosteric controls are local or systemic.

Problem 9: Tissue most dependent on insulin

• Answer: (B) Resting skeletal muscle and adipose tissue
• Require insulin for glucose uptake; active skeletal muscle does not.

Problem 10: Glucocorticoids and stress-related weight gain

• Answer: (C) Increase glucose levels causing insulin secretion
• Released glucose not used for metabolism promotes fat storage in adipose tissue under insulin stimulation.

Problem 11: Tissue most rapidly damaged in absence of oxygen

• Answer: Brain
• Brain relies exclusively on aerobic metabolism of glucose and is highly sensitive to oxygen deprivation.

Problem 12: Respiratory quotient of 0.7

• Answer: (B) Lipid metabolism
• RQ of 0.7 indicates primary metabolism of lipids.
• Other indicators: RQ 0.8-0.9 (amino acids), RQ 1 (carbohydrates).

Problem 13: Expected side effect of taking leptin

• Answer: (A) Drowsiness
• Leptin decreases appetite by inhibiting orexin, leading to reduced alertness and drowsiness.

Problem 14: False statement

• Answer: (C) ATP stores are turned over more than 10,000 times daily
• True turnover is about 1,000 times daily.
• True statements:
  • Growth hormone participates in glucose counter-regulation.
  • T4 acts more slowly than T3.
  • Catecholamines stimulate the sympathetic nervous system.

Problem 15: Process starting earliest in prolonged fast

• Answer: (D) Enzyme phosphorylation and dephosphorylation by glucagon
• Glucagon initiates phosphorylation of metabolic enzymes early in fasting.
• Subsequent processes: cessation of glycogen storage, protein breakdown, formation of ketone bodies.