Energy Metabolism, Cellular Respiration, Nutrition, and Energy Balance

Comprehensive vocabulary review flashcards covering cellular respiration, carbohydrate, lipid, and protein catabolism, metabolic regulation, sports nutrition, energy balance, and body composition assessment.

Oxidation

A chemical reaction biochemically defined as the loss of hydrogen or the gain of oxygen.

Reduction

A chemical reaction biochemically defined as the gain of hydrogen or the loss of oxygen.

Redox Reaction

Coupled reactions where oxidation and reduction occur simultaneously to transfer chemical energy to $ATP$ and prevent the formation of destructive reactive oxidative species (ROS).

Decarboxylation Reaction

A chemical reaction used in the catabolism of energy-yielding nutrients that removes a carboxyl group and releases carbon dioxide ($CO_2$).

Metabolism

The entire network of chemical processes and biochemical reactions taking place within cells to sustain life.

Anabolic Pathway

A metabolic sequence that utilizes energy to synthesize larger, complex molecules from simpler precursors (e.g., $Glucose + ATP \rightarrow Glycogen$).

Catabolic Pathway

A metabolic sequence that breaks down larger molecules into smaller compounds to harvest and produce energy (e.g., $Glucose \rightarrow Pyruvate + ATP$).

Coenzyme

A non-protein organic compound necessary for the catalytic functioning of an enzyme, such as $NAD^+$ (derived from niacin), $FAD$ (derived from riboflavin), and Coenzyme A (derived from pantothenic acid).

Adenosine Triphosphate (ATP)

The primary energy currency of the body that traps energy within high-energy phosphate-to-phosphate bonds; the human body maintains a pool of approximately $0.22\text{ lb}$ and uses about $88\text{ lb}$ daily.

Glycolysis

A catabolic pathway located in the cytosol that converts one glucose molecule into two molecules of pyruvate, producing a net yield of $+2\text{ ATP}$ and $+2\text{ NADH}$.

Transition Reaction

An irreversible reaction in the mitochondrial matrix catalyzed by the pyruvate dehydrogenase complex that converts two pyruvate molecules into two acetyl-CoA, releasing two $CO_2$ and producing $2\text{ NADH}$.

Citric Acid Cycle (TCA Cycle)

A circular metabolic pathway in the mitochondrial matrix where acetyl-CoA combines with oxaloacetate to form citrate, yielding $4\text{ CO}_2$, $6\text{ NADH}$, $2\text{ FADH}_2$, and $2\text{ ATP}$ per glucose molecule.

Oxidative Phosphorylation (OXPHOS)

A metabolic process in the inner mitochondrial membrane where electrons from $NADH$ and $FADH_2$ travel through cytochromes to pump protons into the intermembrane space, driving $ATP$ synthase with oxygen ($O_2$) as the final electron acceptor.

Anaerobic Glycolysis

A pathway utilized when oxygen is deficient or in cells lacking mitochondria (such as erythrocytes), where cytosolic pyruvate is reduced to lactate to re-oxidize $NADH$ back to $NAD^+$, generating an energy yield of $2\text{ ATP}$ per glucose.

Cori Cycle

A inter-organ metabolic pathway wherein lactate produced by exercising muscle is released into the blood, transported to the liver to be converted back into glucose via gluconeogenesis at a cost of $6\text{ ATP}$, and returned to the muscle.

Lipogenesis

The biochemical synthesis of triglycerides from excess dietary glucose and amino acids taking place predominantly in the liver.

Lipolysis

The metabolic breakdown of stored adipose triglycerides into free fatty acids and glycerol.

Carnitine

A compound synthesized in the liver and predominantly stored in muscle ($900\%$) that shuttles activated fatty acids across the mitochondrial membrane for beta-oxidation.

Beta-Oxidation

A metabolic pathway in the mitochondrial matrix that successively cleaves fatty acids into two-carbon acetyl-CoA units while producing $NADH$ and $FADH_2$, yielding approximately $7\text{ ATP}$ per carbon compared to $5\text{ ATP}$ per carbon from glucose.

Oxaloacetate

A four-carbon citric acid cycle intermediate synthesized from pyruvate that must be constantly replenished from carbohydrate catabolism for acetyl-CoA to enter the citric acid cycle.

Ketogenesis

A spillover pathway occurring in liver mitochondria during low glucose availability or fasting, where excess acetyl-CoA molecules condense into ketone bodies (acetoacetate, acetone, and D-$\beta$-hydroxybutyrate).

Diabetic Ketoacidosis (DKA)

A severe, potentially fatal complication of type 1 diabetes where absolute lack of insulin prevents glucose uptake, leading to uncontrolled lipolysis, oxaloacetate depletion, severe ketone accumulation, electrolyte loss, and dehydration.

Ketogenic Diet

An aggressive dietary protocol consisting of $75-80\%$ fat, $10-20\%$ protein, and only $5-10\%$ carbohydrates, designed to empty glycogen stores and induce ketosis.

Deamination

The initial step of amino acid catabolism in the liver, involving the removal of the nitrogen-containing amine group to produce toxic ammonia ($NH_3$) and a carbon skeleton.

Transamination

The enzymatic transfer of an amino group from an amino acid to a carbon skeleton to form a new amino acid, a reaction that requires vitamin $B_6$.

Glucogenic Amino Acids

Amino acids whose catabolized carbon skeletons yield pyruvate or citric acid cycle intermediates (such as oxaloacetate), allowing them to be converted into glucose via gluconeogenesis.

