Chapter 24 Key Terms

Key Terms in Metabolism and Nutrition

Absorptive State

  • Also called the fed state; the metabolic state occurring during the first few hours after ingesting food.

  • During this state, the body is digesting food and absorbing the nutrients.

Acetyl Coenzyme A (Acetyl CoA)

  • Definition: Starting molecule of the Krebs cycle.

Anabolic Hormones

  • Definition: Hormones that stimulate the synthesis of new, larger molecules.

Anabolic Reactions

  • Definition: Reactions that build smaller molecules into larger molecules.

ATP Synthase

  • Definition: A protein pore complex that creates ATP.

Basal Metabolic Rate (BMR)

  • Definition: The amount of energy expended by the body at rest.

Beta (β)-Hydroxybutyrate

  • Definition: Primary ketone body produced in the body.

Beta (β)-Oxidation

  • Definition: The process of fatty acid oxidation.

Bile Salts

  • Definition: Salts that are released from the liver in response to lipid ingestion. They surround the insoluble triglycerides to aid in their conversion to monoglycerides and free fatty acids.

Biosynthesis Reactions

  • Definition: Reactions that create new molecules, also called anabolic reactions.

Body Mass Index (BMI)

  • Definition: Relative amount of body weight compared to overall height.

  • Ranges:

    • 18–24.9: Normal weight

    • 25–29.9: Overweight

    • Greater than 30: Obese

Calorie

  • Definition: The amount of heat it takes to raise 1 kg (1000 g) of water by 1 °C.

Catabolic Hormones

  • Definition: Hormones that stimulate the breakdown of larger molecules.

Catabolic Reactions

  • Definition: Reactions that break down larger molecules into their constituent parts.

Cellular Respiration

  • Definition: The process of producing ATP from glucose oxidation via glycolysis, the Krebs cycle, and oxidative phosphorylation.

Cholecystokinin (CCK)

  • Definition: A hormone that stimulates the release of pancreatic lipase and the contraction of the gallbladder, facilitating digestion.

Chylomicrons

  • Definition: Vesicles containing cholesterol and triglycerides that transport lipids out of the intestinal cells into the lymphatic and circulatory systems.

Chymotrypsin

  • Definition: A pancreatic enzyme that digests protein.

Chymotrypsinogen

  • Definition: A proenzyme that is activated by trypsin into chymotrypsin.

Citric Acid Cycle (Krebs Cycle)

  • Definition: Converts pyruvate into CO2 and high-energy molecules FADH2, NADH, and ATP.

Conduction

  • Definition: The transfer of heat through physical contact.

Convection

  • Definition: The transfer of heat between the skin and air or water.

Elastase

  • Definition: A pancreatic enzyme that digests protein.

Electron Transport Chain (ETC)

  • Definition: An ATP production pathway where electrons pass through a series of oxidation-reduction reactions, forming water and producing a proton gradient.

Energy-Consuming Phase

  • Definition: The first phase of glycolysis in which two molecules of ATP are necessary to start the reaction.

Energy-Yielding Phase

  • Definition: The second phase of glycolysis, during which energy is produced.

Enterokinase

  • Definition: An enzyme located in the wall of the small intestine that activates trypsin.

Evaporation

  • Definition: The transfer of heat that occurs when water changes from a liquid to a gas.

FADH2

  • Definition: A high-energy molecule needed for glycolysis.

Fatty Acid Oxidation

  • Definition: The process of breaking down fatty acids into smaller chains, eventually forming acetyl CoA.

Flavin Adenine Dinucleotide (FAD)

  • Definition: A coenzyme used to produce FADH2.

Glucokinase

  • Definition: A cellular enzyme, found in the liver, that converts glucose into glucose-6-phosphate upon uptake.

Gluconeogenesis

  • Definition: The process of glucose synthesis from pyruvate or other molecules.

Glucose-6-Phosphate

  • Definition: Phosphorylated glucose produced in the first step of glycolysis.

Glycogen

  • Definition: Form that glucose assumes when stored.

Glycolysis

  • Definition: A series of metabolic reactions that breaks down glucose into pyruvate and produces ATP.

Hexokinase

  • Definition: A cellular enzyme, found in most tissues, that converts glucose into glucose-6-phosphate upon uptake.

