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amino acid pool

the supply of amino acids derived from either food proteins or body proteins that collect in the cells and circulating blood and stand ready to be incorporated in proteins and other compounds or used for energy.

amino acid scoring

a method of evaluating protein quality by comparing a test protein's amino acid pattern with that of a reference protein, sometimes called chemical scoring.

amino acids

building blocks of proteins; each contains an amino group, an acid group, a hydrogen atom, and a distinctive side group attached to a central carbon atom.

biological value (BV)

the amount of protein nitrogen that is retained for growth and maintenance, expressed as a percentage of the protein nitrogen that has been digested and absorbed; a measure of protein quality.

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.

complete protein

a protein containing all the amino acids essential in human nutrition in amounts adequate for human use.

conditionally essential amino acid

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

Deamination

removal of the amino (NH2) group from a compound such as an amino acid.

Denaturation

the change in a protein's shape brought about by heat, acid, base, alcohol, heavy metals, or other agents.

Dipeptide

two amino acids bonded together.

Enzymes

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

essential amino acids

amino acids that the body cannot synthesize in amounts sufficient to meet physiological needs.

high-quality protein

an easily digestible, complete protein.

Hormones

chemical messengers. Hormones are secreted by a variety of endocrine glands in response to altered conditions in the body. Each travels to one or more specific target tissues or organs, where it elicits a specific response.

Kwashiorkor

a form of PEM that results from either inadequate protein intake, or more commonly, from infections.

limiting amino acid

the essential amino acid found in the shortest supply relative to the amounts needed for protein synthesis in the body.

Marasmus

a form of PEM that results from a severe deprivation, or impaired absorption, of energy, protein, vitamins, and minerals.

negative nitrogen balance

N in < N out.

net protein utilization (NPU)

the amount of protein nitrogen that is retained from a given amount of protein nitrogen eaten; a measure of protein quality.

nitrogen balance

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

nitrogen equilibrium

zero nitrogen balance; N in = N out.

nonessential amino acids

amino acids that the body can synthesize.

peptide bond

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

positive nitrogen balance

N in > N out.

protein digestibility

a measure of the amount of amino acids absorbed from a given protein intake.

protein efficiency ratio (PER)

a measure of protein quality assessed by determining how well a given protein supports weight gain in growing rats; used to establish the protein quality for infant formulas and baby foods.

protein turnover

the degradation and synthesis of endogenous protein.

protein-digestibility-corrected amino acid score (PDCAAS)

a measure of protein quality assessed by comparing the amino acid balance of a food protein with the amino acid requirements of preschool-aged children and then correcting for the true digestibility of protein

protein-energy malnutrition (PEM)

also called protein-kcalorie malnutrition (PCM). A deficiency of both protein and energy; the world's most widespread malnutrition problem, including kwashiorkor, marasmus, and instances in which they overlap.

Proteins

compounds composed of carbon, hydrogen, oxygen, and nitrogen atoms, arranged into amino acids linked in a chain. Some amino acids also contain sulfur atoms.

reference protein

standard against which to measure the quality of other proteins.

Tripeptide

three amino acids bonded together.

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