Ketogenic Amino Acids

Amino acids whose catabolized carbon skeletons yield acetyl-CoA; because the pyruvate dehydrogenase reaction is irreversible, they cannot be converted into glucose.

Gluconeogenesis

An anabolic pathway occurring in the cytosol of liver and kidney cells that synthesizes glucose from non-carbohydrate substrates, specifically glucogenic amino acids, glycerol, and lactate.

Urea

A non-toxic compound synthesized in the liver from toxic ammonia released during amino acid deamination, which is subsequently excreted by the kidneys in urine.

Alcohol Dehydrogenase (ADH)

The primary liver and stomach enzyme that oxidizes ethanol into toxic acetaldehyde while reducing $NAD^+$ to $NADH + H^+$.

Microsomal Ethanol Oxidizing System (MEOS)

An inducible secondary metabolic pathway that assists in oxidizing ethanol to acetaldehyde in the liver specifically during periods of heavy or excessive alcohol intake.

Insulin

An anabolic hormone secreted in response to elevated blood glucose that promotes cellular glucose uptake, glycogenesis, lipogenesis, and amino acid uptake while blocking fatty acid release from adipose tissue.

Glucagon

A catabolic hormone secreted during periods of low blood glucose that stimulates glycogenolysis, gluconeogenesis, and lipolysis while reducing cellular glucose uptake.

Postprandial State

The fed metabolic period lasting up to $4-5\text{ hours}$ after a meal, dominated by insulin, where dietary macronutrients are consumed for energy production and stored in anabolic reserves.

Postabsorptive State

The metabolic period occurring roughly $6-12\text{ hours}$ after the last meal (overnight fast), driven by rising glucagon, where blood glucose is sustained by hepatic glycogenolysis, lipolysis, and gluconeogenesis.

Metabolic Switch

The point during negative energy balance (occurring beyond $12\text{ hours}$ of fasting) when liver glycogen stores deplete, fatty acids become the primary fuel, and ketone body concentrations rise.

ATP-Phosphocreatine (ATP-PC) System

An immediate anaerobic energy system that uses intramuscular phosphocreatine to rapidly regenerate $ATP$ from $ADP$, sustaining maximal all-out physical exertion for up to $10-20\text{ seconds}$.

GLUT4 Translocation

The movement of glucose transporter type 4 vesicles to the cell membrane, triggered independently by both insulin and skeletal muscle contractions to increase exercise-induced glucose uptake up to 50-fold.

Relative Energy Deficiency in Sport (RED-S)

A syndrome of impaired physiological function (affecting metabolic rate, bone health, immunity, protein synthesis, and cardiovascular health) resulting from low energy availability where caloric intake does not match training energy expenditure.

Creatine Monohydrate

An ergogenic aid dosed at $3-5\text{ g/day}$ that increases intramuscular phosphocreatine stores, enhancing power and strength during high-intensity, short-duration athletic performance.

Sodium Bicarbonate

An ergogenic buffering compound (baking soda) supplemented at roughly $300\text{ mg/kg BW}$ to reduce muscle fatigue, but frequently limited by severe gastrointestinal distress.

Energy Balance

The equilibrium between energy intake (caloric energy from food) and energy expenditure (basal metabolism, physical activity, thermogenesis, and the thermic effect of food).

Basal Metabolic Rate (BMR)

The minimum energy expended each day to maintain vital organ function, measured in a rested, fasting state ($12\text{ hours}$) in a warm, quiet environment; constitutes roughly $60\%$ of total energy expenditure in sedentary individuals.

Resting Metabolic Rate (RMR)

The energy expended while resting comfortably in a quiet, warm environment, measured under less stringent criteria than BMR (e.g., $3-4\text{ hours}$ fasting), yielding values roughly $6\%$ higher than BMR.

Non-Exercise Activity Thermogenesis (NEAT)

The energy expended for all spontaneous physical activities outside of structured exercise, such as fidgeting, maintaining posture, standing, walking, and household tasks.

Thermic Effect of Food (TEF)

The energetic cost required to digest, absorb, transport, store, and metabolize ingested nutrients, accounting for approximately $5-10\%$ of daily energy intake (highest for protein at $20-30\%$).

Brown Adipose Tissue (BAT)

A thermogenic fat tissue packed with mitochondria and uncoupling protein 1 (UCP1) that expends chemical energy directly as heat in response to cold exposure.

Body Mass Index (BMI)

A clinical screening metric calculating weight relative to height ($\frac{\text{Body Weight (kg)}}{[\text{Height (m)}]^2}$ or $\frac{\text{Body Weight (lb)} \times 703}{[\text{Height (inches)}]^2}$) with categories: underweight ($<18.5$), healthy ($18.5-<25$), overweight ($25-<30$), and obese ($\ge 30$).

Visceral Fat

Adipose tissue deposited intra-abdominally surrounding internal organs, which poses the greatest metabolic risk for cardiovascular disease and type 2 diabetes.

Homeostatic Pathway

A neuroendocrine regulatory system coordinated by the hypothalamus that integrates hormonal signals (such as leptin and ghrelin) and energy expenditure to regulate energy intake.

Hedonic Pathway

A reward-driven brain circuitry that responds to sensory, cognitive, and environmental food cues; in an obesogenic environment with food abundance, it frequently overrides homeostatic appetite regulation.

Orthorexia

An eating disorder characterized by an unhealthy, obsessive fixation on consuming only 'pure' or 'healthy' foods, frequently leading to malnutrition, social isolation, and nutrient deficiencies.