Chapter 12: Bioenergetics and Regulation of Metabolism

Definition of free energy change (\Delta G) under nonstandard conditions

\Delta G = \Delta G^\circ + RT \ln(Q), where R is the gas constant, T is temperature, and Q is the reaction quotient.

Standard free energy change adjusted for physiological pH (\Delta G^{\circ\prime})

The free energy change at standard conditions except [H^+] = 10^{-7} M (pH 7) instead of 1 M (pH 0).

Reason ATP is an efficient energy carrier despite being thermodynamically unstable

ATP hydrolysis is exergonic due to charge repulsion between negative phosphate groups and resonance stabilization of free inorganic phosphate (P_i).

ATP cleavage (hydrolysis coupling) mechanism

The transfer of a phosphate group from ATP to another molecule to activate or energize an endergonic reaction.

Primary soluble electron carriers in catabolism

NADH, FADH_2, NADPH, ubiquinone (CoQ), cytochrome c, and glutathione.

Number of electrons carried by one molecule of NADH

2 electrons (transferred as a hydride ion, H^-).

Flavoproteins function and examples

Nucleic acid derivatives containing riboflavin (FAD or FMN) that act as electron acceptors in the ETC, fatty acid oxidation, and decarboxylation of pyruvate.

Postprandial (absorptive / well-fed) state hormonal profile

High insulin level, low glucagon level; marked by predominant anabolism (glycogen synthesis, fatty acid synthesis, protein synthesis).

Postabsorptive (fasting) state primary metabolic processes

Glycogenolysis in liver (immediate response), followed by hepatic gluconeogenesis; catabolism driven by elevated glucagon and catecholamines.

Prolonged fasting (starvation) fuel shift in the brain

The brain transitions from using glucose exclusively to deriving ~\frac{2}{3} of its energy from ketone bodies.

Metabolic effect of insulin on carbohydrates

Increases glucose uptake in muscle and adipose tissue, increases glycogen synthesis (glycogenesis) in liver and muscle, and promotes glycolysis.

Metabolic effect of glucagon on liver metabolism

Increases glycogenolysis, gluconeogenesis, lipolysis, and ketogenesis; decreases liver glycolysis.

Cortisol metabolic effects

Glucocorticoid that elevates blood glucose by mobilizing amino acids for gluconeogenesis, inhibiting glucose uptake in tissues, and enhancing glucagon/catecholamine activity.

Epinephrine metabolic effects on muscle and adipose tissue

Promotes glycogenolysis in muscle and stimulates hormone-sensitive lipase (HSL) in adipose tissue to release fatty acids.

Thyroid hormones (T_3 and T_4) mechanism in metabolic rate regulation

Increase basal metabolic rate by upregulating gene expression of metabolic enzymes; T_3 is rapid/short-acting, while T_4 is latent/long-acting.

Primary fuel source for liver in the postabsorptive (fasting) state

Fatty acids via \beta-oxidation.

Primary fuel source for resting skeletal muscle in the well-fed state vs fasting state

Well-fed: Glucose; Fasting: Free fatty acids.

Primary fuel source for active skeletal muscle during short, high-intensity exercise

Creatine phosphate and stored muscle glycogen (via anaerobic glycolysis).

Primary fuel source for cardiac muscle across all metabolic states

Fatty acids (can also utilize ketone bodies during starvation).

Primary fuel source for red blood cells (erythrocytes) under all conditions

Glucose exclusively, metabolized via anaerobic glycolysis (yielding 2 ATP per glucose).

Respiratory Quotient (RQ) formula

RQ = \frac{CO_2 \text{ produced}}{O_2 \text{ consumed}}

Expected Respiratory Quotient (RQ) value for pure carbohydrate oxidation vs pure lipid oxidation

Carbohydrates: RQ = 1.0; Lipids: RQ = 0.7 (Proteins \approx 0.8).

Role of ghrelin vs leptin vs orexin in appetite control

Ghrelin & Orexin: Stimulate appetite/hunger; Leptin: Suppresses appetite by acting on the hypothalamus.

Body Mass Index (BMI) calculation formula

BMI = \frac{\text{mass in kg}}{(\text{height in meters})^2}

Main metabolic tissue type responsible for maintaining blood glucose levels during fasting

The liver (via glycogenolysis and gluconeogenesis).