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