Chapter 6: Proteins and Amino Acids

amino acids

The building blocks of proteins. Each contains a central carbon atom bound to a hydrogen atom, an amino group, an acid group, and a side chain.

essential or indispensable amino acids

Amino acids that cannot be synthesized by the human body in sufficient amounts to meet needs and therefore must be included in the diet.

nonessential or dispensable amino acids

Amino acids that can be synthesized by the human body in sufficient amounts to meet needs.

transamination

The process by which an amino group from one amino acid is tranferred to a carbon compound to form a new amino acid.

conditionally essential amino acids

Amino acids that are essential in the diet only under certain conditions or at certain times of life.

dipeptide

Two amino acids linked by a peptide bound.

tripeptide

Three amino acids linked by peptide bonds.

polypeptide

A chain of three or more amino acids linked by peptide bonds.

denaturation

The alteration of a protein's three-dimensional structure.

pepsin

Breaks proteins into polypeptides and amino acids in stomach.

trypsin and chymotrypsin

Breaks polypeptides into tripeptides, dipeptides, and amino acids in small intestine.

anaphalaxis

An immediate and severe allergic reaction to a substance (e.x., food or drugs). Symptoms include breathing difficulty, loss of consciousness, and a drop in blood pressure and can be fatal.

amino acid pool

All of the amino acids in body tissues and fluids that are available for use by the body.

protein turnover

The continuous synthesis and breakdown of body proteins.

gene

A length of DNA containing the information needed to synthesize RNA or polypeptide chains.

transcription

The process of copying the information in DNA to a molecule of mRNA.

translation

The process of translating the mRNA code into the amino acid sequence of a polypeptide chain.

gene expression

The events of protein synthesis in which the information coded in a gene is used to synthesize a product; either a protein or a molecule.

limiting amino acid

The essential amino acid that is available in the lowest concentration in relation to the body's needs.

deamination

The removal of the amino group from an amino acid.

urea

A nitrogen-containing waste product formed from the breakdown of amino acids that is excreted in the urine.

antibodies

Proteins produced by the body's immune system that recognize foreign substances in the body and help destroy them.

pH

A measure of acidity.

protein-energy malnutrition (PEM)

A condition characterized by wasting and an increased susceptibility to infection that results from the long-term consumption of insufficient amounts of energy and protein to meed needs.

kwashiorkor

A form of protein-energy malnutrition in which only protein is deficient.

marasmus

A form of protein-energy malnutrition in which a deficiency of energy in the diet causes severe body wasting.

phenylketonuria (PKU)

An inherited disease in which the body cannot metabolize the amino acid phenylalanine. If the disease is untreated, toxic by-products called phenylketones accumulate in the blood and interfere with brain development.

celiac disease or gluten intolerance

A disorder that causes damage to the intestines when the protein gluten is eaten.

nitrogen balance

The amount of nitrogen consumed in the diet compared with the amount excreted by the body over a given period.

protein quality

A measure of how efficiently a protein in the diet can be used to make body proteins.

complete dietary protein

Protein that provides essential amino acids in the proportions needed to support protein synthesis.

incomplete dietary protein

Protein that is deficient in one or more essential amino acids relative to body needs.

chemical or amino acid score

A measure of protein quality determined by comparing the essential amino acid content of the protein in a food with that in a reference protein. The lowest amino acid ratio calculated is the chemical score.

protein digestibility-corrected amino acid score (PDCAAS)

A measure of protein quality that reflects a protein's digestibility as well as the proportions of amino acids it provides.

protein efficiency ratio

A measure of protein quality determined by comparing the weight gain of a laboratory animal fed a test protein with weight gain of an animal fed a reference protein.

net protein utilization and biological value

Measures how well a protein is used by the body for growth and maintenance.

protein complementation

Combines foods containing proteins with different limiting amino acids in order to improve the protein quality of the diet as a whole.

vegan

A pattern of food intake that eliminates all animal products.

vegetarianism

A pattern of food intake that eliminates some or all animal products.