Energy Metabolism Flashcards

Vocabulary flashcards covering cellular respiration, energy-yielding nutrients, metabolic pathways, energy balance, and expenditure components from the Energy Metabolism lecture.

Calorie

A unit of energy or heat, originally defined as the amount of heat required at a pressure of $1\text{ standard atmosphere}$ to raise the temperature of $1\text{ gram}$ of water by $1^\circ\text{C}$; it measures how much energy food gives off when burnt.

Anabolism

Metabolic reactions in which small molecules are assembled into larger ones, requiring energy (such as synthesizing glycogen from glucose, triglycerides from glycerol and fatty acids, or proteins from amino acids).

Catabolism

Metabolic reactions in which large molecules are broken down into smaller ones, releasing energy that is largely captured within the bonds of adenosine triphosphate (ATP).

Adenosine Triphosphate (ATP)

A high-energy compound composed of adenosine and three phosphate groups linked by high-energy bonds; when these bonds break, energy is released to power the body's cellular work.

Cytosol

A protein-rich jelly-like fluid that fills the spaces within the cytoplasm lattice and contains the enzymes involved in glycolysis (glucose breakdown).

Mitochondria

Known as the "powerhouses" of the cell; intricately folded membranous organelles housing enzymes for pyruvate-to-acetyl CoA conversion, fatty acid oxidation, the TCA cycle, and the electron transport chain.

Glycolysis

The anaerobic first step of cellular respiration in the cytosol that breaks down one $6\text{-carbon}$ glucose molecule into two $3\text{-carbon}$ pyruvate molecules, yielding a net of $2\text{ ATP}$ and NADH.

Pyruvate Oxidation

The metabolic process occurring in the mitochondrial matrix where each $3\text{-carbon}$ pyruvate is converted into a $2\text{-carbon}$ acetyl CoA molecule, generating carbon dioxide ($\text{CO}_2$) and NADH.

Cori Cycle

The anaerobic recycling pathway in which pyruvate accepts hydrogens to form lactate in working muscle, lactate travels via the blood to the liver, and liver enzymes convert lactate back into glucose using ATP.

TCA Cycle (Citric Acid Cycle)

The final common metabolic pathway in the inner mitochondrial compartment where $2\text{-carbon}$ acetyl CoA joins with $4\text{-carbon}$ oxaloacetate to generate ATP (or GTP), NADH, $\text{FADH}_2$, and release $\text{CO}_2$, ultimately regenerating oxaloacetate.

Oxidative Phosphorylation

The pathway on the mitochondrial inner membrane where electron carriers pass electrons from NADH and $\text{FADH}_2$ to pump protons into the intermembrane space; protons flow back through ATP synthase to make ATP, while oxygen acts as the final electron acceptor to form $\text{H}_2\text{O}$.

Glucogenic Amino Acids

Amino acids that can be converted to pyruvate or enter the TCA cycle directly, allowing them to be utilized in the synthesis of glucose.

Ketogenic Amino Acids

Amino acids that are degraded directly into acetyl CoA, which can yield fat or ketone bodies, but cannot be used to synthesize glucose.

Gluconeogenesis

The metabolic pathway through which the body synthesizes glucose from noncarbohydrate sources, such as glucogenic amino acids and glycerol.

Ketone Bodies

Alternative fuel compounds (acetoacetate, acetone, and beta-hydroxybutyrate) produced by the liver from acetyl CoA during prolonged fasting or carbohydrate depletion to provide energy for the brain and nervous system.

Positive Energy Balance

A condition occurring when energy input exceeds energy expenditure ($\text{Energy Input} > \text{Energy Expenditure}$), leading to excess energy storage as body fat and resulting in weight gain.

Negative Energy Balance

A condition occurring when energy input is less than energy expenditure ($\text{Energy Input} < \text{Energy Expenditure}$), prompting the body to burn stored fuels and resulting in weight loss.

Carbohydrate-Insulin Model

A model of obesity proposing that high-glycemic-index diets drive increased insulin secretion and fat storage in adipose tissue, lowering circulating metabolic fuels and secondarily promoting hunger and overeating.

Metabolic Flexibility

The physiological capacity of the body to switch between different energy substrates (carbohydrates, fats, and proteins) to generate ATP based on demand and nutritional state.

Basal Metabolic Rate (BMR)

The rate of energy expenditure required to sustain involuntary, basic life functions at rest; it represents the largest component of total daily energy expenditure, accounting for $60\%\text{ to }75\%$.

Thermic Effect of Food (TEF)

The energy expended to digest, absorb, and metabolize ingested nutrients, comprising approximately $5\%\text{ to }10\%$ of total energy expenditure (with protein requiring about $30\%$ of its energy to process versus $5\%\text{ to }10\%$ for carbohydrates).

Physical Activity (PA)

The voluntary movement of skeletal muscles and support systems, representing the most variable and changeable component of energy expenditure ($15\%\text{ to }30\%$ of total output).

Estimated Energy Requirement (EER)

Formulas calculating total daily calorie requirements for adults based on sex, age in years, weight in kilograms, height in meters, and a physical activity (PA) coefficient.