Hydroxymethylglutaryl CoA (HMG CoA)

  • Definition: An acetyl CoA molecule created in the first step of the creation of ketone bodies.

Inactive Proenzymes

  • Definition: Forms in which proteases are stored and released to prevent inappropriate digestion of native proteins of the stomach, pancreas, and small intestine.

Insulin

  • Definition: A hormone secreted by the pancreas that stimulates the uptake of glucose into the cells.

Ketone Bodies

  • Definition: During fatty acid oxidation, these serve as alternative energy sources when glucose is limited, created when too much acetyl CoA is formed.

Krebs Cycle

  • Definition: Also called the citric acid cycle or the tricarboxylic acid cycle; converts pyruvate into CO2 and high-energy FADH2, NADH, and ATP molecules.

Lipogenesis

  • Definition: The synthesis of lipids that occurs in the liver or adipose tissues.

Lipolysis

  • Definition: The breakdown of triglycerides into glycerol and fatty acids.

Metabolic Rate

  • Definition: The amount of energy consumed minus the amount of energy expended by the body.

Metabolism

  • Definition: The sum of all catabolic and anabolic reactions that take place in the body.

Minerals

  • Definition: Inorganic compounds required by the body to ensure its proper functioning.

Monoglyceride

  • Definition: A lipid molecule consisting of a single fatty acid chain attached to a glycerol backbone.

Monosaccharide

  • Definition: The smallest, monomeric sugar molecule.

NADH

  • Definition: A high-energy molecule needed for glycolysis.

Nicotinamide Adenine Dinucleotide (NAD)

  • Definition: A coenzyme used to produce NADH.

Oxidation

  • Definition: The loss of an electron.

Oxidation-Reduction Reaction (Redox Reaction)

  • Definition: A pair of reactions in which an electron is passed from one molecule to another, oxidizing one and reducing the other.

Oxidative Phosphorylation

  • Definition: The process that converts high-energy NADH and FADH2 into ATP.

Pancreatic Lipases

  • Definition: Enzymes released from the pancreas that digest lipids in the diet.

Pepsin

  • Definition: An enzyme that begins to break down proteins in the stomach.

Polysaccharides

  • Definition: Complex carbohydrates made up of many monosaccharides.

Postabsorptive State

  • Also called the fasting state; the metabolic state occurring after digestion when food is no longer the body’s source of energy and it must rely on stored glycogen.

Proteolysis

  • Definition: The process of breaking proteins into smaller peptides.

Pyruvate

  • Definition: A three-carbon end product of glycolysis and the starting material that is converted into acetyl CoA that enters the Krebs cycle.

Radiation

  • Definition: The transfer of heat via infrared waves.

Reduction

  • Definition: Gaining of an electron.

Salivary Amylase

  • Definition: A digestive enzyme found in saliva that begins the digestion of carbohydrates in the mouth.

Secretin

  • Definition: A hormone released in the small intestine to aid in digestion.

Sodium Bicarbonate

  • Definition: An anion released into the small intestine to neutralize the pH of the food from the stomach.

Terminal Electron Acceptor

  • Definition: Oxygen, the recipient of the free hydrogen at the end of the electron transport chain.

Thermoneutral

  • Definition: The external temperature at which the body does not expend any energy for thermoregulation, approximately 84 °F.

Thermoregulation

  • Definition: The process of regulating the temperature of the body.

Transamination

  • Definition: The transfer of an amine group from one molecule to another, which is a method to turn nitrogen waste into ammonia.

Tricarboxylic Acid Cycle (TCA)

  • Definition: Also called the Krebs cycle or the citric acid cycle; converts pyruvate into CO2 and produces high-energy FADH2, NADH, and ATP molecules.

Triglycerides

  • Definition: Lipids, or fats, consisting of three fatty acid chains attached to a glycerol backbone.

Trypsin

  • Definition: A pancreatic enzyme that activates chymotrypsin and digests protein.

Trypsinogen

  • Definition: Proenzyme form of trypsin.

Urea Cycle

  • Definition: The process that converts potentially toxic nitrogen waste into urea for elimination through the kidneys.

Vitamins

  • Definition: Organic compounds required by the body to perform biochemical reactions, such as metabolism, growth, and cell function.