Key Terms

absorptive state

also called the fed state; the metabolic state occurring during the first few hours after ingesting food in which the body is digesting food and absorbing the nutrients

acetyl coenzyme A (acetyl CoA)

starting molecule of the Krebs cycle

anabolic hormones

hormones that stimulate the synthesis of new, larger molecules

anabolic reactions

reactions that build smaller molecules into larger molecules

ATP synthase

protein pore complex that creates ATP

basal metabolic rate (BMR)

amount of energy expended by the body at rest

beta (β)-hydroxybutyrate

primary ketone body produced in the body

beta (β)-oxidation

fatty acid oxidation

bile salts

salts that are released from the liver in response to lipid ingestion and surround the insoluble triglycerides to aid in their conversion to monoglycerides and free fatty acids

biosynthesis reactions

reactions that create new molecules, also called anabolic reactions

body mass index (BMI)

relative amount of body weight compared to the overall height; a BMI ranging from 18–24.9 is considered normal weight, 25–29.9 is considered overweight, and greater than 30 is considered obese

calorie

amount of heat it takes to raise 1 kg (1000 g) of water by 1 °C

catabolic hormones

hormones that stimulate the breakdown of larger molecules

catabolic reactions

reactions that break down larger molecules into their constituent parts

cellular respiration

production of ATP from glucose oxidation via glycolysis, the Krebs cycle, and oxidative phosphorylation

cholecystokinin (CCK)

hormone that stimulates the release of pancreatic lipase and the contraction of the gallbladder to release bile salts

chylomicrons

vesicles containing cholesterol and triglycerides that transport lipids out of the intestinal cells and into the lymphatic and circulatory systems

chymotrypsin

pancreatic enzyme that digests protein

chymotrypsinogen

proenzyme that is activated by trypsin into chymotrypsin

citric acid cycle

also called the Krebs cycle or the tricarboxylic acid cycle; converts pyruvate into CO₂ and high-energy FADH₂, NADH, and ATP molecules

conduction

transfer of heat through physical contact

convection

transfer of heat between the skin and air or water

elastase

pancreatic enzyme that digests protein

electron transport chain (ETC)

ATP production pathway in which electrons are passed through a series of oxidation-reduction reactions that forms water and produces a proton gradient

energy-consuming phase

first phase of glycolysis, in which two molecules of ATP are necessary to start the reaction

energy-yielding phase

second phase of glycolysis, during which energy is produced

enterokinase

enzyme located in the wall of the small intestine that activates trypsin

evaporation

transfer of heat that occurs when water changes from a liquid to a gas

FADH₂

high-energy molecule needed for glycolysis

fatty acid oxidation

breakdown of fatty acids into smaller chain fatty acids and acetyl CoA

flavin adenine dinucleotide (FAD)

coenzyme used to produce FADH₂

glucokinase

cellular enzyme, found in the liver, which converts glucose into glucose-6-phosphate upon uptake into the cell

gluconeogenesis

process of glucose synthesis from pyruvate or other molecules

glucose-6-phosphate

phosphorylated glucose produced in the first step of glycolysis

glycogen

form that glucose assumes when it is stored

glycolysis

series of metabolic reactions that breaks down glucose into pyruvate and produces ATP

hexokinase

cellular enzyme, found in most tissues, that converts glucose into glucose-6-phosphate upon uptake into the cell

hydroxymethylglutaryl CoA (HMG CoA)

molecule created in the first step of the creation of ketone bodies from acetyl CoA

inactive proenzymes

forms in which proteases are stored and released to prevent the inappropriate digestion of the native proteins of the stomach, pancreas, and small intestine

insulin

hormone secreted by the pancreas that stimulates the uptake of glucose into the cells

ketone bodies

alternative source of energy when glucose is limited, created when too much acetyl CoA is created during fatty acid oxidation

Krebs cycle

also called the citric acid cycle or the tricarboxylic acid cycle, converts pyruvate into CO₂ and high-energy FADH₂, NADH, and ATP molecules

lipogenesis

synthesis of lipids that occurs in the liver or adipose tissues

lipolysis

breakdown of triglycerides into glycerol and fatty acids

metabolic rate

amount of energy consumed minus the amount of energy expended by the body

metabolism

sum of all catabolic and anabolic reactions that take place in the body

minerals

inorganic compounds required by the body to ensure proper function of the body

monoglyceride molecules

lipid consisting of a single fatty acid chain attached to a glycerol backbone

monosaccharide

smallest, monomeric sugar molecule

NADH

high-energy molecule needed for glycolysis

nicotinamide adenine dinucleotide (NAD)

coenzyme used to produce NADH

oxidation

loss of an electron

oxidation-reduction reaction

(also, redox reaction) pair of reactions in which an electron is passed from one molecule to another, oxidizing one and reducing the other

oxidative phosphorylation

process that converts high-energy NADH and FADH₂ into ATP

pancreatic lipases

enzymes released from the pancreas that digest lipids in the diet

pepsin

enzyme that begins to break down proteins in the stomach

polysaccharides

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

process of breaking proteins into smaller peptides

pyruvate

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

radiation

transfer of heat via infrared waves

reduction

gaining of an electron

salivary amylase

digestive enzyme that is found in the saliva and begins the digestion of carbohydrates in the mouth

secretin

hormone released in the small intestine to aid in digestion

sodium bicarbonate

anion released into the small intestine to neutralize the pH of the food from the stomach

terminal electron acceptor

oxygen, the recipient of the free hydrogen at the end of the electron transport chain

thermoneutral

external temperature at which the body does not expend any energy for thermoregulation, about 84 °F

thermoregulation

process of regulating the temperature of the body

transamination

transfer of an amine group from one molecule to another as a way to turn nitrogen waste into ammonia so that it can enter the urea cycle

tricarboxylic acid cycle (TCA)

also called the Krebs cycle or the citric acid cycle; converts pyruvate into CO₂ and high-energy FADH₂, NADH, and ATP molecules

triglycerides

lipids, or fats, consisting of three fatty acid chains attached to a glycerol backbone

trypsin

pancreatic enzyme that activates chymotrypsin and digests protein

trypsinogen

proenzyme form of trypsin

urea cycle

process that converts potentially toxic nitrogen waste into urea that can be eliminated through the kidneys

vitamins

organic compounds required by the body to perform biochemical reactions like metabolism and bone, cell, and tissue growth