Nutrition: Concepts and Controversies 12th Edition

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Chapter 6 Definitions

proteins

compounds composed of carbon, hydrogen, oxygen, and nitrogen and arranged as strands of amino acids. Some amino acids also contain the element sulfur.

amino acids

the building blocks of protein. Each has an amine group at one end, an acid group at the other, and a distinctive side chain.

amine group

the nitrogen- containing portion of an amino acid.

side chain

the unique chemical structure attached to the backbone of each amino acid that differentiates one amino acid from another.

essential amino acids

amino acids that either cannot be synthesized at all by the body or cannot be synthesized in amounts suf- ficient to meet physiological need. Also called indispensable amino acids.

conditionally essential amino acid

an amino acid that is normally non- essential but must be supplied by the diet in special circumstances when the need for it exceeds the body's ability to produce it.

peptide bond

a bond that connects one amino acid with another, forming a link in a protein chain.

collagen

a type of body protein from which connective tissues such as scars, tendons, ligaments, and the foundations of bones and teeth are made.

enzymes

proteins that facilitate chemical reactions without being changed in the process; protein catalysts.

hemoglobin

the globular protein of red blood cells, whose iron atoms carry oxygen around the body via the bloodstream.

denaturation

the irreversible change in a protein's folded shape brought about by heat, acids, bases, alcohol, salts of heavy metals, or other agent

polypeptides

protein fragments of many (more than 10) amino acids bonded together ( poly means "many"). A peptide is a strand of amino acids. A strand of between 4 and 10 amino acids is called an oligopeptide.

dipeptides

protein frag- ments that are 2 amino acids long (di means "two").

tripeptides

protein fragments that are 3 amino acids long (tri means "three")

protein turnover

the continuous break- down and synthesis of body proteins involving the recycling of amino acids.

catalyst

a substance that speeds the rate of a chemical reaction without itself being permanently altered in the process.

hormones

chemical messengers secreted by a number of body organs in response to conditions that require regulation. Each hormone affects a specific organ or tissue and elicits a specific response. Also defined in Chapter 3.

thyroxine

a principle peptide hormone of the thyroid gland that regulates the body's rate of energy use.

serotonin

a compound related in structure to (and made from) the amino acid tryptophan. It serves as one of the brain's principal neurotransmitters.

immunity

protection from or resistance to a disease or infection by development of anti- bodies and by the actions of cells and tissues in response to a threat.

fluid and electrolyte balance

the distribution of fluid and dissolved par- ticles among body compartments (see also Chapter 8).

edema

swelling of body tis- sue caused by leakage of fluid from the blood vessels; seen in protein deficiency (among other conditions).

acids

compounds that release hydrogens in a watery solution.

bases

compounds that accept hydrogens from solutions.

acid-base balance

equilibrium between acid and base concentrations in the body fluids.

buffers

compounds that help keep a solu- tion's acidity or alkalinity constant.

acidosis

the condition of excess acid in the blood, indicated by a below-normal pH (osis means "too much in the blood").

alkalosis

the condition of excess base in the blood, indicated by an above-normal blood pH (alka means "base"; osis means "too much in the blood").

urea

the principal nitrogen- excretion product of protein metabolism; generated mostly by removal of amine groups from unneeded amino acids or from amino acids being sacrificed to a need for energy.

nitrogen balance

the amount of nitrogen
consumed compared with the amount excreted in a given time period.

high-quality proteins

dietary proteins containing all the essential amino acids in rela- tively the same amounts that human beings require. They may also contain nonessential amino acids.

limiting amino acid

an essential amino acid that is present in dietary protein in an insufficient amount, thereby limiting the body's ability to build protein.

complementary proteins

two or more proteins whose amino acid assortments complement each other in such a way that the essential amino acids missing from one are supplied by the other.

mutual supplementation

the strategy of combining two incomplete protein sources so that the amino acids in one food make up for those lacking in the other food. Such protein combinations are sometimes called complementary proteins.

legumes

plants of the bean, pea, and lentil family that have roots with nodules containing special bacteria. These bacteria can trap nitrogen from the air in the soil and make it into compounds that become part of the plant's seeds. The seeds are rich in protein compared with those of most other plant foods. Also defined in Chapter 1.

fufu

a low-protein staple food that provides abundant starch energy to many of the world's people; made by pounding or grinding root vegetables or refined grains and cooking them to a smooth semisolid consistency.

protein-energy malnutrition (PEM)

the world's most widespread malnu- trition problem, including both marasmus and kwashiorkor and states in which they overlap; also called protein-calorie malnutrition (PCM).

hunger

the physiological craving for food; the progressive discomfort, illness, and pain resulting from the lack of food. See also Chap- ters 9 and 15.

marasmus

a form of PEM related to protein malnutrition and infections, with a set of recognizable symptoms, such as edema.

kwashiorkor

a form of PEM related to protein malnutrition and infections, with a set of recognizable symptoms, such as edema.

dysentery

an infection of the digestive tract that causes diarrhea.

homocysteine

an amino acid produced as an intermediate compound during amino acid metabolism. Its buildup in the blood is associated with deficiencies of B vitamins and may increase the risk of diseases. See also Chapter 7.

osteoporosis

a disease of older persons characterized by porous and fragile bones that easily break, leading to pain, infirmity, and death. Also defined in Chapter 8.

antibodies

large proteins of the blood, produced by the immune system in response to an invasion of the body by foreign substances. Also defined in Chapter 3.

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