Nutrition, Metabolism, and Energy Balance Flashcards

This flashcard set covers the essential vocabulary related to nutrition, metabolic pathways, energy production, and the body's absorptive and postabsorptive states as described in Chapter 23.

Nutrient

A substance in food needed for growth, maintenance, and repair.

Macronutrients

The three major nutrients that make up the bulk of ingested food: carbohydrates, lipids, and proteins.

Micronutrients

Nutrients required only in small amounts, consisting of vitamins and minerals.

Essential nutrients

$45$–$50$ nutrients that must be eaten because the body cannot synthesize them from other nutrients.

Kilocalorie (kcal)

The amount of heat needed to raise the temperature of $1$ kilogram of $H_2O$ by $1\,^{\circ}C$; also referred to as one dietary "Calorie."

Insoluble fiber

Cellulose found in vegetables that provides roughage for the diet.

Soluble fiber

Pectin found in apples and citrus fruits that reduces blood cholesterol levels.

Glucose

The fuel most used by cells to make ATP; it is the exclusive energy source for neurons and RBCs.

Triglycerides

The most abundant form of lipids, consisting of neutral fats found in saturated and unsaturated sources.

Linoleic acid

An essential omega-6 fatty acid and component of lecithin that the liver cannot synthesize.

Linolenic acid

An essential omega-3 fatty acid that must be obtained from the diet because the liver cannot synthesize it.

All-or-none rule

The principle that all amino acids needed for a specific protein must be present at the same time for protein synthesis to occur; otherwise, they are used for energy.

Anabolism

The synthesis of large molecules from small ones, such as the synthesis of proteins from amino acids.

Catabolism

The hydrolysis of complex structures to simpler ones, such as the breakdown of proteins into amino acids.

Cellular respiration

The catabolic breakdown of food fuels whereby energy is captured to form ATP in cells.

Phosphorylation

The process where enzymes shift high-energy phosphate groups of ATP to other molecules, activating them for cellular functions.

Oxidation reactions

Reactions involving the gain of oxygen or the loss of hydrogen atoms and their associated electrons.

Oxidation-reduction (redox) reactions

Coupled reactions where oxidized substances lose electrons and energy, while reduced substances gain electrons and energy.

Dehydrogenases

Enzymes that catalyze the removal of hydrogen atoms during redox reactions.

Glycolysis

A $10$-step anaerobic pathway in the cytosol that breaks down one glucose molecule into two pyruvic acid molecules.

Citric acid cycle (Krebs cycle)

An aerobic pathway in the mitochondrial matrix fueled by pyruvic acid and fatty acids that produces $CO_2$, reduced coenzymes, and ATP.

Decarboxylation

A step in the transitional phase where $1$ carbon from pyruvic acid is removed to produce $CO_2$ gas.

Acetyl coenzyme A (acetyl CoA)

The molecule formed when acetic acid combines with coenzyme A, serving as the entry point for the citric acid cycle.

Electron transport chain (ETC)

Phase 1 of oxidative phosphorylation that uses high-energy electrons from food fuels to create a proton ($H^+$) gradient across the mitochondrial membrane.

Chemiosmosis

Phase 2 of oxidative phosphorylation that harnesses the energy of the proton gradient to synthesize ATP.

ATP synthase

A mitochondrial membrane channel protein that acts as a rotary motor to join inorganic phosphate ($P_i$) to ADP, forming ATP.

Glycogenesis

The process of forming glycogen from excess glucose, primarily occurring in the liver and skeletal muscle cells.

Glycogenolysis

The breakdown of glycogen into glucose-$1$-phosphate (and eventually glucose) in response to low blood glucose levels.

Gluconeogenesis

The process of forming new glucose from noncarbohydrate sources like glycerol and amino acids, occurring in the liver.

Beta oxidation

The mitochondrial process that converts fatty acids into acetyl CoA molecules.

Lipolysis

The breakdown of stored fats into glycerol and fatty acids.

Ketogenesis

The liver's conversion of accumulated acetyl CoA into ketone bodies when oxaloacetic acid is unavailable.

Absorptive state

Also called the fed state; the period lasting about $4$ hours after eating when nutrients are being absorbed and anabolism exceeds catabolism.

Postabsorptive state

Also called the fasting state; the period when the GI tract is empty and the body breaks down reserves to maintain blood glucose levels.

Glucose sparing

The increased use of noncarbohydrate fuel sources (like fat) to conserve glucose for the brain during fasting.

Insulin

A hypoglycemic hormone that enhances glucose oxidation, glycogen formation, and protein synthesis while inhibiting gluconeogenesis.

Glucagon

A hyperglycemic hormone that promotes glycogenolysis, gluconeogenesis, and lipolysis to raise blood glucose levels.