Chapter 6: Energy Transfer in the Body

Comprehensive vocabulary flashcards covering the biochemical principles of energy transfer, ATP and PCr dynamics, glycolysis, oxidative phosphorylation, lipid catabolism, protein metabolism, and metabolic interconversions from Chapter 6.

Adenosine Triphosphate (ATP)

The energy-rich nucleotide compound that serves as the body's primary energy currency, harvesting energy from macronutrient oxidation to power all cellular and biological work.

Adenosine Triphosphatase (ATPase)

The enzyme that catalyzes the cleavage of ATP with water into adenosine diphosphate (ADP) and inorganic phosphate ($\text{P}_{\text{i}}$), releasing approximately $7.3\,\text{kcal}\cdot\text{mol}^{-1}$ of free energy ($-\Delta G$).

Phosphocreatine (PCr)

A high-energy phosphate compound stored in muscle cells at concentrations $4$ to $6$ times greater than ATP that anaerobically donates a phosphate to resynthesize ATP, reaching its maximum energy yield in about $10\,\text{s}$.

Creatine Phosphokinase

The enzyme that controls the reversible anaerobic reaction transferring a high-energy phosphate group between phosphocreatine (PCr) and ADP to regenerate ATP.

Electron Transport Chain

The final common aerobic pathway located in the mitochondrion where electrons removed from hydrogen atoms pass along cytochromes to molecular oxygen, forming water.

Oxidative Phosphorylation

The mitochondrial process that synthesizes ATP by transferring electrons from $\text{NADH}$ and $\text{FADH}_2$ to oxygen, accounting for approximately $90\%$ of all cellular ATP synthesis with an energy efficiency of $34\%$.

Chemiosmotic Coupling

The mechanism whereby electron transport reactions pump protons ($\text{H}^+$) across the inner mitochondrial membrane into the intermembrane space, creating an electrochemical gradient used to drive ATP synthesis.

Three Stages of Macronutrient Energy Release

The stepwise cellular sequence where Stage 1 digests, absorbs, and assimilates food macromolecules into smaller subunits; Stage 2 degrades subunits into acetyl-CoA; and Stage 3 oxidizes acetyl-CoA to $\text{CO}_2$ and $\text{H}_2\text{O}$ to produce large amounts of ATP.

Substrate-Level Phosphorylation

The direct transfer of energy and a phosphate group from an intermediate substrate molecule to ADP to form ATP during glycolysis and the citric acid cycle, operating at approximately $30\%$ efficiency.

Anaerobic (Rapid) Glycolysis

The oxygen-independent cytosolic breakdown of glucose into lactate, yielding a net of $2\,\text{ATP}$ ($14.6\,\text{kcal}\cdot\text{mol}^{-1}$) and releasing approximately $5\%$ of the total energy within the glucose molecule.

Aerobic (Slow) Glycolysis

The breakdown of glucose into pyruvate that subsequently converts to acetyl-CoA and enters the citric acid cycle and electron transport chain for complete aerobic catabolism.

Lactate

The acid salt formed during intense exercise when hydrogen production exceeds oxidation capacity; pyruvate temporarily binds hydrogen to form lactic acid, which dissociates a hydrogen ion ($\text{H}^+$) and binds to $\text{Na}^+$ or $\text{K}^+$.

Phosphofructokinase (PFK)

A key regulatory glycolytic enzyme that controls the conversion of fructose-6-phosphate to fructose 1,6-disphosphate, modulated by cellular energy status and inhibited by high oxygen concentrations.

Pyruvate Dehydrogenase

The mitochondrial multi-enzyme complex that converts pyruvate, $\text{NAD}^+$, and coenzyme A (CoA) into acetyl-CoA, $\text{CO}_2$, and $\text{NADH} + \text{H}^+$.

Citric Acid Cycle (Krebs Cycle)

The cyclic mitochondrial pathway that degrades acetyl-CoA into $\text{CO}_2$ and hydrogen atoms, producing $20$ hydrogen atoms, $6\,\text{CO}_2$, and $2\,\text{ATP}$ from two entering pyruvate molecules.

Net ATP Yield from Skeletal Muscle Glucose Oxidation

The complete aerobic breakdown of one glucose molecule yielding a net of $32\,\text{ATP}$ ($4\,\text{ATP}$ from substrate-level phosphorylation and $28\,\text{ATP}$ via oxidative phosphorylation, minus $2\,\text{ATP}$ initially consumed).

Hormone-Sensitive Lipase (HSL)

The enzyme within adipocytes and muscle tissue that stimulates the lipolytic breakdown of triacylglycerols into glycerol and three free fatty acids, activated by epinephrine, norepinephrine, glucagon, and growth hormone.

Albumin

The plasma carrier protein that binds and transports mobilized, hydrophobic free fatty acids (FFAs) through the bloodstream to active muscle tissue.

$\beta$-Oxidation (Beta-Oxidation)

The cyclic catabolic pathway inside the mitochondrion that sequentially cleaves two-carbon acyl groups from fatty acids to yield acetyl-CoA, generating $\text{NADH}$ and $\text{FADH}_2$ for the respiratory chain.

Triacylglycerol ATP Yield

The total energy production of $460\,\text{ATP}$ molecules generated from completely oxidizing one neutral fat molecule ($19\,\text{ATP}$ from glycerol catabolism and $441\,\text{ATP}$ from three 18-carbon fatty acids).

Metabolic Mill

The concept describing the citric acid cycle as a vital central metabolic hub that links carbohydrate, lipid, and protein metabolism and shuttles shared intermediates across cellular compartments.

Glucogenic Amino Acids

Amino acids whose carbon skeletons yield metabolic intermediates capable of synthesizing glucose via gluconeogenesis after nitrogen removal.

Ketogenic Amino Acids

Amino acids that, when deaminated, yield the intermediates acetyl-CoA or acetoacetate, used either for triacylglycerol synthesis or catabolized directly in the citric acid cycle.

Deamination

The biochemical removal of an amine group ($\text{NH}_2$) from an amino acid in the liver, producing ammonia ($\text{NH}_3$) which is converted to urea, leaving a carbon skeleton to enter aerobic energy pathways.

"Fats Burn in a Carbohydrate Flame"

The metabolic principle describing how continuous lipid catabolism through the citric acid cycle requires oxaloacetate and related intermediates continually supplied by carbohydrate breakdown.

Cellular ADP Concentration

The intracellular physiological indicator that exerts the single greatest stimulatory control over rate-limiting enzymes of energy metabolism to drive cellular ATP resynthesis.