Proteins and Amino Acids

Vocabulary practice flashcards covering amino acid structure, protein synthesis, physiological functions, protein quality, dietary standards, vegetarian diets, and protein-energy malnutrition.

Amino acids

The building blocks of proteins, each composed of a central carbon bonded to an amino group, an acid (carboxyl) group, a hydrogen group, and a variable R group (side chain).

Nitrogen

The chemical element unique to protein among the energy-yielding macronutrients, in addition to carbon, hydrogen, and oxygen.

Essential amino acids

Amino acids that cannot be synthesized by the human body in sufficient amounts and must be obtained through the diet: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

Nonessential amino acids

Amino acids that can normally be synthesized by the body in adequate quantities.

Conditionally essential amino acids

Nonessential amino acids that the body cannot make under specific physiological conditions or illness, requiring them to be supplied by the diet.

Transamination

The biochemical process in which an amine group is transferred from one molecule to another to produce a nonessential amino acid.

Peptide bond

A covalent chemical link connecting the acid group of one amino acid to the amino group of another, releasing water during formation to create polypeptides.

Denaturation

The process in which a protein's natural three-dimensional structure is altered or unfolded by factors such as heat, acid, enzymes, agitation, or alcohol.

Albumin

A major transport and blood protein responsible for maintaining proper fluid balance between the bloodstream and interstitial spaces.

Edema

The accumulation of fluid in interstitial body tissues, which develops when blood albumin concentration becomes abnormally low.

Antigen

Any foreign substance that enters the body and triggers an immune response.

Antibodies

Specialized defense proteins synthesized by the immune system in response to an antigen.

Enzymes

Catalytic proteins made of strings of 100 to 1,000 amino acids with unique shapes that accelerate chemical reactions in the body.

Hormones

Chemical regulatory messengers formed from lipids or proteins (such as insulin and glucagon) that coordinate body functions across organs.

Limiting amino acid

The specific essential amino acid supplied in the lowest amount relative to the body's requirements for protein synthesis.

Deamination

The removal of the amino group from an amino acid occurring primarily in the liver, yielding a keto-acid for energy and ammonia that is converted to urea and excreted in urine.

Nitrogen balance

The relationship between the total amount of nitrogen consumed in the diet versus the amount excreted by the body.

Positive nitrogen balance

A physiological state in which nitrogen intake exceeds nitrogen excretion, occurring during growth, pregnancy, and recovery from illness.

Negative nitrogen balance

A physiological state in which nitrogen excretion exceeds nitrogen intake, occurring during starvation, low-calorie dieting, AIDS, and cancer.

Complete proteins

High-quality proteins that furnish all essential amino acids in amounts necessary for human health, such as animal proteins and soy.

PDCAAS (Protein Digestibility-Corrected Amino Acid Score)

A standard measurement evaluating protein quality based on its essential amino acid content and digestive availability, scored on a scale from 0 to 100.

Incomplete proteins

Dietary proteins that lack adequate amounts of one or more essential amino acids, including most plant sources like legumes, grains, and vegetables.

Complementary proteins

Two or more incomplete protein foods that, when consumed together, provide adequate amounts of all essential amino acids.

Recommended Dietary Allowance (RDA) for protein

The daily intake target for healthy adults, established as $0.8\,\text{g}$ of high-quality protein per kilogram of body weight.

Acceptable Macronutrient Distribution Range (AMDR) for protein

The percentage of daily energy that should come from dietary protein, established as $10\%$ to $35\%$.

Vegan

A vegetarian dietary pattern that eliminates all animal flesh, seafood, and animal products, including dairy and eggs.

Lacto-vegetarian

A vegetarian dietary pattern that includes dairy products while excluding meat, fish, poultry, and eggs.

Lacto-ovo-vegetarian

A vegetarian dietary pattern that incorporates both dairy products and eggs while omitting all meat, poultry, and fish.

Macrobiotic vegetarian

A dietary pattern focused primarily on whole grains (notably brown rice), vegetables, soy, legumes, and fruits, sometimes including whitefish, while avoiding meat, poultry, eggs, and dairy.

Semivegetarian (flexitarian)

An individual who mostly consumes a plant-based vegetarian diet but occasionally eats meat and seafood.

Protein energy malnutrition (PEM)

A severe nutritional deficiency syndrome caused by inadequate intake of protein and/or total calories, recognized by WHO as the most lethal form of malnutrition.

Marasmus

A severe form of protein-energy malnutrition caused by starvation and insufficient intake of both protein and total calories, characterized by extreme emaciation and a skeletal appearance.

Kwashiorkor

A form of malnutrition caused by low protein intake and altered gut bacteria, characterized by a swollen abdomen and edema, frequently occurring when young children are weaned from breast milk to cereal.